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FAQs on Liner and Concrete Pond Construction

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by Robert (Bob) Fenner

pond mortar     6/13/17
From searching your posts I have found the following two recipes for waterproof concrete and mortar. Can you please help me decide which is best to use. I am building a small pond to hold 400-550 gallons of water. I will be using extremely large river boulders as large as a washing machine to frame to pond. I will be setting down a liner with stucco wire/concrete mesh/chicken wire like you described. I want to build as I go, having the pond be primarily built from large river rock (basketball sized to softball sized).
Question 1: Which concrete recipe or mortar recipe should I use?
Recipe 1:
3 Aggregate (1/4 pea gravel)
2 Sand (sharp)
1 Cement (plastic cement)

Recipe 2:
4 Aggregate (1/4 pea gravel)
2 Sand (sharp)
1 Cement (plastic cement)
<I'd go with recipe #1, less aggregate... Three parts here will be enough>

Question 2: Is there a foundation coating, cure retardant or additive I should use that will not change the color too much of the natural stone (clear coating is ok, shiny is ok, white is not ok).
<Mmm; no coating... mask off (paper or trash bags, tape) and try to not get too much cement/concrete on the rocks... sponge (large yellow ones at the concrete place) what you can while it's still wet... read on WWM, elsewhere re acid washing to remove the rest after all is set>
Question 3: There is not a home depot or Lowes around me that sells “plastic cement”, I live at 10,000 feet in Colorado. Can I make my own “plastic cement” somehow?
<Mmm, well; you can/could add plasticizing materials (such as limestone, hydrated or hydraulic lime); be careful with the last two (wear a breathing mask, gloves) as they're very alkaline...>

Question 4: There is one concrete producer an hour away that sells a “shotcrete” mix with the option of an additive mesh of some sort…would this work?
<Yes... but this term refers only to the fact that the blend is intended to be applied by high pressure...>
Thank you,
<All these types/kinds of concrete will work for you here. I suggest putting the liner and wire down... having friends over to help mix and apply whatever you end up with. Take your time. Bob Fenner>
Re: pond mortar     6/13/17

Wow! Thank you! I looked to see if just hydrated or hydraulic lime was available and no, it’s not. I have only used pre-mixed mortar in the past but I want to use your recipes and advise.
Question 1: Would this mix below work for the rock work I explained or should I add more less of something?
<Let's see...>
5 gallons of water (give or take)
18 shovels of aggregate/sand (I have sand from an old river mining operation. It is bank run dirt, washed and classified to half an inch, therefore everything in the sand is half inch and smaller) Would this count as my sand and aggregate both or just sand?
<Better to have sand AND aggregate... and for such a small pond/basin, "pea gravel", nominal 1/4" diameter. Half is really getting to be too big. IF you can, you want to keep the wall thickness down to 3-4"... easier to do w/ smaller grade gravel. The mix ingredients are overall okay... again, see y/our prev. email for relative volumes. 3:2:1, and just enough water for slump>
Another option is that I buy pea gravel and crush some rocks in a rock crusher (I have plenty of large rocks to crush)
<Yes... or likely easier (what I would do), sieve out the too-large bits, use them elsewhere (as in a mix for falls...)>
<And you, Bob Fenner>

Protecting liner in a pond from hoofs and claws     8/28/13
Hi, Bob.
Included below is our e-mail, in which you provided very useful advise <advice>.  Thanks!  I am still planning, and have more questions if you would please advise.  I have by now seen a raccoon getting into the pond from under the thorny miniature holly putting his clawed paws on the nearly vertical pond wall as he slithered to the bottom (and puncturing it on the rim of the pond when pulling himself out at the opposite end).  So I will have to cover all the liner with concrete, preferably waterproof. 
1.  Making the concrete waterproof; I read that mixing equal amount of Quikrete and Thinset is a good idea?  Is it?  Do you have  another, better suggestion?
<Mmm, am a fan of using welded mesh (cleaner the better; fave is stucco wire, but chicken wire will do... tied to... Please do just read here: http://www.wetwebmedia.com/PondSubWebIndex/conclnrconstpd.htm
and the linked files above>
2.  How to keep concrete from sliding down from the walls when applying it:
<As the above citation... working it into the wire mesh, perhaps adding a bit more alkalinity...>
Would 3/8" to 1/2" hardware cloth solve the problem?  Do I lay it over or under the chicken wire?
<Ah yes... the smaller mesh over the larger>
3.  Sequence of applying the concrete:  Do I put concrete on the bottom first, let it set a bit--how long, to what firmness--and then build up the sides--waiting long enough to be able to crawl over the bottom on boards without ruining it but not too long so the old and new concrete will bond.  (I would wet the side of the setting concrete to help the bonding.)
<Get help; concrete overshoes... olde clothes; start early in the day... TAKE YOUR TIME... This is VERY HARD WORK. The concrete can be applied w/ pressurized air (shotcreted) or hand applied by  pushing it up the sides... in a systematic fashion>
 Since there are bushes around most of the pond (some very thorny) I cannot kneel outside of the pond and put concrete on the walls. Can I put a board on the partially set concrete on the bottom, kneel on it and work on the sides? 
Will the seam safely bond if the concrete on the bottom is only partially set?
<Not really; and not really necessary that it does. Best to avoid (cold joints) though just the same>
4.  The water at the bottom of the waterfall will be about 16" deep.  Would it eventually erode the concrete?
<Not for many, MANY years. Decades to centuries>
Should I put a large stone on the bottom where the water will hit the bottom?
<If you'd like>
Many thanks for your answers.  Best regards, Zuzana Dillon
<And you for your sensible questions. Again, do get help... do on a cool day; start in the AM... Have friends who have done concrete work assist. Bob Fenner>

