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FAQs on Pond Repair: Leaks/Leaking

Related Articles: Pond Repair Work, Liners for Ponds,

Related FAQs: Water Feature Repairs 1, Water Feature Repairs 2, Water Feature Repairs 3, More specifically: Seepage, Earthen Pond Repairs, Waterfall Repairs, Electrical Problems, Fountain Repairs, Faux Rock Repairs, Crack Repairs... & Foundation Coatings, Liner Pond Repairs, Liners in Pond Construction,

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by Robert (Bob) Fenner

Pond repair question        5/21/15
Hi Bob,
I recently bought a property in northern Vermont, neglected for many years, with a large (1/2 acre or about 20,000 sf) bitumen asphalt pond.
<Oooh, olde school>
The pond should be around 7' deep but has a leak at roughly 4'6". There is a drain valve in a manhole which I tested and works fine. My plan was to drain the pond, either fully and muck it out,
or enough to expose the leak cracks and then fill and seal them.
I am reluctant to fully drain it at the moment as there are many frogs and salamanders breeding - and I think one snapping turtle which I'd like to get rid of.
<Yes; I would>
There are many cracks around the sloped edge with organic material growing out of them. Fortunately, a metal snow shovel seems to clear off most of it.
<I'd consider making a shotcrete (and color) berm... with anchored pencil rod re-bar and mesh (chicken wire likely)>
What would you recommend patching it with?
<Maybe more asphalt emulsion... Henry's or such... But... really... best to have the soil tested... IF you want a more permanent improvement... See WWM re liners...>
My thought was to gouge out the cracks and fill with either hydro-cement or asphalt/bitumen.
<Worth trying>
Is there a plastic or polymer solution to this?
<Not as far as I know; no>
During Feb/Mar, I measured the surface ice to be 16"+, so freeze/thaw is another problem.
<Yes... a few approaches to this as well... the slope and berm...>
See pics attached...
Many thanks,
Wendell Anderson
<Let's keep chatting till you're aware of your choices here. Bob Fenner>


Re: Pond repair question        5/21/15
Hi Bob,
Thank you. See below.
<Uhhh; a mess for others to read through>
> Subject: Pond repair question
> Hi Bob,
> <Wendell>
> I recently bought a property in northern Vermont, neglected for many years,
> with a large (1/2 acre or about 20,000 sf) bitumen asphalt pond.
> <Oooh, olde school>
> The pond should be around 7' deep but has a leak at roughly 4'6". There is
> a drain valve in a manhole which I tested and works fine. My plan was to
> drain the pond, either fully and muck it out,
> <How?> {was thinking to drain it fully and rake/shovel it out)
<<DO look into buying or renting a trash-pump... diaphragm type if there's much in the way of larger solids... And I suspect there will be further damage from entering the pond>>
> or enough to expose the leak cracks and then fill and seal them.
> <With...?>(Thoroseal WaterPlug in cracks, cover in Thoroseal or bitumen driveway sealer, Henry's roof sealer?)
<<NEED to know if the damaged area is expansive... i.e. if it's moving at all. If so the Thoro products won't work; nor asphaltous material if much wet, flexible.... might try a patch... of roofing material AND the Henry's... will require a few dry days to dry the pond, dry the repair>>
> I am reluctant to fully drain it at the moment as there are many frogs and
> salamanders breeding - and I think one snapping turtle which I'd like to
> get rid of.
> <Yes; I would>
> There are many cracks around the sloped edge with organic material growing
> out of them. Fortunately, a metal snow shovel seems to clear off most of  it.
> <I'd consider making a shotcrete (and color) berm... with anchored pencil
> rod re-bar and mesh (chicken wire likely)>(I think this will be Plan B - assume you mean just the top edge to below present waterline where leak is, will it adhere to the underwater area after draining enough to expose and dry it) (I walked it and there is roughly 500' of perimeter x 6'-8' of exposed berm, about 30" in elevation depth)
<<Yes to over the existing edge throughout>>
> What would you recommend patching it with?
> <Maybe more asphalt emulsion... Henry's or such... But... really... best to
> have the soil tested... IF you want a more permanent improvement... See WWM
> re liners...>(I assume a 1/2 acre liner would be most costly? - Plan C perhaps)
<<I'd count on a half dollar to a dollar a square foot... for the whole project... IF the soil can be mixed w/ an impervious clay... might hold, be cheap>>
> My thought was to gouge out the cracks and fill with either hydro-cement or
> asphalt/bitumen.
> <Worth trying>(Plan A, as above with ThoroSeal plug)
> Is there a plastic or polymer solution to this?
> <Not as far as I know; no>
> During Feb/Mar, I measured the surface ice to be 16"+, so freeze/thaw is
> another problem.
> <Yes... a few approaches to this as well... the slope and berm...>
> See pics attached...
> Many thanks,
> Wendell Anderson
> <Let's keep chatting till you're aware of your choices here. Bob Fenner>(Thanks again...)
<<Cheers, BobF>>

Spring fed water feature       4/4/15
Hello, I've been looking everywhere online and your web sight seems to have the most diverse information and consequent knowledgeable replies that my help me with my unique situation. The following is a description of my water feature.
<Let's have it!>
I live in a hilly wooded area with natural springs popping out in every ravine. The original homeowner dammed the ravine nearest and about 30 feet higher in elevation than the house and ran a 1.5" pipe from the pond behind the dam to a waterfall and small brook he built on the back of the house.
The waterfall is 5' tall and 4' wide. It fills a small 2 foot wide "L" shaped pond 1' deep, the short leg of the "L" is in front of the waterfall and the long leg is 8'. The flow out of the "L" shaped pond overflows to a 2' wide shallow brook that continues 30' flowing gently down hill back into the ravine. These features were all constructed with natural stone laid in concrete.
<No liner underneath....>

The waterfall and the brook sides are built with rounded stones and the pond and brook floors were built with flagstone. This was all built in the 1970's. The last 2 years I've experienced severe frost heave on posts supporting an outdoor bar I built 15 years ago that is beside the water feature.

