Primer, Gel Coat, or Resin???

[Bob B.]

My 1960 body is on the dolly and stripped. There are a few small rough or fuzzy fiberglass spots here and there. I want to paint it, but I'm stuck on what to do to best prep the body. I have PPG DP74LF Primer and DP401LF Catalyst. Some tell me that this is all I need and that it will seal the fibers and provide a good base for the paint. Others say that fibers will eventually show through and that the surface should be gel-coated first, then do the primer. But I hear horror stories about the gel coat setting up so fast that it ruins the paint gun and if you even manage to get it on, it is so hard that you almost can never sand it smooth. Because of the gel coat horrors, others say you should paint it with fiberglass resin, but that doesn't seem much different than gel coating it.

I'm sure if I could ever get gel coat or resin on and sanded flat that the surface would obviously be good, but will just the primer do the same??? Thanks!

(PS: I tried the primer on a couple of test panels. They turned out okay, but a couple of weeks later, I picked up a couple of paint stirrers that were stuck together with the primer, pulled them apart, and the primer between them was still sticky. It seems to me that the catalyst should have hardened it regardless. Is the primer bad, or did I not use enough catalyst, or ???)

[Joe C.]

Re: Primer, Gel Coat, or Resin???

Bob:

As you probably know, there was never a Corvette that was factory surfaced with gelcoat. Polyester gelcoat is basically a polyester based resin, which is very similar to the resin component of your fiberglass composite substrate. The most common gelcoat used is Isothallic, which has excellent water protection characteristics, and is used in marine applications as a color coat over the substrate. For boats it is pigmented, applied, then sanded and polished.
In Corvette application, normally, white or grey gelcoat is applied over the "fiberglass" as a surfacer and moisture barrier. It is very stable, and once catalyzed, it will not shrink/creep, or move in any way.
You should purchase a special spray gun for correct application, preferrably HVLP. You will need to provide an anaerobic (oxygen free) environment for proper cure. This is generally accomplished by application of polyvinly alcohol (PVA) over top coat. There are additives on the market which enable the gelcoat to be sprayed with a comventional spray gun, eliminate the PVA application, and provide excellent flow-out which eliminates much of the final sanding.
I highly recommend the gelcoat underneath an epoxy primer, sealer, color, clearcoat for a flawless finish.
If you prefer to retain the original look of your car, complete with discernable bond seams, then do not gelcoat the body.

Joe

[Ed Jennings]

Re: Primer, Gel Coat, or Resin???

There are sprayable polyester primers such as "FeatherFill" on the market that will probably do what you want. They are much easier to apply and sand than the gelcoats and they will adequately cover the exposed glass fibers. Use a good urethane 2k primer over the entire car after treating the bad spots and you should be good to go.

[Bob B.]

Re: Primer, Gel Coat, or Resin???

Joe,

Thanks for the note! I am using lacquer, which is why I want the best base I can get. What are the additives you mention to make gel-coating much easier, and where can I get them?

Bob

[Dick G.]

Re: Primer, Gel Coat, or Resin???

Bob: I used dp on one panel and covered it with a polyester primer surfacer. DP must be mechanically agitated for at least 5 minutes after mixing. Drill with a mixer works well. I broke through the poly. while blocking and decided to see how well the poly. was adhering to the dp. Not very good. I will never use dp over a bare fiberglass piece again. RTFL: Read The F Label. Well, today we don't get enough info on Body product container labels so always insist on a P-sheet(product sheet).I used Featherfill on my car and loved it. Stay away from Slick Sand. Even thinned down and sprayed with a garden hose it left a textured surface. First: are you in a rush to paint this car? If so wipe it down and spry wet with featherfill and start blocking but your results will show through surely. If no rush read on: After Washing body let dry, clean the car's surface with an alcohol wipe down product PPG I think it is dx133?? You should buy Ecklers fiberglass repair book but skip the gel coat process. Not neccessary for a show quality job. Reglass all seams and remove ALL old bondo, glass all cracks in glass. Make sure all attaching trim, doors, etc. fit before you repair in its area. OK when your done with getting it as straight as you can with a Minimum of bondo, block once the entire with 80 to 120 grit dry preparing it for its first application of poly. Always wipe it down to rid the body of oils. Where PPA face and hands. Follow the p-sheets directions to the letter. No guessing. 3 wet coats poly.. Guidecoat primer. Blocksand wet with a long board. A paint stick works great wrapped with sandpaper. Apply more poly again. Save yourself headaches and go to autobodystore.com It is a forum of bodymen from around the country that will help you. Read and research will reward you and minimize your mistakes. Sorry this post is so jaded. Too much info. for a post. http://bis.midco.net/gutmans

[Joe C.]