Concrete Pillars     8/3/13
Hello, doing pond expansion (30 x 30 x 3' deep) and need to put short dock type platform out to put lights on
to shine on falls coming into. Was thinking of 2 concrete pillars set on liner bottom poured in place with sono tubes 12 inches in diameter. Would this amount of concrete mess with ph levels? Thanks Bob
<Can; yes... I'd make at least the part that will be underwater w/ plastic cement rather than Portland... give it a spritz of ten parts diluted Muriatic (then 0.3 M HCl) to leach out most carbonate exposed, and consider even coating it with your fave foundation prep., plus colour. I'd also first cast some footings for these pillars (2 X 4's or sixes will be fine... in a box type arrangement), with some small rebar upright to tie all together. Do send along progress pix please. Bob Fenner>
Re: Concrete Pillars     8/4/13

Thanks for info. How big should I make the footing?
<Mmm, something like two by two feet>
Also should I put Like a rock mat or something like that under the footing since it is being done on top of the epdm liner to help cushion the weight?
<Oh! Yes; for sure... a couple of pieces of carpet (remnants) are highly recommended. I had assumed this basin had or was intended to have a reinforcing mesh/shotcrete barrier. Do read here:
and the linked files above>
Most all of the pillar will be in water.
<Ah yes; BobF>
Re: Concrete Pillars     8/6/13

Hi Bob, well I can say our Home Depot, Lowes and 3 other lumber building stores do not have plastic cement. So I figured I would Contact Quikrete direct, so I sent off email,11/2 days later still no response. So went back to web site and got phone number for Quikrete northwest division,called,told
them that I had questions on amount of gravel to add for pouring my 2 pillars and also how many bags it would take to do the job since this is going to be a special order IF they even have it in the Seattle area warehouse, the guy on the phone goes ooh,your going to have to talk to one of
our specialists,I'll transfer you, guess what voice mail, gave him 2 hours called back same thing all day.  So I hate to bother you again but is the product I need a 2121 plastic cement by Quikrete? 
It/this will do; but mixed with more than sharp/Silica sand... I would use 3/8" nominal crushed rock... You can just use a low - alkali/ne concrete mix of any available type. Bob Fenner>
Thanks again

Protecting flexible liner from (deer) hoofs and claws    7/14/13
First of all, thank you very much for your very informative site.  Could you, please, confirm that the process outlined below would be the right "recipes" for protecting the liner in a 8' diameter pond from hoofs and claws, and answer my questions?
Sixty percent of the pond's perimeter are surrounded by thick bushes and have steep sides with a shelf for plants or large rocks to-be-partially submerged--unlikely that sharp-footed critters would get in the pond there.
 40 percent have a fast sloping "beach" bordered by a lawn where they are likely try to enter. 
I am thinking about covering the beach and the pond bottom in the shallow part of the pond with chicken/stucco wire (laid directly on the liner) and about 1" of Quikrete post mix (suggestion from your web site) and thickly press into the Quikrete round pebbles and mid-size round stones.  The remaining stones will be scattered over those imbedded.  Should I lay something on the liner before putting down the wire in order not to puncture it?
<No; no need to lay something over the wire. DO take care to not introduce sharp (ends) of the wire into the pond itself. IF thus a small area is to be wire/concreted, use both ends of the roll of wire (that are terminated, not sharp wire-ended) to end in the pond itself... with the cut wire-exposed parts out of the pond... in the walk area OR attached to re-bar as we show in various articles on liner ponds on WWM's Pond subweb>
 And if so, what?  Given that stones will be in the Quikrete, is 1' layer sufficient?
<Likely so... IF the liner is set on/over original grade (so it doesn't flex, allow the concrete to crack though it's only an inch thick or so)>
  (I am trying to save my back as much as I can!)
<I do understand; and agree>
 Does the job have to be done all at the same time before the previous Quikrete patch fully sets?
<Mmm, yes; all contiguous/connected concrete must be done at the same time>
  I would prefer mixing the Quikrete in a 20 gal pail,
<Mmm, no; either use a wheel barrow or purposeful concrete mixing "tub" (see the Net re or a large hardware store), AND a short handle flat end shovel (am not a fan of "concrete mixing hoes")>
start in the middle of the pool and work in batches in the direction toward the beach and spread the work over 2 or 3 days.
<Must be done on one day... get some help. Much more fun... and do color the concrete. See the hardware store folks re this as well>
 Since there is a liner under the Quikrete the seems between the batches do not have to be watertight.   Did I miss something?
<Will be MUCH stronger done as one piece... one day>
 Do you have any other advice?  Thank you very much in advance for your answer.  Zuzana
<Keep gathering information, tools, materials... Is there a "pond" or "Koi, goldfish" society in your area? I'd contact them re helping here. Do take your time in planning. Bob Fenner>
Re: Protecting flexible liner from (deer) hoofs and claws    7/14/13