With it being spring feed, running continuously year round a leak is not obvious and being in place for over 40 years there is a tremendous amount of calcified growth, especially on the waterfall. I'm planning to install a French drain between the bar and the water feature to control the spring leakage. Ideally I'd like to install a liner but that's not practical. So I've diverted the spring flow away from the waterfall and brook and I'm jack-hammering off the calcified waterfall growth to get back to the original stone. After that I'll start looking for leaks.
<Mmm; not likely productive>
With all the above background information what will be the best method to seal the leaks and realizing that I'll never be leak free do you think the French drain concept will interrupt the sub-surface water movement to eliminate the bar structure post supports from frost heaving.
Jeff Dieterle
Northern Indiana
<Thank you for writing; and your kind initial words. The leakage can really only be addressed in a permanent way by applying the liner.... As you'll see it is VERY hard to locate leaks about rock/concrete... and even small joints twixt them can result in huge seepage of water. I do think your diversion of water and removal of calcification is worthwhile... but almost assuredly you'll have to lay in a liner anew a replacement feature (rather than using the existing), as the current is not likely to lend itself to modification. Bob Fenner> 
Re: Spring fed water feature
Thanks for the quick reply. There is no liner behind the waterfall or under
the brook and I realize that a liner the only way to stop leakage.
<Yes; the only assured way>
I'm not
sure how I would rebuild the waterfall with the liner behind it and replicate the original design.
<Won't be original... if possible, practical, building over the existing, using it as part of the structural trough is the route to go... extending the liner as the stream>
I'm still jack-hammering the overgrowth but
it appears that a single vertical row of rounded stone was laid with
(instead of mortar) and tight against the block wall behind the waterfall.
<Very typical in time failing. Bob Fenner>

Small Koi pond; leaking, reading      2/16/15
Not sure if this is the right spot but we recently converted a old planter into a fountain. It's made of brick and concrete and there are some small leaks. Looks like the water is seeping through the concrete seems.
The inside has elastomeric waterproof undersealent. We don't know what to use to fill the cracks to stop leak.
<There are a few options to try... Read here:
and the linked files above. Bob Fenner>

Leaking Pond /Darrel (!)
Dear Bob,
A year ago I corresponded with you (and appreciated your helpful answers!)
about building a pond. I followed your advise and hired somebody to do the mixing of concrete. He used a bit of concrete on the walls over chicken wire, but then covered the bottom and walls of the pond with Multiset modified thin-set mortar for floor and wall tiles (by Custom Building Products company).
The pond is slowly leaking and I believe that water permeates the mortar as it is probably not designed for continuous exposure to water and under pressure to boot. I can see a wet strip of mortar above the water line where the water presumably seeps in by capillary action. Is there anything I could do to make the surfaced waterproof? Preferably cover/paint it with something rather than using unit for which I would need special equipment.
I would prefer to do it myself as I do not trust the guy who did it anymore. (In addition to the leakage, there are other reasons for not dealing with him anymore.)
Many thanks for your advise...I certainly hope you can come up with some do-able solution. Best wishes, Zuzana
<Hi Zuzana>
<I'm not Bob so I left your email specifically for him -- but I HAVE had a leaky pond, so I thought I'd jump in {pun intended!}>
<I've built a number of ponds over the years and I've encountered many others in various forms of disrepair and I'm vary familiar with concrete-over-chicken-wire construction and the leaks that come along with that.>
<After you drain the pond you have to do a close inspection of the entire pond for structural problems. What I'm saying is that no coating that you're going to apply without special equipment is going to fill large gaps or fill any gaps that flex or expand. If you have any structural problems or cracks they have to be fixed the old-fashioned way, which is to say grinding them out and using a good quality cement (like Quick-Crete sold at building supply stores) to get a proper structure.>
<In connection with that you have to prepare the surface for whatever coating you're planning to use. This usually involves a scrub with diluted muriatic acid to clean and etch the surface. No special equipment, but it's messy and stinky and you need to rig up some ventilation because you don't want to breath the fumes.>
<Just link in painting ... preparation is everything. The more time you spend in preparation the more time you'll spend ENJOYING your pond rather than draining and repairing it. What I mean is... when you think you have the surface prepped perfectly... work on it some more.>
<Now this brings us to the faith-based portion of the job. I have heard for years about a wonderful product called Thoroseal and I've heard many a professional pond builder rave about it. It's never worked very well for me. I've used a gray Thoroseal paint to seal a concrete waterfall and it seemed to work fine and lasted about 5 years.>
<What I used - and I'm only giving you my opinion {worth every penny you're paying for it} is Nelsonite PoolPoxy. If you use PoolPoxy2 you'll have a durable finish that will last 10 years. If you use PoolPoxy Hi-build over Nelsonite Primer the people who buy the house after the people you sell it to will probably have to pay someone to break it up & haul it away>
<If you go this way - or even go the Thoroseal way - follow the manufacturer's instructions to the letter & in the slightest question contact them for clarification. I'm sure Bob will agree that when it comes to most complaints about coatings, most include "well, I skipped that step and I short cut on this other step...">
<Best of luck - Darrel>
Leaking pond /RMF

Dear Bob,
A year ago I corresponded with you (and appreciated your helpful answers!) about building a pond. I followed your advise and hired somebody to do the mixing of concrete. He used a bit of concrete on the walls over chicken wire, but then covered the bottom and walls of the pond with Multiset modified thin-set mortar for floor and wall tiles (by Custom Building Products company).
<Sounds good thus far; but; where's the liner here?>
The pond is slowly leaking and I believe that water permeates the mortar as it is probably not designed for continuous exposure to water and under pressure to boot. I can see a wet strip of mortar above the water line where the water presumably seeps in by capillary action. Is there anything I could do to make the surfaced waterproof?
<Yes; will necessitate emptying, cleaning, likely acid/bleach washing and drying the basin first>
Preferably cover/paint it with something rather than using unit for which I would need special equipment. I would prefer to do it myself as I do not trust the guy who did it anymore. (In addition to the leakage, there are other reasons for not dealing with him anymore.)
Many thanks for your advise...I certainly hope you can come up with some do-able solution. Best wishes, Zuzana
<Please read here:
scroll down to Water Feature Repairs. Bob Fenner>

