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How do I waterproof a fibreglass pond?

I moved to a new house and the fishpond had cracks in it. I patched the cracks with a fibreglass repair kit. I’m pretty sure I got all the holes and gaps. I put some water in to test it and it seemed to hold well. But overnight the water level dropped about 50mm. Looking at the pond it seems like water has seeped into the fibreglass which is probably 30 years old. Can I use Crommelin pond sealer to fix this?

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MitchellMc

Welcome to the Bunnings Workshop community @likepizza. It's brilliant to have you join us, and many thanks for your question about sealing a fibreglass pond.

As you've mentioned, it's possible that the water leakage is coming from an area other than the cracks you patched with fibreglass. It's possible that the fibreglass shell itself has become weakened or damaged over time, which could be causing the leakage.

Crommelins pond sealer is designed for cementitious substrates and might not bond suitably to fibreglass. To re-seal a fibreglass shell, you'd use fibreglass resin painted over the entire surface. The best practice would be to sand back any degraded or powdery fibreglass, so the resin has something solid to bite into. Another option is to line the fibreglass shell with a PVC pond liner.

If you did go ahead with the Crommelins pond sealer, please use the coloured products and not the clear. These are two entirely different products, and the coloured variants will be much more suited to your project. Also, ensure the shell is bone dry before applying the membrane, as any residual moisture trapped under the membrane will stop it from curing; if this occurs, the only option is to remove it entirely. Removing the water and allowing the shell to dry out for several weeks would be best.

Please let me know if you have any questions.

Mitchell

likepizza

https://www.workshop.bunnings.com.au/discussion/comment/24505#Comment_24505

Thanks very much for the advice Mitchell, I’ll drain the pond and apply a resin coat throughout as you suggest. Wish I’d asked before I put the water back in!

Jewelleryrescue

Hi @likepizza

I have being badly let down by Crommelins pond sealer mainly as it seams to be a great liner and worked (i was cement and brick work sealing in a lovely pond blue color ) but the product was not UV stable and within 2 years started badly cracking and peeling. It was a night mare to angle grind that back to bare brickwork.

If you use Crommelins make sure it says clearly it is UV stable. If you cant find that written at all then only use indoors.

That shell most likly has Uv Damage and now Osmotic penetration by water which is why its probably leaking now with no obvious holes. Any inlet or outlet pipes below water level they tend to be a source of leaks too.

Tap around the shell look for any soft spots (flaking loose fibres as signs) sand them back as @MitchellMc suggested you will need to use the old fiber glass as a shell for a new fiberglass application over the weak spots or as boat builders use an epoxy gel coat for the remainder all over finish.

I love using cementous water proof paint but it will crack on top of flexable fiberglass. 🙁

As an offering to complement @MitchellMc solutions Consider.

Or there is one other product that is long lasting and flexable but is black and not paintable and that is bitumen paint is Potable once cured and non harmful to fish and plants and has good adhesive properties in extreme sun situations it will fade and may need a new coat of bitumen paint but this is simple to do and probable less expensive than fiber glassing whole pond? and no special preparation apart form loose materials.

This can be also applied to damp surfaces so no fear of drying things 100%

Sika 4L SikaTite BE Bitumen Waterproofer I/N: 0960530 $54

Gripset Betta 1L Waterproofing Membrane Bitumen Rubber I/N: 0960165 $20.56

likepizza

https://www.workshop.bunnings.com.au/discussion/comment/24506#Comment_24506

Thanks for this advice. I looked into Sika Tite but it doesn’t mention fibre glass as a substrate. In any case I think we’d rather keep the existing sandstone colour rather than black if we can so I think we will still do the coat of resin. It’s not really a huge pond so I think maybe a couple litres of resin will cover it.

Thanks also for your good advice about the inlets as well as there is a pump which is hard wired back to a switch and I will double check where the cable is penetrating the pond.

Jude2

https://www.workshop.bunnings.com.au/discussion/comment/24506#Comment_24506

Will the sika be fish friendly?