Thank you very much for your quick and informative answer.
<Am glad to help you. I had a friend whose pond years back was decimated by a visiting Cougar/Felis concolor, that left huge scratch marks in the concrete that had been poured over the liner in the ceremonial entry/exit area of his liner pond.... My solution to him to discount such depredation?
To put out a large tray of food!>
 I will try to get help as you suggested, and I do have an old wheelbarrow that will be ideal for the job. 
<Ah good (I have two!). Much easier on our backs, and a relative breeze to wheel over to the area to be applied>
Again many thanks and best wishes to you.  Zuzana
<And you, BobF>
Re: Protecting flexible liner from (deer) hoofs and claws    7/15/13

Hmm...  I did not even consider cougars!  Where did your friend live?
<Here in San Diego; La Costa... by chance next to Gene Roddenberry of Star Trek fame... the combo. driveway had a neat model of "Enterprise" as his/Gene's mailbox>
  I live on the northern edge of the Olympic peninsula and we do have cougars, although not in my yard (yet).  Perhaps the cougar could feast on the deer that wreck havoc in my garden and I would not have to spend money on fresh meat for the cougar!
<Heeeee! Ah, the/a great circle of life. Cheers, BobF>

Concrete Pond Project 7/31/11
Hi Robert,
I read most all of the articles you wrote on wetwebmedia.com pertaining to concrete ponds. After reading what seems like hundreds of articles on the subject I found yours to be far more helpful than the rest.
<Glad you found it of use>
I plan to build a good sized water feature on my property and want to go with a liner underneath concrete for reasons you pointed out in your articles. Most of the people I've talked to try to sell me on just a liner but it always seems like a flimsy way to do it and I like the look and rigidity of concrete. In your article 'Building Concrete & Liner Ponds' you mention 'In our neck of the woods in Southern California' which is where I live as well.
Do you offer consulting or could you point me to someone you feel is good at this?
<Mmm... there may be some of these folks still about... Do try here: http://www.rockandwaterscape.com/contactus.htm
Thanks very much,
<Welcome. Bob Fenner>

Attaching a liner 6/4/2011
Hello I am building my first pond. It is made from concrete blocks. I do not know how to attach the pond liner to it. I have attached a pic.
Thanks in advance.
<First of all... very carefully. Important that you warm up the liner, lay it in, fold it ever so evenly so that the corners are not too "bunched up"... then to overlay into the cinder block walls and fill the pond... trim the liner inside the front edge of the blocks and about half way into the side... such that there is room for the cap stones/pavers/covering material over the existing blocks traps and holds onto the liner edge.
Understanzee? Bob Fenner>

New pond construction, concrete/alkalinity issue -- 3/3/10
Hi, I'm currently building my first pond and have been following a plan I found in a book. I dug the hole 19 ft x 8 ft x 21/2 ft ,
lined the hole with geotextile & butyl. I then made a concrete collar on the liner all the way round on the planting shelf and built a three course brick wall on top of that with engineering bricks and mortar. It was not long after completing this stage that I found out that lime in the concrete and mortar was poisonous to fish,
<Can be... there are some not-quite-so toxic cements available...>
I bought a fish friendly silicone sealant and sealed around the joint between the liner and the concrete collar
<Mmm, these rarely work... Okay, never to my experience>
and bought G4 to coat the concrete and bricks, however after 10 days or so I filled the pond and have water filling up the wrong side of the bricks and leaching out lime. Of course the water doesn't leak out to the soil because the liner comes up to the top of the bricks, my question to you is, will the leaching stop with various drains and refills,
<Mmm, yes... in time... I would do a couple of dilute acid washes (HCl...) as gone over on WWM... to speed this along>
will the bricks last submersed in water or should I put another liner over the top of the construction.
<I wouldn't... unless you're in a "big hurry", the better part of the alkalinity can be dispensed with in weeks to a few months>
Also I intend to fix rocks to the inside edge of the pond from the planting shelf up to hide the liner and at one end have a waterfall trickling down over the rocks. These were going to be mortared to the brick work, now I'm worried about lime how should I fix these as it may be difficult to coat mortar with G4 between rocks. Your help and any suggestions would be greatly appreciated.
Regards Steve
<Look for and use "plastic cement" here Steve. Much less noxious. Oh and do read here:
and the linked files above, and here:
Steady on, Bob Fenner>
Re: New pond construction, concrete, Alk. 3/3/10