Waterfall. Help! Common construction error leak    2/23/13
Dear Bob,
We have a beautiful unfinished waterfall that leaks the rocks at the bottom of the falls are so large that we didn't put a liner underneath.
<Should have put over then... all the way into the basin...>
We used a pool stop leak mortar
<Won't work>
 to seal the rocks and the upper liner to the main fall rock. We are in New England and the mortar cracked in no time. Now we have a quote from some contractors to help us finish the falls and they recommend moving the big two fall rocks with a tractor which could take a whole day they are so large. Also it was very hard to position them even with heavy machinery the first time. On the end we would still have three liners. One for the upper falls, one for the lower and one for the pond.
<These need to overlap, be solvented (above water)... together...>
This seems like a very difficult and expensive proposition especially considering I am great with masonry and we don't have the money to do this.
Help! Is there a mortar we could use that would at least last several years?
<None... the "moving" of rock, mortar will cause the latter to crack>
We have seen other mortared waterfalls I the area but not sure how they were built. Thank you!
Liz Coello in Connecticut
<Do read here (again?):
and the linked FAQs files above... I would lay a liner on top of the "waterfall trough" and put wire mesh, mortar over this... with the discharge pipe of the fall dumping water into the liner/trough, and the liner extending (drain the pond down a foot or so to do this) into the basin/pond. Understanzee? Bob Fenner>

Rock Pond Repair  8/1/12
Sir/ Madam
I have a 5 meter long,  1 meter  wide , odd shaped rock pond. It had been empty for many years but I would like to repair it and get it up and running again. It is made of many large volcanic rocks which are joined with concrete and has a concrete floor, which had been calked over some years ago.
<An apt description of what I see in your pic>
Recently  I filled it with water and saw there was a slow leak,
<Yes; very common w/ these sorts of rock ponds, or any rock that penetrates the edge/wall>
 I would think caused by small cracks from an earthquake or plant root damage.
<Yes; there's always settling... even if the rock is set on, originates on the original grade>

I have called a professional  and they offered me a quote of 7,500 USD to repair and set up lights, filters  etc. As I plan on keeping just a few goldfish and listening to the small waterfall then this price is out of the question. My enquiry is , what do you think is the best way to repair it cheaply...can I cover the rock, cement, old calking with a rubber paint.
<... a few approaches to consider... An elastomeric paint of reasonable color the cheapest route to go... need to clean the surface, or resurface... w/ a good mortar... and follow directions for application explicitly... All the way to the most sure repair, installing a liner...
These are covered by reading here:
scroll down to the Repairs tray and read>
I tried taking out the calking but this also was difficult. 
Could I  fibreglass over the old rock,  concrete and calking .
<You could... a mess, and not really a long-term repair. Will fail w/in years>
 I would really like to have the pond and small waterfall running but have a budget of only a few hundred dollars .
<Then not glass and resin>
( Any cheap option is ok, even if I had to do the repair  again after a few years )
A professional here in Japan is just simply out of my financial range.
Hope you can help...Regards
Jonathan Garvey, Kyoto Japan
<Read and write back for clarification. Bob Fenner>

Re: THANKS, pond repair in Japan    8/2/12
Dear Bob Fenner,
Thank you so much for taking the time to  respond to my enquiry.
Unfortunately, here in Japan there is not much information and even fewer supplies for ponds...Nobody has a garden let alone a pond!
<In places... not "in large towns". I grew up there in Kyushu>
So I am very grateful for your suggestions.
I shall try to have it re-mortared, and to get some elastomeric paint...also not available here but I think somebody might ship from the US.
<Maybe; worth asking>
Once again Thanks ...and I shall let you know how it goes along
<Thank you>
PS the liner is not really a suitable option as ; the pond is odd shaped, has a bridge over it , and an overflow pipe right in the middle under the bridge
<The liners are flexible and cut-able in place... but I do understand.
Cheers, BobF>

Leak in concrete fish pond  6/26/12
My concrete Koi pond is 50 years old. It is brick on the outside and concrete on the inside. It is about 1/2 in the ground and 1/2 above ground level. The inside dimensions are 12 ft. From side to side, 5 ft, from front to back, 26 in. deep and is built with back a part of a brick wall.  There is a hole drilled through the pond and brick wall, through which the hose pumps the water into a UV filter.  The filter then sends water through another hose which directs the water through a lion's head on the wall and spills back into the pond.
The hose that goes from the pump through the wall and to the filter is 3/4 inches and I need more water flow.
<Best to drill/rotohammer this out now... ahead of the leak repair... such tools, bits of size can be rented from various places>
The hole is, also, in the corner of the pond and touches the side of the pool. It is almost impossible to seal the hose on that side of the hose.
<Best to abandon, replace at this point/juncture>
I would like to fill that hole
<See WWM re "Water Plug" by Thoro Products>
 and make another hole further from the wall and use 1 1/4 in. pipe to which I would attach 1 1/4 in. hose.  The hose through the wall has flexibility which I think might create leaks and the 1 1/4 pipe would be rigid.
Will I be able the fill the present hole? And, if so, what product would I use?
<Please read here: http://www.wetwebmedia.com/PondSubWebIndex/LeakRepF.htm
and the linked files above. Bob Fenner>

