New pond construction, possible problem with mortar?


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Hi all, I'm in the last stages of constructing a natural fish pond and have a possible emergency!! I hired the contractor who recently finished our almost 2 yr whole house renovation and while they have experience building a waterfall, they have never built a pond this size. They've been wonderful, I gave them Robert Pavlis' book to read and they've watched all the videos I've sent them, regarding construction, etc. The pond is about 35'x50', 3-1/2' deep on one end, sloping to 2' deep on the other end, approx. 35,000 gallons, with an EPDM liner, no filter/pump as this is a natural pond. They added about 6000 gallons of water as they started to add the rocks on the bottom planting ledge. Everything was going great until the installation of "floating stepping stones" across the shallow end. They used mortar to secure the rocks to the supporting pillars and the excess mortar fell into the water. Two days later the water is still a little murky but what I'm really concerned about is the layer of 'silt' that has formed on the liner. Not only am I worried whether it will be safe to add fish, harmful to plants but also, we have 3 dogs who I anticipate will use the pond daily and stir up the silt every time they enter and exit the pond. So if it is harmful to the fish or plants, what are my options to remove it? I need to be prepared when the crew arrives tomorrow morning to give them instructions! Any suggestions are appreciated - thanks!
 
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I'm sure there will be an expert of 5 along soon who can give detailed answers to your questions, but based on what I'm expecting in my pond I offer the following. :)

Dont forget cement / mortar / will harden underwater, it may well do weird things to the ph. Not sure. The silt I think would appear to be be normal... I'm thinking this as there are plenty of pond build pics that have silt in the bottom.. I'm expecting to see it too.

Test strips. Colombo and others make test strips you dip in the water and it gives a chemical breakdown of water quality... my dogs are more than happy to roll, dig, drink from disgusting stinky muddy pools so as long as the test strips come up ok, I wouldn't be too bothered...

When to add fish is something I'll do after a period of time... at least a month I'm thinking but it will depend on what the test strips tell me...

I dont plan on using mortar directly onto the EDPM... so cant help there but I don't suppose you are the first to do it.. There is a post around here somewhere (or on google) that details a long list of chemicals and how they react with EDPM.. I remember that petrochem based elements were not a good mix but dont recall seeing anything about mortar being nasty... but there could be many other reasons not to.
 
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Thank you! I'm concerned for two reasons. We also constructed a small concrete fish pond adjacent to our house and the local water garden center recommended painting the concrete with Herco Pond Coating to prevent any contaminants leaching from the concrete that would be harmful to fish. So I'm assuming leaving this silt will more than likely alter the Ph and not in a good way. Also, in the past when working with concrete or grout on my mosaic or garden art projects, I discovered I needed to discard any water used in these projects as far away from the gardens as possible. When we had our foyer tiled years ago the crew discarded their water into the gardens and it "poisoned" the soil. Plants in these areas either suffered and succumbed within a few years or attempts to replant in the areas eventually failed. So I know fresh concrete isn't good for the fish and I also know it affects the plants in the gardens. Going forward I know there will be natural 'silt' forming but hate to think of starting out on the wrong foot with a murky pond because I never removed the concrete silt before the final water fill.
 
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forgot to welcome you, Welcome :)

I think you just went above my paygrade!! :) certainly outside my experience but not, I would suggest, of the Google.. anything there that supports the poisonous mortar water theory? I've never heard of it.. but I'm not in US so my normal is not your normal... (in so many ways) :)

I see a large difference in a pond made of concrete and some spilt mortar.. also the tiling glue, (also had a large amount of tiling done recently.. ) is usually a specialy formulated mixture not just plain block mortar so you might not be comparing apples with apples??

In any event, welcome to the forum and I would suggest a search of the the massive resource here to cast further light upon the problem.
 
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Thank you for the welcome! :) I tried a search with 3-4 different parameters but no answers with information specific to my problem. I’ll hope someone can help me with my dilemma
 
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Welcome to the GPF!

I don't know if we're talking a few cups of silt or a hundred pounds - it would definitely make a difference. But I'm guessing it's the former and in that case I think you're worrying for no reason, especially in a pond this size. Over time you will get LOTS of silt in the bottom of the pond - its the nature of building something outdoors. Rain brings silt, wind brings silt, organic material breaks down into silt. There's really no avoiding it, unless you filter it out.

I am curious about several things - you said this is an EPDM lined pond. Are you rocking the whole pond? Two reasons I ask - the liner will be very slippery and dogs have sharp claws. I wouldn't allow a dog into an EPDM pond where there is any exposed liner. Just swimming is one thing, but if they panic or struggle to get out, they will very well tear your liner.