Hi Bob
Thanks for your reply, very helpful, just a couple of things, I didn't get an answer to whether the engineering bricks would last ok constantly submersed under water ?
<Engineering bricks...
Though made of a good deal of cement, these are much more chemically inert than the mortars commonly employed to cement them together. Shorter answer, these should be fine submersed>
and living in the U.K. I have never heard of plastic cement but I will research it.
Thanks again Bob.
Regards Steve
<Mmm, yes... may well be called summat else. I do see some listings on Google under the search string: "Plastic cement in England". BobF>

Curing a pond. 2/26/10
dear Sirs,
I have built a brick form pond that has been cement rendered. Sealant was applied to the walls it was built against and then to the brickwork, but not to the cement render on the inside of the pond. I have tried many ways to
reach a suitable ph level . I have filled the pond, cleaned the sides and base with vinegar solution and have added both vinegar and mild (30%) hydro chloric acid to the water. I have left it for a week or more and repeated the process. However, as soon as I drain and change the water the ph shoots up. The water source is a neutral 7.It is now over a month.
Any advice please
Anthony Sullivan.
PS I live in Malaysia
<Hello Anthony... how "high" is your pH now? If below 8.0, I would not be overly concerned... As you have already used vinegar/Acetic and HCl acids for washes, I don't think that more exposure will help much here, and
perhaps may lead to weakening of the cement (Next time less alkaline material). It is likely prudent/best to just leave the water in the system, try growing some easy plants (floating or emersed) for a few months, and you'll likely see a gradual lowering of pH here. Bob Fenner>
Re: Curing a pond. 3/8/10

Hi Bob,
Many thanks for your reply. The ph level was off the scale. I have now decided to tile the pond and it is now looking better. The ph is about 8 now after 3 days with water and running the filter.
<This may be acceptable. What life do you intend to keep here?>
Once again thanks for taking the time to reply to a stranger and if you are ever in Malaysia I would be glad to buy you dinner.
<I have been to, and am revisiting your country this summer (Kuching... in Borneo, then out to Mabul for diving...). You may see me yet! Cheers, Bob Fenner>
Re: Curing a pond. 3/9/10
I used to be the head of museums in Sabah.
<Ahh! I have likely experienced your work... in Kota.>
I built the largest and the best new purpose built museum in Asia. I know Mabul and of course Sipadan.
<And Kapalai, and many of the surrounding isles and mainland likely. A treasure>
I was at these island in the 70s.
<Wow! As you are very likely aware, Sipadan is "closed down"... to folks staying on it... though the military does more than live there; and many divers from M and K visit there to dive daily still>
Also spent a lot of time in the jungles and longhouses.
Met and worked with David Attenborough on numerous occasions and also Jacques Cousteau.
We now live in Kuala Lumpur and I run a game fishing business See www.hook-line-sinker.net or www.angling-malaysia.com
<Thank you for sharing. One/I always wonder whom the folks are who've done the sort of work you describe. Cheers, Bob Fenner>

