Gel Coat Question

[Mark A.]

I Will Be Gel-coating The Body On My 71 After Stripping All The Paint Off. My Question Is, What Grit Paper Should Be Used To Get The Gc Ready For Primer? And Should I Sand The Gc Like A Primer Surfacer And Try To Level The Surface, Or Should I Just Sand It For Adhesion, And Level It Off With The Primer Surfacer? Thanks, Mark

[Rick E.]

Re: Gel Coat Question

Mark, I gelcoated my car and sanded it with 80 grit sandpaper. I did use sanding blocks when sanding it. After the gelcoat i used high build primer and block sanded it until i was happy. Its alot of work but very rewarding when it is finished. I was told to use 80 grit to have good tooth for the primer to adhere. Good luck

[Mark A.]

Re: Gel Coat Question

Rick,
That sounds good. Thanks for the reply. Mark

[Mike G.]

Re: Gel Coat Question

80-120 grit sounds fine to me. But, since the gelcoat is your barrier layer, I wouldn't try to level the surface with aggressive blocking. You don't want to expose the underlying substrate.

A safer approach would be to guide coat the gelcoat and lightly block it to highlight any major low areas. Those areas would get body filler.

At that point, 2K high-build primer/surfacer would be used to get the surface fully trued up and ready for sealer & top coating.

Hopefully W.W. will offer his expert opinion, to which I will obviously defer!

[Mark A.]

Re: Gel Coat Question

I was told that all filler work should be done before putting on the gel-coat? Then on top of the GC would go primer surfacer and sealer. Mark

[Steve L.]

Re: Gel Coat Question

There are people on this forum and others that swear they would not use gel coat??

[Mark A.]

Re: Gel Coat Question

I found out first hand the awful things that happen when GC is not used. I totally stripped and repainted my 69. I used urethane primers on the bare glass, refinishing it as you would a steel body. After a few months, you could see every place where a repair had been made. The primers soak into the glass and shrink the repair. I'll never make that mistake again. Mark

[Rich P.]

Re: Gel Coat Question

Mark,

It is actually heat that cures the repairs and shrinks them. (That is if you use the right materials) So what you need to do is "cook" the repairs and get them hotter than they ever will be in the sun and they won't move. I use a heat light to accomplish this.

Rich

[Richard R.]

Re: Gel Coat Question

Mark, what shape is your body after the paint removal process? If your body does not have deep gouges or dings I would just use epoxy primer like DP40 lead free. I have gel-coated 2 c-3's and a Donzi speed boat and it is a pain. For one thing a normal spray gun does not work very well. It takes a larger orfice than for paint. I bought one for the last one I did, it really helps. If you do gel coat, after it sets up wipe it down with denatured alcahol to remove the wax that floats to the top after applying. I used to use acetone but it attacks the GC. It takes at least 80 grit to sand the GC after it sets. Call me if I can help. Later Reed

[Dick W.]

Re: Gel Coat Question

I found out first hand the awful things that happen when GC is not used. I totally stripped and repainted my 69. I used urethane primers on the bare glass, refinishing it as you would a steel body. After a few months, you could see every place where a repair had been made. The primers soak into the glass and shrink the repair. I'll never make that mistake again. Mark

That is the reason you use a primer (preferably an epoxy), a polyester primer surfacer, and then seal the primer with an epoxy sealer immediately before painting. I always liked to sit a body outside for a month or so before the final sanding. I looked at a car that we painted in 1985 or 1986. The car had extensive body work before we painted it. We primed the bare glass with PPG DP, used PPG K-36 primer, rolled it outside for about six weeks, did the final sanding, sealed it with DP reduced 100% and immediately painted it with Deltron. NO evidence of any body work showing. The body had the normal waves and seam shrinkage.

[Russ S.]

Re: Gel Coat Question

All pre 1973 vettes should be gel coated over bare glass not over fillers. I put down three to four coats and then spray a coat of poly vinyl alcohol as the last coat because GC is suppose to cure in the absence of air. I then block sand with 120 grit heavily. I then lay down three more coats of GC-again useing PVA as the sealer(this needs to be washed off with water before sanding)I then block sand with 180 grit and prime with 2k primer. I have finished cars that had body damage with out using a speck of filler with this process because the GC has a high fill capability. The reason I do as many coats of GC and sand considerable of it off is because GC is far cheaper than useing the primer as your filler and sanding it off. A spray gun with a 2.2 orifice works very well. One word of caution. Do not use too much activator especially on a hot day and don't wait more than a few minutes between coats as the gel coat can flash off too long(cure) and the next coat won't stick to the previous coat. You are then sanding most of it off ad starting over. For those who are wondering, the reason I state pre 73 is because to my knowledge there isn't a GC designed for SMC glass.

[Jim D.]

Re: Gel Coat Question

There are people on this forum and others that swear they would not use gel coat??

I'm one of them. Never had a problem with any of the cars I've painted. GM never used a gel coat. I see no need to either.

[Dick W.]

Re: Gel Coat Question

I gel coated two, my first and last. After all the work it took to prepare the car for paint, I swore I would never do another. We painted quite a few Vettes using the procedure I outlined in an earlier post and never had any problems

[Timothy B.]

Re: Gel Coat Question

I agree with Dick,

The DP epoxy primer than a sandable primer with lots of sun and six weeks between any coats. Last, DP mixed as a sealer just before paint and it lays down flat as a board and one hour later top coat.

When restoring my 63 frame I used DP epoxy primer and I refinshed a few parts a second time, that stuff is harder to remove than rust..

[Dick W.]

Re: Gel Coat Question

I agree with Dick,

The DP epoxy primer than a sandable primer with lots of sun and six weeks between any coats. Last, DP mixed as a sealer just before paint and it lays down flat as a board and one hour later top coat.

When restoring my 63 frame I used DP epoxy primer and I refinshed a few parts a second time, that stuff is harder to remove than rust..

Tim, DP is not designed to be sanded, it is just a primer and has no filling properties. The only time it is recommended to sand DP is if it has been over 7 days since you sprayed it and have not put another substrate on it. Normally it depends on chemical bonding, not mechanical (sanding) for adhesion. K-36 is a good primer-surfacer and can be sanded.