One other thing - you say this is a "natural" pond and you have no pump or filter, and yet you lined it and are concerned about silt on the bottom getting stirred up. How do you plan to keep this pond clean? At the size you mentioned, goldfish will do fine without filtration, but I don't know that you'll be happy with the appearance of the pond when it achieves it's "natural" balance.

Just some thoughts!
 
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Welcome to the GPF!


I am curious about several things - you said this is an EPDM lined pond. Are you rocking the whole pond? Two reasons I ask - the liner will be very slippery and dogs have sharp claws. I wouldn't allow a dog into an EPDM pond where there is any exposed liner. Just swimming is one thing, but if they panic or struggle to get out, they will very well tear your liner.

Very good point there, among many, lisak1.

I had a moments panic when I saw it also applies to me... then I remembered I'm putting that "gravel on a roll" on the shallow end!
 
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Thank you Lisa! I’m not at all concerned with the build up of “natural” silt, it’s the concrete silt and the possibility of contaminating the pond for fish or wildlife. The pond will be “filtered” with lots of plants, oxygenating and marginal plantings. The entire liner edge will be rocked (first ledge already completed) and the shallow end will also have flat rocks and river pebbles to protect the liner from the dogs. The foreman has even made steps for the dogs to insure an easy access for my older dog to get in and cool off. Mind you I’m not going to be encouraging them but realize it’s probably inevitable since they love the creek that borders our property! Every detail has been thought out, and rethought, and after months of research I just want to make sure we’re not making a mistake leaving this “unnatural” silt before we do the final fill. The thoughts of filling it, then realizing we made a mistake and need to drain, clean and refill is a major concern. We have to pay for the water to be delivered - $75 for 1800 gal truck. If we have to pay that amount twice it’s going to cost me more than the liner! :(
 

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Hello and welcome! No idea, but I would at least add some air through a fountain. You could hook up a temp. pump and filter to get out the fines. A good water test kit (API Freshwater Master) as well as a KH and GH test will go a long way to assure your water chemistry and conditions will be good.
 
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Stay away from the test strip type test kit, they tend to not be very accurate. Use an api pond test kit or similar kit that has liquid reagents. They are much more accurate.

I'm no concrete or mortar expert, but have been around masons and I've done some of that work before.

The mortar may affect the Ph.

Sometimes a latex additive is mixed with mortar to make it more sticky. I don't know if your guys used that or if it would be harmful to fish or plants. It might be a good idea to ask them.

I'm thinking that any mortar that fell into the water would be diluted, especially with the amount of water you are talking about. But, you didn't mention how much fell in, I guess that would matter.

Also, if you add too much water to a mortar, the sand will tend to separate from the Portland cement. Maybe what you see is suspended sand.

Hopefully the experts will chime in soon.
 
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Lots of good suggestions here. If you really need to set your mind at ease, though, I would simply drain and remove the water you have since it's only 6k gallons at this point. Then don't fill it back up until you've finished construction.

In your case, it sounds like you have just a little bit of cement/mortar in a very large pond, but I do know that concrete formed ponds are typically filled and drained numerous times to leach out excess lime while the concrete cures. It's done over and over until ph is under 8 or so. Doesn't sound like that would really apply to your situation, though.
 
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Again, thank you for the Welcomes! I didn’t realize I forgot to attach a picture. This was taken the day before the mortar was used to secure the floating stones.
7D97CEDF-77ED-49D6-9670-124179D9E798.jpeg
 
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And this was taken 48 hrs after the mortar entered the pond. There is about 1/4” of silt covering everything.

I called the local water garden center where I purchased the liner/underpayment and told her what had happened. Her immediate response was you need to drain and remove, it will not only affect the pH and harm any fish but also any submerged plants, possibly for a long time! With that response I’ll be talking to the contractor at 7 AM and request they drain the pond before any more work is done. Thank you for your suggestions. I’ll come back and post a pic of the finished project!
FAE75A5E-4F5E-49AF-938A-4F7830E2365E.jpeg
 
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if they truly used mortar, it wouldn't hold anyhow as it is not waterproof. Cement/concrete (which is made with cement) is, though. All said, cementing/mortaring stones like that seems pointless and surely won't hold. Exactly how arethe floating stones situated that they needed to be mortared? I'd assume there's a good base upon which they are sitting. Weight should hold them, imo, and should be stable without any bond to worry about. Sounds like there's a bit of engineering if you've got any cantilever effects going on.
That said, you might consider hydraulic cement; it's built for underwater situations.

The mortar will/might affect the pH as mentioned, but it depends on how much was used, as Lisa noted. I doubt a bead of morter would do much in a pond that size but if you're concerned, by all means drain and clean. If they used additives other than pure mortar, then of course the wildlife and flora might be affected adversely.
 
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