Plastic Concrete over PVC Liner -- 08/26/09
I have a book on water garden design that has a brief section on using Plastic Concrete layer over the PVC liner. I am considering this for a new pond I am installing myself. I read your article about this as well, and
have a few questions:
<Go ahead>
The book recommends a 1 inch layer of plastic concrete with chicken wire mesh. Your article recommends 3-4 inches thick plastic concrete. If the concrete is for UV Protection, puncture protection, and aesthetics it would seem that 1 inch would be sufficient as cracks in the concrete would not result in leaks if the cracked pieces stay in place.
<Mmm, not really.. the concrete fulfills a few functions... one other is prevent puncture... a one inch shell will very likely crack... with time, folks walking on it, freezing weather...>
Note, I live in Maryland (no earth quakes to worry about) but my soil is sandy so could shift/settle.
I plan to do it myself (with a friend or 2) if it only needs to be 1" thick (need a little more than a yard), but at 4" that would exceed my capability to handle the materials (would have to call-in the cement truck and don't
know if Plastic Cement is available by truck in my area, it is not carried locally in the mega home improvement stores).
<Odd that it is unavailable... Is at all Lowe's, Home Depot's I've ever been to... Another poss. is for you to rent a small concrete mixer, and with a few friends, mix and place the concrete...>
Next question is when researching Plastic Cement by Quikrete, their spec sheet refers to an alternative material called Fiber Reinforced Stucco which is available sanded. Are you familiar with this material?
<Yes... is like their concrete mix, sans the aggregate>
Any issues, like alkalinity issues?
<Is much more alkaline than Plastic cement products... wear gloves if you have a sensitivity>
It might be able to be used thinner with few cracks.
<Mmm, again... not really>
Third, the book recommended 'chicken wire' in the 1" concrete. Your article
goes a little farther and specifies 3/4 inch "chicken wire", but I am
guessing that 3/4" is the mesh density not the wire diameter.
<Correct, the specification is the "gap" size twixt the twisted wire>
Chicken wire in my area is not something I find as a specific product,
<Can be called "wire mesh"... again, is at all HD's, Lowe's...>
more like a type of fencing material so I need some more specifics to see what is recommended. I am very concerned that I will puncture the liner when installing the heavy-duty wire mesh and concrete resulting in a leak that at that point would be very difficult to fix with liner under concrete. Is this a realistic concern?
<Can be... You just need to be careful when laying in the wire... the layers (comes in determinate heights) can be tied together (best with "hog rings") to prevent loose, spiky ends from flaling about...>
What wire diameter do you recommend for my do-it-yourself residential 1400 gallon pond?
<Either 3/4 or 1"... You can maybe sub "stucco wire" (sans the cloth) if other steel wire is unavailable>
It seems to me a plastic lawn/garden netting would be a lot easier to manage with less risk of puncture. Is this a reasonable substitute?
<No... the concrete won't "form" crystals about, making the shell, structure that much weaker.>
Tammy Faulkner
<Tammy, do look about... Craig's List, online directories, the Yellow Pages for folks with experience to lend you insight here. Bob Fenner>

Plastic Concrete? - 06/05/09
Greetings Bob,
I greatly appreciate the numerous articles and responses to questions that I have found from you as I have scoured the internet for a variety of information relating to ponds, pools and water features. I have a question regarding the use of plastic cement in fish ponds and waterfalls.
I have already completed excavation of a waterfall that leads to a pond. I've made a few of these in the past, and they all have been 'liner only' streams and ponds. I've decided to have this water feature utilize an EDPM liner, and then a concrete layer on top of the liner (first time for me w/ concrete for me). The liner is all in place, and I have supported chicken wire about 2.5 inches above the EDPM liner using hundreds of 2.5 inch cut lengths of 2' ABS pipe (the 2.5' sections are held in place using zip ties that attach the ABS pipe sections to the wire; single drill hole through the pipe works fine). I'm ready to start with the concrete (I'll be hand packing J), but have a few questions.
I had planned on using a Portland cement based concrete (3 parts aggregate, 2 parts sand, 1 part cement) for this project, but was in intrigued by a number of references to plastic cement on the internet and in some newer books on water features. I am pretty sure that I want to use plastic cement, but I am unsure as to whether I should have an under-layer of 'traditional' concrete (and then a layer of plastic cement), or if I should just stick to a structure that utilizes plastic cement alone.
<Just the plastic cement in place of the Portland>
I plan on an overall thickness of about 3+ inches; is this thickness ok for plastic cement?
<Yes... along with the aggregate (small sized... "pea"... nominal 1/4", and sharp sand, water... oh, and color/oxide>
My understanding is that a standard 'mortar' mix for plastic cement has about 4 parts sand to 1 part plastic cement.
<Yes... but I would add some aggregate... likely at least 1, 2 parts to the mix here... won't weaken, will improve the looks>
I was thinking about laying some plastic (thick garbage bags) over the cement as it hardens,
<Mmm... I wouldn't...>
and then placing the larger rocks on top of the plastic to make indentations that will later accommodate the rocks.
<Well... I would try to just mortar all in place as you go along... start from the bottom... and do your best to not make too much of a mess... use large "yellow sponges" and clean water as you work your way up... Not possible, practical to "pre-make" spots for the rock later... nor necessary for seal/leaking's sake due to the use of the EPDM liner>
Once again, I'm kind of thinking that a plastic cement (mortar mix) might be a good way to then fix the rocks in place (in the indentations made earlier). I initially thought I would use some sort of latex or foam sealer to fix the rocks in place, but I'm starting to think that maybe the plastic cement might do well for that also.
<It will... and is the route I would go... Have some labor/help there if this is a big job... to mix the mortar/concrete, help with clean up>
I also wonder if you can make concrete from plastic cement.
<Yes you can and should>
It seems that Quikrete's plastic cement is just Portland cement with latex additives,
<Mmm, yes... and this co. does have some cheap to better admixes, mixtures... but I encourage you instead to "make your own"... buy the big bags (90#) of plastic cement, and sand, aggregate, colour... and blend, mix yourself just ahead of applying>
so I thought that maybe using pea gravel aggregate would not only be esthetically pleasing, but maybe would give some addend strength to the overall project (I really don't want to have to redo this later on due to cracking J).
<No worries re in any case>
And if that isn't enough, I've also heard that a mixture of just plastic cement and water (to a paint-like consistency) makes a good sealer for concrete work.
Am I getting carried away with the idea of plastic cement?
<Not at all... is much easier to work with, less caustic... "prettier" as well>
Thanks very much, Dennis
<Certainly welcome. Bob Fenner>
Re: Plastic Concrete? 6/5/2009