pond leakage   3/11/12
Hello crew @ wet web media,
<Hiya - Darrel here>
I have a recurring problem in my Koi pond and maybe you can give me the best route to fix this. I live in the northeast and have a Koi pond that the previous owner had constructed out of cement, due to the freezing issues in my area I have developed cracks in the pond that seem to be leaking water
<I feel your pain>
I would like to make a permanent fix and am thinking of putting in a pond liner.
<Sometimes I consider a more permanent fix would be filling it in with dirt and building a storage shed over mine>
My question to you is - can I put a liner in over a concrete pond?
Will the liner hold the water back from leaking between the liner and the cement?
How do you attach the liner to the cement?
<Well, Gravity attaches the pond liner. In other words the weight of the water will keep the liner down. You have two challenges, both easily addressed.>
<The first is the shape of the liner. As you lay the liner into the empty pond, you'll find that the EPDM pond liner will conform to every shape under the sun … except your shape. You will at first find folds, creases and flaps that are maddening. With the right amount of tugging, folding and complaining, you will eventually wrestle the liner into decent position and they sell a special double faced tape for seaming that also can be used to hold a flap down tight against the bottom. It's really hard to explain, Karl. It's not a HARD job … meaning it's not complicated, but it's challenging. The best I can say is AFTER you've done it you'll think "OK, that wasn't so hard after all" but DURING the project, you'll be tempted to think many unkind thoughts.>
<The second challenge is the edges. In NEW pond construction, you just lay the extra liner up the sides and over the edges and then build an edge guard over the liner (like a ring of rocks, etc.) and then just cut away the excess liner. Since your pond already has an edge, my first suggestion is that you dig a trench around the edge of the concrete so that you can fold the liner OVER the concrete edge, down into the soil and then bury it. If your pond already has an edge trim and you need to run the liner up to the edge and just cut it an inch or so about the water line, THEN you'll need some EPDM adhesive to glue the edge of the liner to the properly prepared and sanded concrete edge.>
Any answers you give me will be greatly appreciated
<Well, Karl. Those are the answers. I may have made it sound ominous, but in the overall scheme of things it's really not.> 

leaking pond 10/6/11
We just had a 30 foot long waterfall/fountain installed that has an 8x7x2 foot retention pond. The pond will not hold water. The recirculation pipe in the bottom does not seem to be the source of the leak.
<Mmm, have you plugged and pressure tested the related plumbing yet? This is the first area to investigate. Your installer or any licensed plumber will know how to, have the tools to do this>
It appears as if there are various very fine holes in this poured concrete pond wall areas. The contractor has hydraulic cemented the area and used the product Thoroseal, applying two layers.
<I am a big fan of this and most other Thoro products>
Water appears to still be leaching in from these various fine holes as the Thoroseal on these areas does not dry.
<? Was this surface cured thoroughly before the basin/s were filled? DO read on Thoro's site re application: http://www.thoroproducts.com/products_waterproofing.htm>
What would you recommend as the next step to create a leak free pond?
Thank you!
Carol Galant
<Mmm... there are a few approaches. Best to have you read here:
and the linked files above... while you're having the plumbing tested. IF the concrete and ThoroSeal have been applied properly, they are not likely the source of leaking.... other "through-put" items... like the plumbing, rock work... more likely. Bob Fenner>
Re: leaking pond 10/6.5/11

Thank you for responding so quickly. The first thing my installer did was to check the plumbing and pressure test the lines.
Both of these did not have a problem.
Yesterday, the installer again used hydraulic cement on the seeping holes, about 7 of them, added "Fix-A-Leak" and ran the pump all night.
The level has dropped about 2 inches over 20 hours.
<Too much...>
There is no "rock work" that water can leak through. The pond is completely cemented.
Decorative rock has been cemented to the top edges but the water line is 5 inches below that edge.
<Understood... it's the basin itself that is leaking... Oh, how I wish, and I bet you too, that the install had a waterproof membrane>
I am thinking a rubber liner of some sort is the next step.
<Mmm, yes...>
But, with the rock already being cemented to the edge, I am wondering if the use of the EPDM liquid rubber paint on liner would be the next step.
<Maybe; though I dearly wish I had all the money thrown away on these applications that did no good. If it were me/mine, I'd try another coat of Thoroseal ahead of treating the existing work as a hole in the ground (installing a liner) OR another sealant>
Thanks again!
Carol Galant
<Welcome. BobF>

Leaking Mountain stone Koi pond 11/13/10
We have a Koi pond built in 1929 that is constructed of mountain stone with cement mortar . It has 3 upright planters constructed of Mountain stone to protect the plants. We are having a leaking problem due to damage from a storm that dropped a tree limb into it that appears to have dislodged some of the stone work. We can see no cracks but the water level is going down.
We have been advised that we must remove all the stone work and replace it with a liner.
<This is... the most-assured repair. Patching, applying "sealants" are very doubtful to effect a lasting repair>
I hate to do this as the pond is really quite lovely to look at. It is 12 feet in diameter and about 1 1/2 ft deep. Do you have any suggestions?
<To take care when taking apart; take your time... perhaps some photos, labels to assist in reassembling>
Any help you might give would be greatly appreciated. I just found you site and it is wonderful. Thanks so much for taking the time to read this.
<Mmm, you likely have read here:
and the linked files above. Bob Fenner>

Re: 50 year old concrete goldfish and Koi pond - 8 months later 8/15/11
Good morning, Bob. Long time no talky to. I hope all is well with you.
<Yes. Thank you Shirley>
So, here I am a year later from when I first began my pond re-do journey. To update, in a nutshell - all is excellent! I used Thoroseal on the new concrete (inside the pond). That was a chore because the outdoor temperature needed to be 60º for optimum results, and it was a rainy and chilly November in Oregon. So I built an insulated "tent" over the pond and installed a heater and fan inside. I did all the work inside this cave, over a two week span, in the middle of winter. I was ever so mindful of following the Thoroseal directions to the proverbial T. I even messaged with the TS people to be sure I was doing the best I could under the wintery circumstances. The end of the TS story - I love Thoroseal! I have read other posters' comments about TS (some not so complimentary) but it worked perfect for me - but it is soooo important to NOT be in a hurry, and to follow the directions explicitly with no fudging on any steps.
<Ah yes>
So now, jump forward. Pond is full. 55-gallon bio filter and 55-gallon settling chamber is installed and working perfectly. My semi-gravity bottom drain works marvelously. I'm using a 1200 gph Mag-drive pump submersed in the settling chamber, which draws water through from the bottom drain in the pond; this water is pumped into the bottom of the bio filter, and then overflows back into the 1100 gallon pond. My home-made skimmer is a life-saver. I bought my first new Koi last weekend after waiting all summer for the sunlight to propagate the good bacteria/algae so that the pond would finally clear (with no chemicals or UV light). I am now ready to "finish" the rather unsightly top and outside portion of the pond (see attached photo).
<Vey nice covers>
I will be using either slate or quartzite 12" x 12" x 1/2" tiles for the (horizontal) top - each tile to be custom cut into mitered wedges to fit the contours of the irregularly shaped pond. Sounds daunting but I did a trial run with paper and it's easier than I anticipated to create the templates for each tile (I'll need a tile saw, of course). After the tiles are mortared into place, I will be adhering 4"-6" travertine chair rail pieces around the outside top perimeter along the edge of the tile, and then grouting all. And then I plan to use a color-tinted stucco for the outside vertical wall. A lot of work, but do-able, and I think it will be lovely. So, why email you, you ask....
What should I use for the mortar to affix the slate tile to the top, and the grout (1/4" grout lines)? Rain, of course, will be running off of this capstone and into the pond. It was suggested I use a multi-purpose mortar/grout - and if I did, could I use an acrylic additive as the wetting agent to make the mortar more stable/harder/better adhering/safer for fish?
<Yes to these>
Can I use plastic cement (if I can find it) for mortar and grout? What would you suggest?
<I would use the multi-purpose... mixed w/ a blending bar, attached to a variable speed drill... in batches... with the additive>
Oh, and then there is the final landscaping.
I love my 50 year old concrete pond! I love my bio filter and settling chamber design. It is practically maintenance free, and the fish are thriving.
Thank you for all your previous help. I hope you have had a marvelous summer!
Shirley in Oregon.
<Thank you; BobF about done in Maine>
ps. The image you uploaded onto your web page, that I sent you of my filter design, is kind of hard to make out - somehow there are two images there, one on top of the other, making it hard to tell what is what. Just thought I would mention it in case somebody wanted to consider a similar design for their project.

