Concrete Pond sealing Advice Please

Posted 7th Aug 2010
My koi pond which is concreted all around was holding water fine for 3-4 years for the last 3 years water drains off to half the pond level and stops there. I tried to look for place where it might be leaking i can't find any cracks or holes, so tried painting with this water seal paint from B&Q.…8l2
But still it's doing the same thing any advice ?
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I would go with a decent pond sealant paint from specialist pond supplier or fish shop. the water seal you have bought is for brickwork and is designed to enhance its life, not make it watertight as with a pond. you need specialist paint which is designed to be in constant contact with pressurised water. once you get below the surface, you encounter water pressure Hence needing the correct paint. it is quite thick stuff and shouldnt take long to dry. Will try and look up something like Blagdon, but a decent shop should be able to advice you more specifically
An alternative, and less eco friendly option if you can not find the source of the leak after all this effort - fit an external tap and run copper pipe to your pond. Fit a cistern ball valve (like in the toilet) either on the top of your filter, or hidden somewhere such as in waterfall pool or even in the main pond behind plants. set it to the water level you require, and as it drops, the valve opens, tops it up and turns off again. This is how I have mine now after replacing my liner twice, including concrete, mesh and waterproofing underneath! The leak is VERY slow. the whole pond level drops around 2 inches in 2-4 weeks depending on weather. and due to the large surface area and vegetation filter, I lose a lot of water to evaporation. So this option solved both issues. Hope this all helps and good luck
Are you sure its the pond leaking not any of the piping or filters,

this is excellent stuff, but costs lots … this is excellent stuff, but costs lots -

I think i will go with this stuff, Mine is only a small pond so i may need only 1.5 litre to 2 litre. I need to find if they do. A very big thankyou to tango42 for all your time and effort in finding the paint and forums.
Edited by: "scorpiostar" 8th Aug 2010

Are you sure its the pond leaking not any of the piping or filters,

Its the pond as i never used the filters this time after i painted.
welcome. I know the trouble this sort of thing causes!
Tell me something guys.

I have 4 Goldfish, all about 3-4 years old, they have been outside in a non filtered pond all their lives and have been in crappy green water, not because I have neglected them, but because I've tried everything apart from a filter and the water stays green all year round.

Went to the fish shop a few times and they suggest everything apart from a filter, and I have no idea about filters etc

I'd love them inside but I don't want to kill them from the change, any advice?

welcome. I know the trouble this sort of thing causes!

Do you think opting for this would be better option than the paint…tml

Do you think opting for this would be better option than the paint … Do you think opting for this would be better option than the paint

this is more for sealing fresh concrete, ie: you have just made a new concrete lined pond, to prevent the chemicals from the concrete from leaking in to the pond water. the gold seal is the way to go in your situation i think Be careful to follow the instructions to the word. let the pond get to the low level you mentioned, and then take some more out so you can apply the paint an extra couple of inches BELOW where the leak has to be (specifically the leak has to be at the level the water falls to but stops )
You can either cover a couple of inches either side of this line, or cover from this point upwards. It depends if you think there is more than one hole. Comes down to cost and time really. I have used this stuff before to sort leaks and it is VERY sticky stuff, so worth getting some decent gloves, not just the washing up ones. something like these would be handy as you really do not want this stuff on your skin -…775 or…486
links don't seem to work. first is - Nitrile Knit Wrist Gloves
Catalogue p170

second is - PVC Gauntlets
Catalogue p170

Pop them in the pages search engine, or look through their catalogue, both page 170. You can probably pick these up from your local pound shop as well MUCH simpler than trying to remove it from your skin I can assure you!!
Thanks a lot tango gr8
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