Gel coat onto plywood.

[driver0606]

Hello,
I want to coat some plywood with gel coat to match part of a GRP boat. Does the plywood need something between it and the gel coat or can the latter be applied directly?
As always, all suggestions gratefully received.
John.

 

[BERT T]

Coat the ply with Bondaglass G4 first. http://www.cfsnet.co.uk/acatalog/G4_DampSeal_Brochure.pdf

 

[Avocet]

I think you can, but a quick coat of laminating resin first, will soak further into the ply and act as a good tie coat. Depending on how big / exposed the surface is, I'd be a bit worried about the gelcoat cracking as the wood expands or shrinks though. Might be better putting a few layers of glass tissue over the wood first and then the gelcoat on top of that.

 

[Norman_E]

You need Flowcoat, not Gelcoat. The difference is that Flowcoat or Topcoat as it is also called have wax added. The wax floats to the surface and excludes air so that the polyester sets properly. If you just paint gelcoat onto a surface it does not set properly because of contact with the oxygen in the air. You can just add wax to ordinary gelcoat, but its not easy to mix and it is probably better to buy ready mixed flowcoat.
There is a better explanation here http://www.cfsnet.co.uk/acatalog/methods_flowcoating.html

 

[driver0606]

Thanks guys, great advice, as usual on this forum.
John.

 

[Avocet]

You need Flowcoat, not Gelcoat. The difference is that Flowcoat or Topcoat as it is also called have wax added. The wax floats to the surface and excludes air so that the polyester sets properly. If you just paint gelcoat onto a surface it does not set properly because of contact with the oxygen in the air. You can just add wax to ordinary gelcoat, but its not easy to mix and it is probably better to buy ready mixed flowcoat.
There is a better explanation here http://www.cfsnet.co.uk/acatalog/methods_flowcoating.html

Good point! Yes, I forgot that! If the OP has already bought gelcoat, you can buy wax in styrene solution and that's very easy to ad to the gelcoat. Just add it in the same way as you add the catalyst. These days I prefer to just buy gelcoat rather than having to keep both, and I just add the wax when I want to turn some into flowcoat.

 

[jon711]

You will find that the wood will suck the catalyst out of the flow/gel coat causing a layer of uncured flow/gel coat. An old boatbuilders trick to reduce this was to paint the wood in accelerator (and let that soak in) first..

Jon

 

[PCUK]

Deeply score the ply to give good adhesion and then apply a coat of mat and resin prior to the waxed gelcoat.