Leaking concrete pond 9/30/09
I just found your website and have a question. We have a very large pond that originally was a swimming pool - concrete and rebar. It has numerous cracks now and only holds water to a low level. We're right on the water table - living on a bayou in Florida. A pool place suggested rather than empty it and reconcrete, etc at great expense, we should create algae which should seal the cracks. He advised us to add nitrogen and phosphate and fill the pond in order to grow algae and thereby plug up the leaks.
<Mmm, no... Too likely to have ongoing REAL problems with excess algae... insect vectors even as a consequence of so much algal proliferation>
Is this a good solution to the problem?
<Not IMO/E>
Will these chemicals harm my water lilies, fish and other plants?
<Can, yes>
It sounds good to me but I'm hesitant without some feedback. Any info you can provide will be GREATLY appreciated. Thanks in advance. Kathy Gresko in Florida.
<The least expensive, most sure repair/solution is to place an adequate liner over the existing structure/basin. Please read here re:
and here:
and the linked files above. Bob Fenner>

Repairing & refilling Koi pond 8/20/09
Hello Crew!
I desperately need some help, suggestions & answers re: repairing & re-installing a Koi pond. After a frustrating search for the source of the leak(s), we have faced the conclusion that the pond will need to be re-lined rather than repaired. Here are the basic facts:
. in-ground, rubber liner, about 1600 - 1800 gal, about 7 y/o.
. using an exterior biofilter from Tetra which has never been back flushed; pump to biofilter more than adequate for turnover of water, about 2000gph
. water quality is clear, algae-free, water chemistry is good (ph, nitrate, 02 etc.)
. currently stocked w/5 Koi (9" - 16") + 3 baby Koi <4", + 1 comet (6").
All are healthy, vigorous, beautiful!
. planted w/Anacharis, water lettuce, water hyacinth.
This pond is also contiguous to a "bog" area, rubber-lined & separated from main pond by rocks, planted w/thriving iris, pickerel weed, arrowhead etc.
The main pond has been losing about 6" water daily & have been re-filling w/garden hose every 48hrs or so.
Currently in the NYC area, the weather is very hot, 90+ w/no real end in sight to the heat wave. It's also been raining often & heavily, so between the heat & the rain, it's been hard to be able to get at the pond. We've tried unsuccessfully to identify the leaks, so are now planning to dismantle the pond, re-line & return the fish, plants etc.
The dog work of removal of rocks, plants etc. will be daunting, but we are willing to do this ourselves. The tricky questions are about how to "warehouse" the fish & how to re-store quality to the pond water.
<Big "wading pool">
Due to budgetary concerns, we are definitely going to have to improvise how to hold the fish & do all the work ourselves.
1. How to store the fish safely? In 55gal plastic garbage barrels?
Small (450g) wading pool?
<Much better>
Water would come from pond, itself.
2. What kind of aeration system will we need to keep oxygen levels in water? What kinds of pumps, airstones etc.?
<Best to use what you have currently...>
3. How to keep water temp low enough? Shade w/patio umbrella? Floating plants? Bags of ice?
<All the above>
4. How long could the fish survive in this environment?
<Easily a week or two>
5. What are the best ways to re-store pond water quality?
<Return the stored water and filter sans cleaning>
How long would it take before it's safe to return fish to their pond?
<... immediately. Add some water conditioner for the remaining 1k or so gallons you're adding new>>
There'll be some microbial benefit from returning water that the fish have been kept in, also from plants, running the biofilter & pumps. What about adding commercially available de-chlorinators, microbe-lift chemicals? Suggestions for brand names?
<Kordon/Novaqua or API equivalent... Microbe-Lift's products are very good>
6. Am I crazy to even think about trying this myself?
<Not crazy at all. Just need some strong help to lay down/over the new liner (Oh, and do take care when stepping inside the current one... treacherously slippery>
The pond, the fish, the plants, the water have been a labor of love & a are great source of pleasure. The pond was made by myself & another friend, ourselves. We made all the classic beginning mistakes, but the pond has been thriving & flourishing. I bought the fish when they were small at a local aquarium shop & they have grown into beautiful beautiful creatures.
I would hate to lose any of them.
<Should do fine... just take your time>
After an internet search, I was very happy to have found your site, it's the most helpful & knowledgeable of any I've read. I hope to hear from you soon.
Thank you for your time & consideration.
-- Mark Harada --
<Glad to help. Bob Fenner>
Re: repairing & refilling Koi pond 8/20/09