Thanks very much for your response and suggestions; you have really cleared things up for me and I am excited to move forward with the project.
Once again, thanks - Dennis
<Welcome Dennis... this does read as a well-thought out project... Am sure you will enjoy the process and product. BobF>

Help, don't understand FAQ response -- 05/02/09
Just wanted a little clarification on this Liner and Concrete Pond Construction FAQ:
"Cementaceous construction inside biological ponds 9/7/05
Robert, Have sandy soil for my pond, have question about using mortar and flagstone on inside to make walls. Can the mortar be toxic to fish.
<Is to a varying extent, depending on make-up>
I have heard of a plastic cement but can't find any info .
Bill Oglesby
<Use of plastic cement/s is advised. Are less caustic, toxic... still better to lower level of the basin/s while doing, curing this work. Bob Fenner>"
When he built my sunken pond, the builder dry-stacked cobbles over the liner. The walls are quite steep and the cobbles slump. I'm tired of restacking them every year. I want to cover the liner like Bill proposed
here. I don't understand is Bob's comment, " . . . still better to lower level of the basin/s while doing, curing this work." What did Bob mean?
Thanks so much - really appreciate your help.
<Gosh Carole... though I wrote this, I don't "get it" either... Is there more? I don't find the original you've copied here in:
Will you please check above and below this clip and see if there is summat more that will help me put in perspective? But, to respond to your question, yes to putting in some reinforcing mesh (and mortaring in
permanently those cobbles. BobF>
Re: Help, don't understand FAQ response -- 05/03/09

You are fantastic! Here is the link - item is about half-way down:
thanks again
<Oooh... I think I " get it" this AM... Am encouraging, cautioning the writer to lower their water level to prevent contacting the new mortar (with their permanently placing a flagstone berm/edging), rather than
leaving the pond basin filled all the way to the top. It will be necessary for you to drain your pond completely... and hold your livestock in quarters for a week or more elsewhere. Cheers, Bob Fenner>

Pond building, liner ap. 7/9/08 Hi hope you can answer my question I have a sunken garden pond 11'x6'x3' which is home to around 12 fish including 4 showas and 2 19"+ orf's. The thing is i want to build a raised pond standing on a hard standing patio i have which measures 23'x18'x10", half of which is taken by my decking. The pond i want to construct a pond 11'x6'x3.5' with a liner, would this hold on the concrete. thank you <Mmm, better to best to "finish" the shell... a monolithic cast of concrete? Or block... and "trap" the well laid in liner in a cap of some devising... can be formal... or mortared rock of some sort. I would NOT try to stick/adhere the liner to a structural wall, base... Best to use liner type, thickness as per: http://wetwebmedia.com/PondSubWebIndex/Pond%20Sub%20Web.htm the second tray... "Liners..." fitting through puts (drains, returns...) loosely with some liner around them for movement... Bob Fenner>

Sealing toxic effects of hydraulic cement 10/19/07 Robert, <Dana> I read with zest (and hope) your articles, FAQs, and related links regarding leaky ponds, but I could not find a solution to solve my dilemma. You're probably going to laugh hysterically when you read about my problem but here goes... We have a very old and small (<500-gal.) above-ground fish pond. Three large goldfish and one river perch have called it home for years. It's base construction is river rock, concrete, and a thin coating of Gunite (leftover from an in-ground swimming pool installation). We used to run a 3/4 hp pump for circulation but over the last few years the pond lost so much water daily that we no longer had to aerate the water. <... for 500 gallons? I'd very seriously look into more/modern pumping here... Will save you a bundle in electrical cost> We let a garden hose trickle into the pond to replenish the water. [Are you smiling yet?] Anyway, we were recently given a large supply of left-over building materials, including about 80 lbs of Quikrete Hydraulic Cement. Sooo, you guessed it, we lined the entire pond with hydraulic cement. Yes, you read correctly, the entire pond was meticulously hand-lined with concrete plugging material. [Are you laughing aloud?] It should be waterproof, yes? <Hopefully... if the basin itself is not "moving", badly cracked...> My dilemma is this... we want to neutralize any toxic effects of the hydraulic cement by applying a safe non-toxic top coat or paint. Therefore, please recommend a suitable Thoro product. Do you think their waterproofing paint would be safe for the fish and sufficiently block any toxic effects from the hydraulic cement? Please advise. <Mmm, their Thoroseal should do it... You can color this if you want... with an oxide/coloring agent... available most everywhere. Though will be about what it's going to be in time with algal growth> Many thanks for your invaluable information. Dana <Welcome. Bob Fenner>

