8 replies to this topic

[exodusofficer]

I have a large concrete pond, 10 years old. It's developed a lot of small cracks over the years, each year we patch it and it's just leaking again in a few months. Any advice on long term crack repairs? Or should I go with a paint on sealant like Pond Shield? Do those really work, and how long do they last?

[DrDave]

Go to a concrete supply and purchase a 30# bag of Thoroseal. Mix it into toothpase consistancey and it will seal any crack up to 1/2".
I used it on my big waterfall 3 years ago and it is still holding today.

[exodusofficer]

Thank you! Is it necessary to widen the smaller cracks or chisel them out, or should I just use a putty knife and get it into the crack as best as I can?

[DrDave]

The realy small cracks can be sealed by thinning the product until it seeps into the crack. I would not chip away unless you want to make that a trough to hold the thin stuff, then come back with a thicker coat to cover your chiseled out area. I used sand and small rocks in my larger cracks. that allowed me to hide the thoroseal which is a light grey material.

I used a paint brush to apply mine in some areas and putty knife in others, You can also put it into a bag and cut the corner then squeeze it out deep into large cracks.

I had boulders that were too heavy to move but had settled over the years away from each other. My leaks were so massive, the 5200 GPH pump had trouble keeping up with the leaks. This stuff fixed all the gaps and cracks.

It is not cheap. Be prepared to pay about $50 for a #30 lb bag. I don't think you can get any other size.

If you want to prep the surface first, very carefully use muriatic acid (pool acid) to clean the cracks. Muricatic acid is Hydrchloric acid in a weak solution. In small amounts, I wouldn't even worry about nuetralizing it. It will eventually loose its potency especially when the water flows.

[undrtkr_00]

Be careful with the muriatic acid if you get some. I got a couple gallons from our local Home Depot and that stuff is potent! I was using it for adjusting water pH in a big aquarium, but I have only used a couple of cups in more than a year. Maybe you have access to a weaker solution, but you definitely need gloves and safety glasses with the stuff I got.

In terms of how it will affect your water pH, it will likely be offset by the fact that you are going to have some cement curing in your water - the acid and cement will work against each other.

[exodusofficer]

Will this stuff cure if the concrete remains wet? When we drain out the ponds, water from the surrounding soil seeps in just enough to keep the cracks moist.

[DrDave]

Muriatic acid is 33-40% by volume. You only need a very small amount in the crack itself for cleaning.

As for the damp cracks, the thoroseal should be heavy enough to stop any seepage in the first application. A 2nd, thicker coat will finish it off.

The cement will nuetralize the acid by virtue of its reaction with it. Just be very stingy if you choose to use it and wear protective clothing and a facemask.

[exodusofficer]

Can I use this stuff to coat the whole pond or can you recommend a paint to use? All the patches are starting to look pretty bad.

[DrDave]

You can acid wash it, but then you will have to rinse and nuetralize the acid very well. This is how they acid wash pools that have stains and calcium deposits. It will leave the surface finish like coarse sandpaper because it opens the surface up. The concrete disolves and leaves the sand and rocks exposed.