Wow, thank you so much for answering so quickly & in such detail!
Feeling much better about the whole thing, now. My main fear was that we'd end up poaching the fish!
<Not to worry>
The only thing I'm not clear about is your suggestion to use the same pump that we use for the pond for the kids' wading pool. Won't it be too strong for a much smaller volume of water?
Thanks, again,
-- Mark --
<Will not be too strong, I assure you. BobF>

Koi pond, leak... 1/10/09 Hi, <Dawn> Your site has been of great help during the construction of our first pond. I have run into a problem that is not really addressed any where so your help would be wonderful.. We have built a Koi pond for a client in the Virgin Islands. It is about 900 gallons and is concrete, the seal is Thoroseal with a grey green dye. The pond has an Island in the middle on which sits a large rock 3'x4'x2'. A pipe is run through the rock <Mmm, no liner I take it... and this pipe somehow has water about it... either from the fall or penetrating the basin?> to the top and then through a copper bowl. A slow fountain pump fills the bowl with water which then spills over the rim of the bowl and down the sides of the rock. It was decided to raise the water level about two inches above the joint between the rock and the concrete pond. <Ohhh, likely leaking> We have begun experiencing a leak which stops as that joint is reached. Since the leak is about 1/2" in a 24 hour period and since the owner would really like the water level to stay the two inches up the rock we are wondering about sealing the rock in two areas. <Mmmm> 1.) To solve any leaking at the joint which we suspect is the major problem (due to normal expansion and contraction of the rock:) put a two inch silicone bead at the joint (however I see on your site that silicone may not seal a joint between rock and concrete) or put a two inch collar of epoxy grout which should seal to both the rock and cement with no problems. Finally the last choice would be to build a cement and ThoroSealed collar over the joint extending just above the desired water level <Mmm, none of these is likely to be effective... Thoro has other products> And if we fix the first problem but still have water loss then we would proceed to fix #2. 2.) To solve the problem of both excessive evaporation from the fountain water hitting the rock and to solve the porosity of the rock from soaking up water from the fountain we thought that sealing the rock with a water based stone tile sealer like Aqua Mix Sealer's Choice Gold might work. <Not likely at all unfortunately> It is clear and there is no shine and it is good for exterior use. Of course we would first try it on a small area of the rock before leaping into this fix. If you have any suggestions about either of the two problems or the products that we have come up with I would be most grateful for your help. Thanks, Dawn <Your "for sure" options are few... rebuilding all over a water-proof liner. Please read here: http://wetwebmedia.com/PondSubWebIndex/thorselfaqs.htm Bob Fenner>

Re Leaky Koi Pond 01/13/09 This is a follow-up to mashngo's e-mail about my pond. We could not use a liner as we started with an 8ft x 4ft x 4ft bluebit granite rock at the pond's center. <Been t/here> We dug a doughnut around it to 4 ft and lined the perimeter with reinforced block/cement over painted with Thorough Seal. <As I understood, understand> We appear to have a slow leak at or around the rock/block border. <Very common> See my drawing. <Very nice illustration> Any ideas for sealing the rock itself or the interface would be very much appreciated. <Mmm, the "next level" approach I might take here (other than abandoning the current structure, emplacing a liner over all... adhering this to the border/rock, above water level) is to use another fine Thoro product called "Water Plug"... needs to be mixed up, used in small patches (cures quickly)... practice, measuring for added color (if being used)... to match all the way around... the area needs to be thoroughly clean... no biological film present> I don't want to change the "look" of the rock with the sealer. Does Thorough Seal absorb water? <Mmm, minimally> Thanks, Jack <Welcome Jack... I do hope I'm being a bit more clear, complete here. Do contact me if not. Bob Fenner>
Re: Leaky Koi Pond Hi! Bob, <Jack> And thanks for the prompt reply. Your message is very clear but I don't think we have the space to line the existing structure and hide the rock / liner interface with rocks or a ledge etc. So for now at least we'll try to plug the leak. <The Water Plug product is a worthy try> But thanks. I did not mention that there is a waterfall spilling down the rock and there may be some water loss into the rock by absorption or via fissures. Is there a clear spray or brushable sealer out there that will not significantly change the look of the rock but seal it? <There is not... or to be more fair... All of the ones I have had first, and reliable second/other hand experience with have not proven efficacious... I might try dabbing the Water Plug in the crevices twixt the rocks in the fall> Fish/plant safe of course. The reason that we are all so paranoid about water out here is that the only water available infrequently falls out of the sky. Or you can buy it for about $1 per gallon. <These materials have neither "body" nor "stretchability"... and surprising to many folks... rocks do "move"... expand/contract with temp., moisture/drying...> Thanks again. Jack. <Welcome. BobF>

Re: Leaky Koi Pond, fixed, now high Alk. from Thoroseal 2/13/09
Thank you for your help earlier. I now have a leak-proof pond. The ThoroSeal finish was really helpful. <Thoro does have some very useful products for sure> I am now having problems controlling the pH which, uncontrolled, will drift up to >8.5 in 48 hours. <No worries... allow to "soak" for a few days, drain, perhaps do a dilute acid-wash (see WWM re), and re-fill> The whole pond is ThoroSealed and I use only rain water for filling. The rainwater's pH is 7.5. I have nothing else in the pond likely to affect pH I noted that on the MSDS for ThoroSeal it says that it is alkaline, but does not say how much. <Yes... tis the alkalinity in this product that has bolstered the pH here> Does the alkalinity leech out and finally go away. <Yes> Is there anything else I can do other than keep adding acid? <Mmm, time going by...> Thanks. Jack <Please read here: http://www.wetwebmedia.com/PondSubWebIndex/acidblchpds.htm and the linked FAQs files above. Bob Fenner>

"Water Loss", pond 6/10/08 Hello, I got a question in regards to my 12' X 14' X 4' (deep) Koi pond with a 4' in length of stream (about 16" wide).&I live in Southern California, and is it unusual to lose about an inch of water over 24 hours period given my set up/weather here? <Mmm, such amounts can be due to "simple" evaporation... given low humidity, high/er temperature, wind...> Please let me know. I've looked around the pond trying to detect any possible leak and I've yet to see any evidence of that. <There are companies who specialize in detecting such leaks... If this amount of water loss is prohibitive (we live in San Diego... so know the cost of water) or a concern in terms of not knowing where it's getting off to... perhaps damaging someone's property... I would look in the Yellow Pages (see Swimming Pools... repairs), and call a co. re. Bob Fenner>