Concrete pond specification 6/25/07 Dear Sir, I am about to undertake a pond project.. If I can give you a bit of background to the situation you could possibly advise if this project would be viable and assist with the technical specification to make this possible.. Having recently purchased a building plot we uncovered a former bomb shelter under what we thought was a mound of earth.. Now with house complete and ground works underway we are about to embark on the pond.. What we have done is take the top of the shelter with all debris pushed inside to create a base. What we have now is a structure 4.9mts x 2.4mts with an undetermined depth..(4brick thick at ends 2bricks thick at sides) My thoughts were to form base with 150mmsub base DPM and 100mm concrete to finish , line internally with concrete block, render and tank internally.. My uncertainty surrounds what materials to use with regard to waterproofing/ what size pump/filtration etc.. finished article would be approx 4.6mts length x 2.0mts wide x 0.75mts deep.. Any advice in this regard would be gratefully appreciated.. Dave Greenland <Mmm, well... there are a range of ionic-sold/non-elastic coatings one might use (cement "plasters" for instance) which are fine for "original grade", solid foundation applications... for vertical-sided, formal ponds... Some more elastic (e.g. chlorinated rubber based) materials... but I do encourage you to consider (moving all the way ahead to unreliable settings where the base may indeed move) to use a liner here... Please read: http://www.wetwebmedia.com/PondSubWebIndex/Pond%20Sub%20Web.htm the pieces in the tray under "Construction" re Liner Use. Bob Fenner>

Chemical impact from Gunite 12/1/06 We are having a pool built, the plumbing and Gunite are complete and the decking has been formed. We recently discovered or uncovered the dirt around the pool plumbing and noticed that Gunite has been mixed in with the dirt and is resting on and near the PVC pool plumbing. During this discovery someone told us that Gunite has a chemical that will eventually get into the PVC plumbing, contaminate the water and potential erode the PVC pipes. <Mmm... this is news to me... look up Gunite on the Net... is basically a very dry mortar of sorts... a concrete without aggregate and just enough water added/entrained to allow it to be "worked", accelerated to "stick"... is alkaline but not that corrosive...> Can this be true? I am concerned for my health and also for the potential damage to our decking surrounding the pool. <I would not be concerned here... As long as the Gunite underwater itself is "cement plaster coated" (to make it smooth and water-proof) there is no need to worry. Bob Fenner>

Cementaceous construction inside biological ponds 9/7/05 Robert, Have sandy soil for my pond, have question about using mortar and flagstone on inside to make walls. Can the mortar be toxic to fish. <Is to a varying extent, depending on make-up> I have heard of a plastic cement but can't find any info . Bill Oglesby <Use of plastic cement/s is advised. Are less caustic, toxic... still better to lower level of the basin/s while doing, curing this work. Bob Fenner> New pond, owner 8/21/05 Dear "Crew": <Jarvis> I just finished building a 220 gallon pond in my back yard, and is wanting to add Koi ASAP, I'm not sure what to do though. should I add any baking soda or salt? if yes, how much should I add? <... what for? I would test the water quality, at least pH, alkalinity and maybe add an inorganic acid to the water, or "wash" the sides down with a dilution of this... if the basins are new, cementaceous... alkaline. Please read here: http://www.wetwebmedia.com/PondSubWebIndex/conclnrconstpd.htm and: http://www.wetwebmedia.com/PondSubWebIndex/acidblchpds.htm> should i but any water testing kits? <Yes, I would. : http://www.wetwebmedia.com/PondSubWebIndex/tstkitspds.htm and the linked files above... Bob Fenner>> thanks: Jarvis

Pond construction... mainly 6/31/05 Just recently we added a cement pond to our back yard. And before putting water into the pond I need to know what measure should be taken to prevent leakage. <...?> A few question I have is how long should I allow the cement to cure before cleaning it with a solution? And what type of solution should I use? Thanks for your help! Diamondmind <The basin/s shouldn't leak if they've been constructed properly... some folks seal concrete with a coating that aids in protecting the material and rendering it less likely to affect water chemistry. Most installers use an acid wash to reduce alkalinity... some people just utilize vinegar here, but professionals often dilute Muriatic (3M HCl) and brush this on, rinse, pump out... These issues are covered on WWM: http://www.wetwebmedia.com/PondSubWebIndex/Pond%20Sub%20Web.htm You might avoid a good number of future issues by studying now... Bob Fenner>

Pond Construction Sat, 2 Apr 2005 Greeting, I have been reading several of your excellent articles on the web. I am looking for specifications for a pond with a concrete (or Gunite) topping over a liner. <Specifications? Your installer (I strongly suggest "going Union" here) will know what these are... depending on depth, slope... if you're going to "plaster coat" the Gunite (I would with something)...> I also need an installer for a client in the Palm Springs (Indian Wells) area of Southern California. <Mmm, I'd consult the "Yellow Pages" under "Swimming Pool Construction"... get at least three bids, talk with whoever they give you references for their recent work> I would appreciate any direction or references that you might have. <Unfortunately it's been many years since doing actual jobs in your area... but there are likely still a few excellent companies out your way... There are MANY pools and water features out that way as you no doubt are aware. Bob Fenner> Rick English English Pool Consulting