Re: Primer, Gel Coat, or Resin???

http://www.duratec1.com/dp07.html

[Chuck S.]

I Have Seen The Light...

And the "Light" in Corvette painting is...GELCOAT. I had already made up my mind!...I wasn't going to use it!...And now I have seen the light!

You shudda' gone to the NCRS National Convention in Park City; there was an excellent paint seminar by Ken Schow, a professional that has been painting Corvettes for about 25 years. He recommends always using gelcoat to seal the fiberglass...said that gelcoat serves as an impenetrable barrier against anything coming out of the fiberglass to cause the paint to blister (cleaning/bodywork solvents, oils, grease). He said that epoxy primers, fiberfill, featherfill, et al are NOT imprevious to solvents and oils, and if you have those demons in your fiberglass, you will get blistering eventually.

When you saw the panels he had on display demonstrating the stages in the painting process, you understood why he doesn't mind using gelcoat: The gelcoat section had absolutely no moonscape texture...it was as smooth as a baby's bottom. It was only going to take a little sanding with 80 grit, then 180 grit to get it ready to top coat. I didn't get to talk to him to find out how he sprays it with virtually no orange peel, but I suspect it involves working with a pressurized pot, spraying the entire car quickly using a large nozzle, and cleaning up ASAP. If you think gelcoat sets up fast in the gun, you really wouldn't like spraying urethane primer-surfacer...pot life is 30 minutes; you have to mix it one 20 ounce cup at a time.

Gelcoat is essentially polyester resin, but no catalyst is added...air must be kept from getting to the material surface for it to cure properly. There are two types of gelcoat...one type has a sealing agent mixed in the gelcoat, and the sealer migrates to the surface after the material is sprayed...the other type gelcoat has to be sprayed with sealer (PVA or polyvinyl alcohol?) immediately after it is applied. The first type is what Schow and most use on Corvettes; the second type is primarily used on boats. I plan to find out more about spraying technique and sources when the time comes.

That's not to say that you can't paint a Corvette without gelcoat and get a great paint job...happens all the time. It is also true that no Corvette was ever gelcoated at the factory...but the difference is they were painting brand-new, virgin fiberglass with no exposure to gasoline, oils, grease, and solvents. If your car has had any oil/grease leaks onto body panels (e.g. leaking AC compressor seal, leaking brake MC, etc.), gelcoat is pretty much a necessity if you don't want blistering.

As for your primer not setting up, you definitely have a problem. Catalyzed materials will set up solid to at least an inch in thickness if left in the open container. My opinion is your catalyst has gone south. Once opened, catalyst has about a six month shelf life. You may be able to push that a little, but the risk of wasting much more in labor and materials is not worth it...After six months I buy new and pitch the old. It's expensive, but that's the nature of the "catalyzed" beast...You need to learn to plan your painting well and work as efficiently as possible.

[John M.]

Re: I Have Seen The Light...

The thing that made up my mind for me years ago was when stripping second generation paint jobs. Cars painted with slicksand or featherfill, when stripped with chemical stripper, the stripper will remove the Slicksand. Stripper will not remove the Gelcoat! There is too much inert material in polyester primer/surfacers and this will allow stripper to penetrate just like a sponge. It will also allow things to come out from under, and will allow thinners to penetrate and swell old repairs.I have painted cars with both methods, and both will provide nice results, but I believe that you just can not beat the sealing and spiderweb crack consolidation that is provided by a solid resin gelcoat as opposed to a primer that has a high inert material content. This material is meant to provide high build and easy sanding, but I believe that it does not do that good a job of sealing over repairs and spiderweb cracks. I use a high build primer surfacer, but I use it on top of the gelcoat, not in lieu of it! There is no doubt that gelcoat is a pain to apply and even a worse pain to sand, but it is worth it to me. I might have a different opinion if I paid for may paint jobs, since It does add a substantial cost to a finished job, but as long as I do my own work, the additional cost is fairly minimal, just a lot of extra hours!

