GRP

[lexi]

Evening all.
I am laying up a mould just now . In these lowish temps is it ok to apply the gelcoat and leave till morning and then apply lay up resin and matt.

Alex

 

[ShipsWoofy]

No, unless you are in a heated shed.

Minimum 15°C is not a pretend figure, last time I did some matting in winter I ended up have to remove it all (still mostly soggy) a week later.

I did it again, but left a heater on over night and it worked fine and dandy.

plus, you want the gel coat to be tacky when you start applying mat and resin, if it is not going off or takes so long that you miss the tacky part you could end up with some pretty serious blisters very quickly.

Just my tuppence.

 

[Avocet]

Depending on what the mould is for, how intricate it is, how many times you're going to use it and whether you want to keep it (etc)...

...I wouldn't be too bothered. I've been laying up bits and pieces in the garage recently and have had no trouble. I did put about 3% catalyst in though. The gelcoat should be tacky in the morning. If it is still too runny, apply some gentle heat until it goes tacky. Same with the laminate above it.

 

[boatmike]

Unless you have heating it is far too cold to layup anything using conventional resins. Assuming you have heating to 16degrees C there is no problem doing Gel-coat and leaving overnight. Unless you have wax in your Gel-coat (which you shouldnt have) it will stay surface tacky for a long time. Usually up to 72 hours is permissable but you should get at least one coat of CSM down ASAP.

 

[lexi]

Thanks for every reply. It was a mould for a rear wheelarch on a Seven type car. I only need two lifts from it. On samples I don`t think the gel coat was tacky enough.
The garage has a fire and temps are reasonable. I was thinking that even next day the gel would still be green enough to chemically bond with lay up and matt. It never seems to go completely off in this weather. I applied gel last night at about 5pm in garage and layed it up about 3hrs later.
Left heater on overnight. It seems solid enough. Layed up a rib /spine into it today with a bit of rope protruding each end to help me pull it out. This addition is going off OK. Will it be ok to pull it out of mould tomorrow. It is only 1squ. metre. Anyone doing this for a living I take my hat off to them.
Alex

 

[Avocet]

If you've got it well supported with plywood stiffeners, you MIGHT be OK but to be honest, I'd be inclined to wait until it is reasonably dry to the touch and then take it into the house (if you can get away with it!) and leave it for a day or so. The wheelarch is a fairly big, floppy expanse of fibreglass and there is a good chance that it will continue to change shape as it cures more fully. This can happen weeks after the initial layup in cold weather. Leaving the gel overnight in this weather before adding laminate won't be a problem at all. It doesn't have to actually stick to your finger to make a good bond with the laminate, the tiniest bit of tackiness is sufficient and it should stay like that (in this weather) for several days. I used to work for a company that made GRP sports cars and they regularly used to leave moulds gelled over a weekend and then put the laminate on first thing Monday morning. They did, however, bake the mouldings in an oven for up to 8 hours at temperatures up to 80 centigrade before trying to prime and paint them so as to prevent subsequent movement. This manifested itself as "rippling" under the paint. Lots of GRP cars look great when they leave the showroom but give them a year in the sun, then hold a strip light near them and look at the reflection of the strip light. It's often very wavy!

 

[lexi]

Thanks Avocet. I did get away with taking it inside for a bit but then the wife came home early and asked "what the heck is that" as I was wrapping it in Christmas paper /forums/images/graemlins/ooo.gif
It all turned out pretty good except for one problem.
Inside the mould which is an Mdf, Hardboard affair. There is a radius of polyfilla in one of the 90deg angles. This gives the rear gaurd a nice bullnose. Despite smoothing it and filling it reapeatedly, then allowing to cure and applying 5 coats of Simonize wax, the the contoured radius still sicks to the lifted layup. It`s as though there is a reaction when the gelcoat hits the polyfilla and it cuts the wax and all sticks. The gel brushes onto it ok and covers it. Every thing is as clean as a whistle on the waxed hardboard and mdf.
Alex

 

[Avocet]

Try using plasticine instead to make the radius!

Failing that, try car body filler. I guess the polyfilla is very brittle and might not stick to the MDF that well. Don't know how it would react to Simonize wax either!

 

[lexi]

Thanks. Too much Plasticene needed I fear but I will keep it in mind for future. The Polyfilla sticks quite well to the Mdf. It is the Polyfilla that is sticking to the finished product in large areas. When you gently remove it the gel underneath comes off as well soft and gooey Some West system as a filler and a paint will be needed I think. The polyfilla may be porous with suction. Body filla it is.
Alex