Waterfalls and mortar Bob, I am building a waterfall for my fish pond and would like to use mortar to set my rocks onto the liner so the water will go over the rocks instead of under them. I am concerned about the mortar leaching out into the pond. Is there anything I can do to the mortar to prevent this? I've tried the black biofalls foam and found it very difficult to work with. Thanks, Gail <Yes. Make sure and use "plastic cement" in your mortar mix... much less alkaline than "plain" Portland cements... Mortars are just cement, sharp sand, water and possibly a coloring agent... and easier on your skin in working with it as well. Bob Fenner>

Pool slide I have just shotcreted my pool and in ground slide. Do I need to brown coat the unleveled areas and rough spots before Thorosealing the slide or will Thoroseal fill in all these voids? <Not unless the current surface is very rough> Will Thoroseal provide me a smooth sliding surface; <Not enough to likely suit you> if so, how do I achieve this. Do I trowel it on or use a paint roller or brush? That you for your response. <Look into smooth mortar "plaster coating"... can be done by oneself... but if this job is very big (like a swimming pool), better to have professional "pool plasterers" trowel it out. Bob Fenner>

Acid wash acid for ponds Hi I just read your article on Thoroseal I just used it to reline my Koi pond you mentioned a light acid wash before introducing live stock What product can i buy to do that. Thank-you for your time Danny Fitzgerald <Hydrochloric, as three molar concentrations sold as Muriatic Acid is your best bet here. Sold in swimming pool supply shops, concrete et al. businesses. Please read here re doing such acid washes: http://www.wetwebmedia.com/PondSubWebIndex/acidblchpds.htm and follow carefully the cautionary remarks. Bob Fenner>

building concrete pond??? Robert, <Jim> I am constructing a pond with the inside dimensions of 6 x 10 by 3 deep. I am planning 6" wall and floor thickness. It will have a 3" bottom drain line and a set in concrete wall skimmer, like a pool. <Do make the "casting" around this skimmer assembly a good six inches thick all the way around as well> The walls (sides) are vertical 90°. I have a few questions and am hoping your experience will shed some light on them. <I'll try> 1. I am using a 6-1/2 bag mix with ipanex admix for waterproofing and will plaster the inside with black plaster, is a liner still needed.? <Not needed... but good/worthwhile insurance... especially in areas where the ground moves (earthquakes, freezing...)> 2. I am tying rebar and will hang the inside wall forms as one 4 sided piece (suspended 6" above the floor. <Make this 3" on your stand-offs... cast in about the middle> Can I pour this all at once, floor first then walls....or will it try to seek it's own level. also do I need a vibrator wand for the walls (trapped air).? <Best to pour all at once... the floor first... how are you forming up the walls? If they are vertical... are they being molded somehow?> 3. If the slump is low enough can I just pump the walls starting at the bottom and building then vertical. or will it all sink without a form. ?? I hope this will work. <Not exactly... even with an absolute lowest slump the mix will compact, compress> 3. Don't I need a hydro-static valve in the bottom drain to protect against the pond raising out of ground when emptied for maintenance.????? <Yes! Or other provision...> I would love to use Gunite except the job is too small. <Mmm, not necessarily too small... Have you checked with the pool sub's in your area? Do take a read through the "Pond Index": http://www.wetwebmedia.com/PondSubWebIndex/Pond%20Sub%20Web.htm re construction methods on our sites before actually initiating construction. I encourage you to go with an underlying liner, and for us to chat re the forming of the walls, bottom of the system. If your design calls for vertical walls, either reconcile yourself to making them of block or forming them with plywood and snap-offs... Let's keep chatting if I'm not being clear. Bob Fenner> thanks Jim brown

Re: building concrete pond??? bob, thanks for the assist. a ready mix co. quoted $370 for the concrete and $170-$200 for the pump... <Mmm, about right> check this ! today got 2 replies from Gunite guys, one at $1,600 and one at $1,900. think I will stick to working out the pour version. <... the difference isn't as much as you might think here... the pour option includes having to hand-pack, move around... even with the pumper, about seven yards of concrete... at about 2 1/2 tons a yard... yes, about 35,000 pounds of material... so, you'll need a few friends, for a few hours... the Gunite folks will probably finish the shooting, leaving you with only cement plaster coating to do... something (my back's starting to ache) to think about> I think your right about the liner. I will sketch my idea of the form for the pour and .PDF it to you early next week. got a lot of rebar to do this weekend. <Real good... the progress will be well worth it... and give you a much better idea of what you're up against. Bob Fenner>

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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