Regards, John McGraw

[Scott stuckly]

Re: I Have Seen The Light...

Kudos on gelcoat!!

I just went through this same issue myself contiplating the recommendations on using epoxy primers or polyester primers and decided to go with gelcoat over my bare fiberglass on my C1. I had to make many repairs on my glass and felt that the gelcoat was the way to go to seal up the body that sat bare in my garage for 5 + years.

I used a new product from Evercoat called One-Step Finish Gelcoat. http://www.evercoat.com/newproducts.aspx It uses an MEK hardner and cures without the need of a release agent or sealing agent mixed into the gelcoat. It cost a bit more than original gelcoat but when it dries there is no wax build up that has to be removed like some other gelcoats.

I used a 2.2mm HVLP spray gun and thinned the gelcoat with 10% acetone as recommended on the label for spraying.

Regards,

Scott

[Dick G.]

Re: I Have Seen The Light...

It is simply a choice. None of the big boys like PPG, Dupont make gel-coat. I wouldn't be sold simply because of one seminar from one man's opinion on gel-coat. Now go to autobodystore.com and ask professional bodymen from around the country about gel-coat. If you are worried that something is going to rise up from underneath than do a thorough cleaning with acetone on top and on the bottom of the panels. Research research research. Thanks and have fun.

[Ray C.]

Re: I Have Seen The Light...

Hi!

John M., is there a particular brand of gel coat that you would recommend? I am in the process of prepping a 1963 SWC for paint. I will be using PPG lacquer and my PPG supplier recommended that I call PPG service-technical department to get advise on how to prepare a Corvette for lacquer. The PPG representative advised me to gel coat. I should have asked them if there was a recommended brand, but I didn't.

Thanks Ray

[Richard S.]

Re: I Have Seen The Light...

I attended the paint seminar in Park City. I will soon be repainting my 67 due to paint problems. We used Gelcoat to prep the body before painting. At the seminar I learned that the car should receive TWO coats of Gelcoat....not one coat. I now believe my 67's problems stem from the fact that we only used one coat of Gelcoat and that it was mostly sanded off in some places during prep. Hope this helps prevent someone else from having to repaint a car......

[Steven S.]

Re: Primer, Gel Coat, or Resin???

Lots of conversation about gel coat, but a lot of mis- info as well. #1 gel coat is a polyster resin product with fillers and pigments added. #2 it is used to make boats, shower stalls and such. It is put in the mold first then resin and glass is put in behind it to create the part. The part is pulled from the mold and the gel coat is a hard glossy surface with no rubbing or poishing needed. If the mold is dull the part will be dull. The gel coat takes on the same luster as the mold. #3 The gel coat can be applied as a paint coating, but needs to be 20 mils (20 thousands of an inch) thick wet to cure properly. Catalyst is used - MEKP. Gel coat sets up in 15 to 30 minutes, so must be out of the spray gun that fast. It is thick and usually sprays with a lumpy orange peeled surface. Can be hard to sand. There are additives that can be added that help the surface to dry tack free for easy sanding and helping it to spray better. These are normally only available to large users like manufacturers. Gel coat can be applied to 2 coats, but no with surfacing additives in it. The additive is wax and will cause adhesion problems with 2nd coat. Gel coat needs to be applied properly and with the proper catalsyt levels. Too little catalyst and it will not cure properly, too much and the same thing will happen. Needs to be between 1.2% and 3% catalyst depending on the temp. you are applying it in. Higher temp, less catalsyt. Using a pot gun with EX tips and needles (large hole) or pressure feed gun with FX tip and needle. #4 there are only a hand full of manufacturers of gel coats in the US: Valspar, HK Research, Ashland Chemical, Cook Composites, Interplastics, Alpha Owens Corning are the main ones. All these companies only make it in 5 gallon pails or larger.

Steve