sealing a car prior to paint

[Larry S.]

Well I am building a 1962 corvette (not excactly "factory correct") any ways the car was paint stripped by chemicals prior to me purchasing the car.I had what every paint that was left on the body media blasted off.

So now the car is ready for a couple of repairs,Stress cracks.And re attaching a replacemennt front left corner of the car,and also a pretty nasty cracked damaged area above the drivers front tire.

So my real question here is what should we use to seal the car? I have done a search of the archive and have not found the information I am looking for.

The reason I feel we need to seal the car is there are way too many areas where the the glass is hairy,wavy,thin,slightly damaged,body seams needing attention.So it would seem like the entire body would have to have almost an entire plastic skim coat on it.Is this what sealer fixes?

I have heard the terms

"slick sand"
"high fill primer"
"gel coat"
"DP"

The car is in a body shop for the repairs and a repaint and I want them to use what is best for the car.

The finish paint is going to be a 2 stage urathane made by ppg called global.

Thank you in advance for your help

Larry

[Ed Jennings]

Re: sealing a car prior to paint

There are a number of products on the market for this purpose, including "gelcoat", which is basically a sprayable resin, and others which contain a filler. My favorite is called "Featherfill". It is a sprayable polyester resin with some sort of fine filler. Featherfill has been on the market since the 70's, so there may be some newer, better products out there. I just used it on a Jeep a few months ago when one of my so-called bodymen tried to strip its fiberglass body with regular paint stripper. It fixed the damaged area on the jeep like new, and the bodyman acquired some new knowledge to take with him to his next job.

[Dick W.]

Re: sealing a car prior to paint

I would use the substrates recommended by PPG for this paint. Usually the local PPG rep is a good resource for the proper materials to use. Ask your painter or paint jobber to put you in touch with him.

[John M.]

Re: sealing a car prior to paint

Larry,
I have used Slick Sand, Feather Fill, DP90, and Gel coat, all four. They all have their uses, and they all have their strength and weaknesss.
Slick Sand and feather fill are basically the same thing. They are both made by the same manufacturer and provide the same performance. They are both polyester resin with an inert filler material. They are high-build surfacers that are intended to fill waves and imperfections in the body when blocking. You can look at them as a sprayable form of body filler, same composition, just thinner.
Gel coat is pure polyester resin that is just sprayed on the bare fiberglass surface to seal down loose strands and consolidate the fine spiderweb cracks that are common on these old cars. DP90 is a self etching epoxy primer. It is a great corrosion resistant primer for steel and a great sealer over old repairs on fiberglass to prevent repair swelling. Now for my opinions of each product and it's uses.....
I think DP90 is a great product, but I have never used it for priming a fiberglass body. I use it for priming all steel parts, and it is tenacious and incredibly tough. It is not a surfacer, and can not be sanded, as you will break through almost imediately. It is a good sealer over old paint and repairs to prevent unwanted reactions between the new paint system and the old paint system. I have never painted a corvette that was not stripped to the bare glass, and have never had to worry about such reactions.
Slick Sand and Feather Fill are good high build primer/surfacers which are polyester in composition and are completely compatiable with fiberglass construction. A lot of peole also use PPG K36, as well as the NCP series of primers. I use NCP271 a lot. The only real advantave of NCP over K36 is that the NCP is a self-etching, corrosion resistant primer surfacer, which is a great choice over steel parts, but this buys you nothing over fiberglass. I prime steel parts regularly, so it is easier to just stock only one primer surfacer. All of these high-build primers are good choices under any urethane topcoats. They all will fill imperfections well and are compatiable with all modern fillers, but they do not , in my opinion, provide the same level of crack suppression as Gelcoat.
Gelcoat is a pure polyester resin with no filler material in it. It is not intended for build up and block sanding. It is intended to seal the surface, and consolidate the tiny spiderweb cracks that are common on a 40 year-old body. If you use gelcoat, you will still need to use one of the high build primer surfacers to level the ipefections by blocking. Being straight polyester resin, the Gelcoat is very hard compared to the other products, and that, in my opinion, is what makes it a superior product for it's intended use. It is, in fact, more brittle, but no more brittle than the base body, since it is the same material. The other products, while polyester in composition, have a large ammount of filler material in them, which allows cracks to telegraph through more easily. The most telling indication, it when a body is stripped. when you strip a gelcoated body, the gelcoat is untouched, but the body with one of the polyester high-build primers surfacers, will allow the stripper to penetrate the primer.
That being said, Gelcoat is not an easy material to work with, and will add many dollars to the finished job if you are paying for the labor. It is a bitch to sand, since it has a parrafin wax that is in suspension in the product, which will form a layer over the gelcaot when sprayed to help its curing. This wax layer must be sanded off with 80 grit paper, and will clog paper almost imediately. The surface of the polyester material itself, has a large ammount of orange peel as well, and must be wet sanded to remove the orange peel and provide a smooth surface. The Slick Sand,and others, also spray out with substantial orange peel as well, but they sand very easily due to their large ammount of inert filler material.
I have absolutely no doubt in my mind that Gel Coat is a superior product to use over a bare body prior to the primer/surfacer, but it is not absolutely necessary, and it will add to the cost if paying for labor. I do all my own work, so the only additional cost to me is the material cost, so it is a good value to me. In your case, vyou will need to weigh the additional cost versus the possible benefits, and make your own decision.

Regards, John McGraw

[Jim T.]

Re: sealing a car prior to paint

John have you ever used gelcoat to spot spray problem areas like around the front corners of the hood area and any other location where only stress cracks may appear after a repaint?

[Larry S.]

Re: sealing a car prior to paint

THANK YOU!
Every one

I now have the information I need and can go foward

[John M.]

Re: sealing a car prior to paint

Jim,
I would never try to repair these stress cracks with gelcoat. When I talk about cracks. I am talking about those hundreds of tiny spiderweb cracks, not the stress cracks you are talking about. The only good solution for these cracks are to grind them out and glass them back in.If they are improperly repaired, nothing will keep them from coming back.

Regards, John McGraw

[David Bodily]

Re: sealing a car prior to paint

John,
I have a 59 that will be one of my retirement projects. The guy I bought the car from had stripped the complete car with regular paint stripper. I thinks he said it was "aircraft" stripper. I know it came in a blue and white gallon can. My question to you is: am I in trouble because he did not use a stipper that was formulated specifically for fiber glass? Thanks for any help David Bodily

[John M.]

Re: sealing a car prior to paint

David,
You are probably OK. All strippers use methelyene chloride as the active agent. some are stronger than others and need to stay on longer. The only real problem with strippers is leaving them on long enough to attack the base glass, or failing to wash/neutralize the stripper after it has done its work. As long as the stripper was completely scrubbed off with soapy water, it should be fine.
When in doubt if any stripper residue is still present, wipe the entire car down with lacquer thinner and then scrub it down with hot, soapy water.

Regards, John McGraw

[Chuck S.]

Re: sealing a car prior to paint

John, I suspect that paint stripper is also becoming more "politically correct".

I bought a quart for a little stripping job, and found that the stuff would hardly touch the 80s vintage black paint on the bumper. It was softening the paint up a little, and I could then use sand paper to take the paint off. No wrinkling and curdling like the old stuff used to do. The acid test: incidental splashes on bare hands didn't burn like the old stufff. I suspect they have cut way back on the methylene chloride, which I believe is a suspected carcinogen.