Leaking pond - help! 8/19/07 Hello, <Good morrow to you> Great posts under "Leaking pond - help!". I'm thinking the answer to my pond problem is somewhere to be found... <Perhaps> We have a small (>200 gal) backyard pond (-24" deep) with recirculating water fall. No fish... just for sound and looks. <Okay> The front pond wall is stucco over concrete block. The stucco-ed wall had cracks and loose stucco has been removed. The pond has a back wall of flat masonry stone. When filled... about 2/3 of the stone wall is under water and fortunately the stone wall side of the pond does not leak. (See photos) <I see these...> I have read that a flexible liner is best for ponds but I do not want to cover the stone portion. <Mmmm> Is there any way that a liner can be applied to the bottom and stucco wall only? Leaving back rock wall exposed, except where the liner is cemented to the corners... <No, not really. Ideally we would have had this "conversation" before your actual construction... and hence you would have used a liner behind the rock work... it would have functioned as a "skin" a first waterproof barrier... Neither stucco or "cement" are waterproof...> If a partial liner covering (1 side wall with a liner) is not possible then my only option is to resurface the stucco side that failed. <Mmm... again... at this point, maybe applying a liner over the existing work, re-applying new stone over this...> A local "handyman" quoted $475 (labor only) to remove lose materials and re-surface one wall. That seemed high. <Not to me... but this would also fail in time...> I read about a product called Mulasticoat? It appears to be a do-it-yourself user-friendly product (no special tools, easy to apply). <This too will likely not last for long...> So... Advice please... Is it Liner or Re-coat? Do it myself ("average common-sense-handy") or do I bite-the-bullet and have a professional do it? Thanks Howard S <IF I were still actually "in the biz" (instead of just an easy chatter re) I would definitely ONLY do this job with applying a liner... as if the existing basin were just a hole... To be sure of integrity. Bob Fenner>

Pond Construction problems. Hello, I am Jim Garrett and a construction management major a Western Carolina University and doing an internship this summer and a problem has arisen with a pond and waterfall at a residential site development. I have monitored the water level and there has been a slow leak. The pond has no liner but was constructed with a product called Klingstone 400 manufactured by Klingstone Inc. of Waynesville, N. C. This is a polyurethane product and the landscapers were injecting under this hard surface plastic with more urethane that reacts with water and expands to fill the voids that undermined with more leakage. <Mmm, I would have used a liner... cheaper, more dependable...> We are at a point of trying to decide what to do about this situation, should we tear it out and start over with liner. The owner would like to see a 20 year product. Do you think this can be salvaged? <Possibly... depending on what the basin/s look like, how much "through-put" material there already is... if the plumbing can be laid in a new bottom, you might be able to treat the current construction as "just a hole"... and re-build over it with a liner...> I would greatly like to speak with you on the phone. My home # is 828- and I leave recorder on while at work, and my cell # is 828-. I would gladly call you back. This project was started back in April 04. We get water from a nearby river, and right now we are considering bringing water through a 2" line from a creek approximately 1500 feet for elevation and to reach the top of the water fall that would add to volume, present pump is at 135 to 140 GPM. Owner wants more volume for more visual effect, this waterfall and pond is at the entrance near a covered bridge that was built across the river. This is to be a grand entrance for the development in the Appalachian Mountains. If you could help me in anyway I would sincerely appreciate it. Thank you for you time. Sincerely, Jim Garrett. <The pumping issue is of course a separate item... When/if you re-do the basin/s, you might want to up-size the plumbing or add another two inch ID line... to get the flow you list... I hope you have a two speed motor... can be rigged with a timer or maybe a visual switch to turn on to the higher rate for a time... save some real money in the long haul. Am out at our place in Hawaii till the end of month... but can/will e-chat with you re this project if you'd like. Bob Fenner> James Garrett

Cement pond repair Dear Mr. Fenner, I am a park ranger for the County of Orange, with responsibility of Arden-The Helena Modjeska Historic House and Gardens. We have two ponds at the park, both are historic. Diameter is about 14 ft, depth is about 2.5 ft. see the attached photos. <I do> One leaks, one does not. The ponds are historic and on the grounds of a National Historic Landmark, one of just two in Orange County. For those reasons, I want to proceed with caution and be as minimally invasive as possible. <Understood> A previous ranger emptied the pond to clean it, left it dry for a while in the hot summer sun, which I believe caused the seal on it to shrink and cause leaking. After refilling it, it began leaking, a couple inches per week. Once again, last January, he emptied it, left it dry for a couple of weeks, and the leaking increased. It has now been empty since Feb. I have no records of how it was sealed by park staff prior to 5 years ago, but I do know it was sealed. <Okay> Some people have recommended using Mulasitcoat, and of course, I have read the link you provide, suggesting Thoroseal http://www.wetwebmedia.com/PondSubWebIndex/thoroselart.htm http://wetwebmedia.com/PondSubWebIndex/concrepart.htm. Others have suggested lining it, then adding a new coat of cement over the liner. If possible, I would like to avoid such extensive work, however I realize a quick fix is not always a long term solution. <Yes> Can you advise me in any way? with appreciation, Diane Wollenberg, Park Ranger South County Historical Facilities <It appears you have well-considered your two principal options here... In the face of fact that this basin is not leaking very badly, that it is of historical import, I would first try the coating route... following the manufacturers installation instructions to a "T". This will likely involve a thorough cleaning, possibly a bleach and/or acid washing (an action plan for this is archived on WWM), drying, mixing of the repair coating with a "mixing bar" and drill motor... and simply application with thick brushes. I do believe that due to the age and apparent massiveness of the constructs that this repair may do the job here. If not, a liner may be retrofitted as you say. One last concern of mine is to encourage you to pressure test the plumbing lines (if any) to assure that the leak is not to be found there instead of the basin. Bob Fenner>

