How do I waterproof a fibreglass pond?

[likepizza]

  

 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?

[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]

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]

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]

Will the sika be fish friendly?

[Jewelleryrescue]

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]

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]

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]

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