Old concrete pond sealing (Australia)

[Bensl]

Hi all.

I have just discovered this forum after searching for solutions to seal an old concrete pond.

Concrete is quite rough and the previous builders have embedded a number of rocks throughout. It also has a couple of trees close to the edge who’s roots are probably not helping things.

I am trying to decide between a liner and some sort of flexible pond sealer but unsure what to use.

Pond measures roughly 6x6m and approx 900mm at the deepest point.

Any advice or help on what to use would be greatly appreciated.

Many thanks.

 

[j.w]

@Bensl

 

[JRS]

Welcome to the forum. I would think a quality liner with an underlayment would be your best bet for the long term.

 

[addy1]

Welcome to the forum!

I would use a liner and underlayment

 

[GBBUDD]

Welcome mate,
The first challenge will be getting the concrete clean. More than likely your going to need a 4 to 5000 psi pressure washer to get it to the point that you could get a coating to stick properly. a 2000 psi just to see what you have to work with. if the concrete is solid . loose, pealing, alagatoring , or cracks.

but if the design has rocks in the water in the middle of the concrete underwater unless the concrete goes under those rocks and not just up to them is one of the hardest seals to make.

IF the concrete looks ok with the dirt on it it may be worth thinking about repair if it look rogh before you clean it a liner would be advisable but the rocks along the edge would have to go or go over them

 

[zeuspaul]

Another option is Rapid Set Mortar Mix. Unknown if it is available in Australia. Lowes and Home Depot stock it here in the USA.

Rapid Set is similar to portland cement in its application. It is stronger than portland cement and does not shrink.

I applied it with a trowel about 1 cm thick to a 34000 liter 3 meter deep reservoir constructed of concrete block. That was about eight years ago and it is still holding water.

If you use a flexible seal it may be difficult to service it later. With the mortar mix you can clean and apply more later if necessary.

If the pond is not structurally sound a liner would probably be better.

 

[Bensl]

Welcome to the forum. I would think a quality liner with an underlayment would be your best bet for the long term.

Thanks. That’s what I was leaning towards after more research. This is what I was looking at. Would it be ok? Not cheap!

AquaTough EPDM Pond Liner - Love My Pond

Aqua Tough EPDM Rubber Pond Liner is a versatile, fish friendly solution for lining your pond, dam or other water feature.This roll measures 6m by 9.1m

lovemypond.com.au

What sort of underlay? I was thinking of using old carpet maybe or should I use the proper stuff?
Cheers.

 

[Bensl]

the rocks along the edge would have to go or go over them

Hi mate. Thanks for the reply. Can you please explain why the rocks would need to go if I used a liner? I thought I could just run it up the edge. It wouldn’t really matter if water got behind it would it?

cheers

 

[Bensl]

Another option is Rapid Set Mortar Mix.

Cheers. I’m sure we would have something similar here. My worry is that if the concrete under has cracked, this stuff would crack eventually too.

 

[zeuspaul]

Cheers. I’m sure we would have something similar here. My worry is that if the concrete under has cracked, this stuff would crack eventually too.

If they are structural cracks it will most likely crack again. If they are shrinkage cracks likely not.

 

[GBBUDD]

Hi mate. Thanks for the reply. Can you please explain why the rocks would need to go if I used a liner? I thought I could just run it up the edge. It wouldn’t really matter if water got behind it would it?

cheers

It won't matter if it gets behind the liner? if your concrete pond leaks then yes it does matter whats the point in a liner.

 

[GBBUDD]

why the rocks would need to go

They could stay but when you only bring the liner to the curb rocks the liner will always be visible.

 

[Bensl]

whats the point in a liner.

I mean if a “little” water gets behind.

 

[GBBUDD]

If you concrete ends up holding water and only leaks as it comes up to the rocks then my suggestion would be to remove the rocks and re set them in new mortar.

because letting water get under the liner can be dissasterous if it builds . it can create whats known as a hippo. thats where the water below has know where to go and it lifts the liner

 

[JRS]

What sort of underlay? I was thinking of using old carpet maybe or should I use the proper stuff?

Some have used carpet, just make sure you any staples or anything else sharp is removed. I used non woven geotextile underlayment from the local home improvement store which is made of polypropylene like purpose made pond underlayment.

Thanks. That’s what I was leaning towards after more research. This is what I was looking at. Would it be ok? Not cheap!

Yes, that is considered the gold standard for garden ponds. Equivalent to what we measure as 45mil EPDM here.