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Another question for the frp pros
ChrisLeary - 23/8/13 at 03:43 PM

Afternoon all,

I've taken the mould of a scuttle, but the gel coat seems to have reacted with the halfords paint I used on the plug leaving a very poor surface finish. The resin used was polyester, is it common that it will react with certain paints?

So, for future reference, what should I be using for the final coat on the plug? I don't have the equipment to spray, so something I can brush coat would be good. I read somewhere that upol reface can be applied by brush and that it would be good for a final coat.

Any advice please?

Thanks,

Chris

Carbonman - 23/8/13 at 04:50 PM

quote:
Originally posted by ChrisLeary
Afternoon all,

I've taken the mould of a scuttle, but the gel coat seems to have reacted with the halfords paint I used on the plug leaving a very poor surface finish. The resin used was polyester, is it common that it will react with certain paints?

So, for future reference, what should I be using for the final coat on the plug? I don't have the equipment to spray, so something I can brush coat would be good. I read somewhere that upol reface can be applied by brush and that it would be good for a final coat.

Any advice please?

Thanks,

Chris


When you say" reacted" did the paint come off with the mould when you separated them? As a general rule both Poly and Epoxy Resins will react with" rattle can" paints, its the Styrene content. Having said that you can also get wrinkles in the gelcoat for other reasons, gelcoat applied to thickly or the backing layers applied too soon.

ChrisLeary - 23/8/13 at 06:18 PM

Thank you for the reply.

I think it reacted because the paint looked like snow flakes on the surface of the plug when seperated. Also there seemed to be paint left on the inside of the mould.

This is my first attempt at grp, so it could be down to the gel being too thick, and it not being left long enough, I was so concerned I'd leave it too long, so that probably has something to do with it.

How long should I leave it before laying the first laminate? And is there anything else I can do to ensure a good finish on the mould?

Thanks again,
Chris

Carbonman - 23/8/13 at 06:41 PM

Ok sounds like a few issues going on at once.
You can get away with rattle can paint as long as its not "green" ie has been left for several weeks/months to cure, by that time most of the styrene should have gone. Not usually a luxury we have in the real world. Another option is to use a 2K paint but that has H&S issues for the home worker. Even then it has to be cured remember once the exotherm kicks in the mould will reach temperatures of 60 plus degrees, softening the "plug" coating.
You can apply a good thick coat of PVA to create a barrier between the plug and the gelcoat, but you will have plenty of work to do on the mould surface to get a decent finish. If its a fairly simple plug you can cover the surface with either parcel tape or cling film, poly or epoxy won't stick/react with those but again plenty of finishing to do on the mould.
The best thing you can do is to "befriend" your local bodyshop and get them to 2K and bake it for you.
As for the gelcoat timings. Gelcoat wont fully cure without the the laminating resin being applied on top. As a rule of thumb minimum 3 hours and a maximum of 24 hours before lay-up, but will vary depending on ambient temps. The gelcoat should feel tacky but not come off on your glove when touched. Hope that helps. Warren

ChrisLeary - 23/8/13 at 07:19 PM

quote:
Originally posted by Carbonman
Ok sounds like a few issues going on at once.
You can get away with rattle can paint as long as its not "green" ie has been left for several weeks/months to cure, by that time most of the styrene should have gone. Not usually a luxury we have in the real world. Another option is to use a 2K paint but that has H&S issues for the home worker. Even then it has to be cured remember once the exotherm kicks in the mould will reach temperatures of 60 plus degrees, softening the "plug" coating.
You can apply a good thick coat of PVA to create a barrier between the plug and the gelcoat, but you will have plenty of work to do on the mould surface to get a decent finish. If its a fairly simple plug you can cover the surface with either parcel tape or cling film, poly or epoxy won't stick/react with those but again plenty of finishing to do on the mould.
The best thing you can do is to "befriend" your local bodyshop and get them to 2K and bake it for you.
As for the gelcoat timings. Gelcoat wont fully cure without the the laminating resin being applied on top. As a rule of thumb minimum 3 hours and a maximum of 24 hours before lay-up, but will vary depending on ambient temps. The gelcoat should feel tacky but not come off on your glove when touched. Hope that helps. Warren


Warren, thank you so much for the informative reply. That really is some great advice for a future project I have.

Thank you again,

Chris

Carbonman - 23/8/13 at 07:23 PM

No problem, you could always attend one of my courses and learn all the "trade secrets" Lol