Concrete pond leak Hi, <Hello there> I bought a house with a Koi pond about a year ago. This pond has been leaking and I think the problem may be getting worse. Without turning on the pump, the water level drops 1-2 inches a day. <Yikes> When I turned the pump on, it drops about 5 inches a day. Someone replaced part of the pipe (the piece that exits the pond connects to the pump) already and I think it leaks even more after that. I was told by the guy who replaced it that it was one single piece and therefore the leak can't possibly be from the new pipe. <Mmm, not so... but in almost all cases it's not hard to install a temporary plug and pressure test the line/s. You can have most any pool supply co. do this for you if you'd like> I have to hire someone else to fix the problem once and for all, but I don't know whom I can trust. The guy I am thinking of using told me that I should just reroute/replace all the pipes and reseal the concrete. <This is one route you could go> He also said that the pipes used should be a white PVC pipe rather than a black PVC pipe which is what's currently in place. <Mmm, the black pipe is likely ABS, not PVC... if the installer used a mix of these two plastics... or the wrong solvent on them...> Do you agree with what he is saying? <Possibly... I would like to see a diagram, a drawing of your basin/s and the actual plumbing schematic... have you read through my old articles on pond repair posted on WetWebMedia.com?> What kind of material would you recommend for resealing/recoating the concrete basin? Or do you have someone that you can recommend for doing the repair in San Jose, CA? Thank you very much. Y.T. Lan <I don't know of anyone in your area, but would interview folks/companies listed in your "Yellow Page" directories under "garden ponds", "water features"... Do please read here: http://www.wetwebmedia.com/PondSubWebIndex/concrepart.htm http://www.wetwebmedia.com/PondSubWebIndex/thoroselart.htm and the associated FAQs files (links in blue, at top). Study until you feel comfortable making a decision on how to go here. It may well be that using the current basin/s as a hole, applying a liner over them, with wire and concrete, laying new plumbing within this structure... is your best route for effecting a permanent repair. Bob Fenner>

Concrete Pond In Philly Ladies and Gentlemen, We have 50 year old pond, concrete, in Philly that the top 1/2 leaks - the pond is 8 x 5 x 2. Apparently, the top half of the sides leak because the bottom, is fine. What is the best medicine to fix this problem? Thanks, WE <Best to treat the existing basin as a "hole" and build another liner-based pond within it. Please read re here: http://wetwebmedia.com/PondSubWebIndex/concrepart.htm Bob Fenner>
Re: Concrete Pond In Philly
Dear Bob, Because of the size and shape, using a rubber liner within the concrete box would look a little too chintzy. Thanks. WE <I would use a/the liner with chicken or stucco wire over it... and shotcrete or hand-pack small grade (3/8 inch nominal) concrete over/within this. Coloring the material as you wish. Bob Fenner>

Leaky Pond >We just put in our pond a month ago. We seem to lose 2 inches of water within 24hrs of filling it. This presents problem because it brings the water level down past where the skimmer needs it to be. >>This is definitely a problem, not to mention wasteful. >The liner is new and we have been tearing it apart trying to find leak. Do you have any suggestions on trying to find the leak? Someone said milk but don't understand how that is supposed to work. >>Me either, how much milk would you use? And, would 1% be alright, or should you use whole milk? What about cream? This is all assuming that, should the leak be at the very BOTTOM of the pond, you have x-ray vision with which to see the milk or milk product leaking underneath. >Any other suggestions for identifying the water loss? >>I experienced something similar with our little pre-fab here at home, and what had happened was that the waterfall outlet had somehow shifted such that it was allowing water to splash enough so that it was basically emptying the pond. Other than that, I would be obliged to empty the pond, and test the liner itself, not a fun proposition. I'm a bit better at identifying air leaks (especially having a swimming pool). Marina >Thanks, Debbie Wilkins

Leaking Pond I've a small pond by US standards, but nothing in the UK is as big as you can do it ! <no... worries, perhaps we have nothing so charming as a quaint English garden pool <wink>> There's an upper pond of 600/700 gallons and a lower pond for the pump with a dam/waterfall - about 9" drop - dividing the 2. Its 4 years old. The construction is heavy duty builder's polythene as a liner, with crazy paving type stone set onto that in a thick mortar bed. Unfortunately I appear to have got one end of the 'dam' slightly wrong as it leaks slowly there (4 gallons a day I reckon) - the small area of flower bedding there is meant to be a wet garden anyway so the plants are OK but the loss rate is higher than I would like. I've got 2 choices I think - the first is to build more stone into that area to take out the leaking corner, or alternatively paint the stonework in that area with some sealant. Can you comment on that - the questions are what sealants are available, and/or if I was to build in the corner, how can I do it without disturbing the pond-life (4 Koi, etc), and what would I use as a mortar. Regards and thanks Rob Graham Edinburgh, Scotland <alas, my friend... any solution that I can think of does at least require removal of the livestock for safe repair. I must admit, from what I can gather you do have a bit of a quandary. The problem is actually a limitation by the plastic liner. Even set thick, the mortared stone cannot be trusted to make a long-term seal in either of out climates (I am in Pennsylvania, USA). Even a gentle shift of the earth from freeze/thaw will crack the mortar bed in the short term (less than five years as you have noticed) and require that the liner hold its own. Unfortunately, the Polyethylene liners are somewhat brittle and not very long lived even with a sturdy underlayment. I'm afraid that I cannot offer you a long term solution short of reconstructing the pond with a thick butyl rubber liner and sturdy underlayment. Assuming that you can find the leak, flexible sealants will only work for 6 months to 2 years at best. Epoxies require that the painted/sealed vessel/substrate is perfectly still/does not shift. Quite frankly, the least expensive and least laborious solution would be to temporarily remove the livestock, drain the pond, drop a new liner in on top(!) and dress the top edge as necessary/desired. It is better than gutting the pond for reconstruction or having to repair it three times in five years more. Best regards, Anthony>

Aquatic Gardens

Ponds, Streams, Waterfalls & Fountains:
Volume 1. Design & Construction
Volume 2. Maintenance, Stocking, Examples

V. 1 Print and eBook on Amazon
V. 2 Print and eBook on Amazon

by Robert (Bob) Fenner
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