Jewelleryrescue

https://www.workshop.bunnings.com.au/discussion/comment/75199#Comment_75199

Hi @Jude2

Yes Sika 4L SikaTite BE Bitumen Waterproofer is water potable after 3 water flushes acording to saftey sheet

But I also discovered Sika 4L SikaTite BE Bitumen Waterproofer IS NOT UV STABLE as I First thought so OK indoors or inside planter boxes.

Depending on you pond a cementous paint is fully water proof and UV stable.

EricL

https://www.workshop.bunnings.com.au/discussion/comment/101324#Comment_101324

Hello @Jude2

I suggest going with @Jewelleryrescue's second recommendation which is Gripset Betta 1L Waterproofing Membrane Bitumen Rubber. It is made for use in fishponds and can be used outside.

Eric

Jude2

https://www.workshop.bunnings.com.au/discussion/comment/117592#Comment_117592

Thanks for that EricL.

just to clarify, our problem is that the “pond” (old horse trough) seems to be shedding fibres. You can’t see anything but if I put my hand in the water it is itchy when I take it out. It isn’t leaking, but we want it stable and safe. We will give your suggested product a go

EricL

https://www.workshop.bunnings.com.au/discussion/comment/127039#Comment_127039

Hello @Jude2

Please make sure that the horse trough is bone dry before putting on the Bitumen Rubber. Any trapped moisture inside the surface of the trough will affect the drying process of the membrane and it will not cure properly.

Please keep us updated with your progress, we look forward to seeing the "pond" fully sealed.

Eric

Jude2

https://www.workshop.bunnings.com.au/discussion/comment/133306#Comment_133306

Drained, dried & painted!

Next step will bet th he fish & plants.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/137161#Comment_137161

Lovely work, @Jude2! Many thanks for updating us on your project. The results you've achieved look wonderful.

Please give us another update when you start planting and introducing fish.

Mitchell

Jude2

https://www.workshop.bunnings.com.au/discussion/comment/139822#Comment_139822

Baby fish now in, & happy. Just waiting for the big ones to return from holiday.

EricL

https://www.workshop.bunnings.com.au/discussion/comment/141662#Comment_141662

Hi @Jude2

Thank you very much for posting your fish pond project. It looks fantastic and I'm sure your little fishies will thrive in their new home. What kind of water pump did you use for the pond? Can you also please tell us the plants you've decided to put in?

Again, thank you for sharing such a wonderful project.

Eric

Jude2

https://www.workshop.bunnings.com.au/discussion/comment/141662#Comment_141662

These are the pond plants I used. I also have Liriope, day lily & native violets up to the edge to give insects hidey holes. Big fish are now back & seem very happy😍

Jude2

https://www.workshop.bunnings.com.au/discussion/comment/143045#Comment_143045

Pump was from bunnings. Not sure if the size - that’s the other half’s job. Pond holds about 300litre so he would have gone for a pump with that as mid range capacity. It needed to be stronger to push the water up1 metre to run down the wall

Aquaman

Apparently not it doesn't stick to fibreglass

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/27069#Comment_27069

Hi @Aquaman,

To clarify, fibreglass is not a surface that the supplier has in their recommended list of surfaces for pond sealer as it is flexible and changes dimension when it heats up and cools. The sealer might very well stick to the fibreglass; it's just the supplier can't verify that it won't crack or delaminate at a later stage.

Mitchell

Aquaman

https://www.workshop.bunnings.com.au/discussion/comment/76192#Comment_76192

And there lyes the issue as I'm building a indoor plywood aquarium

Perhaps you advise on this is, is there a No VOC non toxic black sealant that bunnings carry

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/101975#Comment_101975

Not as far as I'm aware @Aquaman. Achieving no VOC for a sealing product would not be easy due to the qualities they need to possess. Even LOW VOC wall paints are a relatively specialised product. Many products stop off-gassing completely when they've cured, but if this is inside, you'd likely need to ventilate the area until that occurs. Could your aquarium be built outside and sealed before it's bought inside?

Mitchell

Aquaman

https://www.workshop.bunnings.com.au/discussion/comment/117972#Comment_117972

Couldn't be worse then fibreglass resin lol

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