Thread: Need advice priming a fiberglass body

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I'm planning on beginning the priming process on my T bucket body this weekend, and need advice on what the sequence of primers should be.

I've painted some fiberglass boats, and we would scuff the hull gelcoat, degrease it, and then use a product like Interlux Multithane Primer, that was semi thin and acted to "etch" the hull so paint would stick. But I am not sure what automotive type primers I should buy to do the T.

Most of the body is well sanded gelcoat, and some places are cut through to the mat underneath. I want to use a surfacing primer that I can lay up in several coats so I can block sand most of it back off, but do I need some kind of primer first to get this surfacing primer to adhere?

I could ask at the paint store, but I figured with all the guys on here who have painted a glass car, I would get much better advice.

Thanks in advance guys.

Don

no i just used the two parts paints like ppg primers the k2s or k36 i sanded up to 220 and wax and grease remover like ppg 330. before you prime to get any hand and skin oils off the body before you prime . YOU MUST HAVE A GOOD MASK i have been very sick from two part paint used them every day and in time it will get you

Pat, are those considered surfacing primers so I can lay it on pretty heavy and block sand it down? The reason I ask is, the etch primer I used for bare metal wasn't really a good sanding one. You could lay other primers on top of it to do that. You know what I am trying to accomplish, get some kind of primer on there that is sort of soft and sands down easily and fills well.

Don

I've done dozens of Vettes, kit cars, and street rods. As long as you use a two part primer, the job will turn out pretty well.

My advise is to add a couple extra coats, then guide coat and block with 360 or 400 before paint. If you find wobbles or flaws, use a two-part glaze, like Fiberglass Evercoat's"Euroglaze". Reblock them, and reprime or seal those spots before paint.

Air dried primers can lead to all sorts of shinkage problems after the paint is finished. I've tried 'em all, so don't even go that way!

BTW, no reason for a self etching primer, if it's not on metal. The purpose for the etch is to neutralize rust or corrosion, which doesn't happen with 'glass.

yes just use the two part primers no sealer is needed first .i used this stuff on alot of substrates.... try to do all your body work with filler not that putty ... even a two part with some thinner in it can make that putty swim around when you hit it with more primer so all ways cut it and open it up so it can get the thinners out of the primers

Thanks Pat and HRP, really appreciate the info. I just assumed I would need some "first" primer to bite into the gelcoat. Ok, that makes my life easier. I'll head to the paint store tomorrow.

Thanks again guys.

Don

i would use epoxy on it. it is all i use on vettes and does a great job sealing it. seal the inside too as fiberglass never stops curing .

Originally Posted by shine

i would use epoxy on it. it is all i use on vettes and does a great job sealing it. seal the inside too as fiberglass never stops curing .

I have been using epoxy primer (thanks Shine) on what few 'glass parts(front fenders) are on my car then using a 2K primer as a surfacer for final block sanding. Epoxy acts as an agent to help adhere the BC/CC to the surface and will also act as a bit of cushion against road rash. When I did the underside of the fenders I got some over spray on the topside that needed to be leveled before I epoxied - fantastic adhesion .

If this is a TP body, it might also help against gel coat stress cracks as well (from personal experience)

No, it's a Speedway body, but probably prone to the same stress cracks. That is why I have laid up so much more glass into it, as it was semi-thin originally, as are most $ 500 bodies.

Thanks for all the advice guys, and let me ask something else. I'm confused by all the terms for primers and paints. What are the differences between epoxy primer, two part primer, high build primer, etc. The epoxy primer I used on my frame was a 1 to 1 mix. The high build I used was something like 4-2-1 mix. What exactly is 2 part, 1 to 1?

Also, I want a primer that has high build characteristics so I can block sand the heck out of it and get it pretty straight. Is this two part you guys suggest high build? The epoxy I used seemed to not have that property, and did not sand well.

So many products and terms.


Don

Two part generally refers to the basic paint plus a catalyst, the thinner doesn't count in that terminology. The numbers you used, such as 4-2-1 are mixing ratios for basic, catalyst, and thinner respectively.

Alternate terms to what's used in this discussion are primer, and primer-surfacer (The "high" build, sandable material).

In simplified terms (you can read the tech sheets for more thorough description), a primer is something to prepare the surface for the top coats. So, as an example, an epoxy primer is used on bare metal or glass to give a ground coat for adhesion (think of a foundation if using a house building reference), and they are used as sealers when painting over other material, e.g. body filler, previous paint, so on.

Primer-surfacers are what are usually called 2k (in todays terminology), or 'high build". Basically they also provide a "ground coat", or the foundation analogy again, but have a high solids content that builds a thicker film than the "straight" primers so that you can block sand for a smoother finish. They don't contain an epoxy per se, so some folks like to have the added "grip" of an epoxy primer under the high build primer.

One last thing I'd emphasize based on the way things have been said here just for clarity sake; ALWAYS clean a glass body with wax and grease remover BEFORE ever touching it with a piece of abrasive paper, much less any paint or filler.

Originally Posted by Itoldyouso

So many products and terms.


Don

Don,
I use Southern Polyurethane (SPI) epoxy. It is fairly easy to apply, 1 to 1 ratio reasonably priced and can actually be used for the final prime coat with graduated sanding - 220, 320/400, 600 and has a 7 day recoat. Others like DuPont/Nason are good as well but do not have the build characteristics and cannot be sanded and only have a 24 hour recoat.

SPI epoxy is not available everywhere but can be mail ordered from Baker PBE: http://www.bakerpbe.com/. Go to 'the other forum' and you will be able to do a search on this stuff. If you have any questions - give me a PM as Brent might get a bit touchy, but you can also talk to the owner of SPI if you call there and he will give you straight stuff

Just to add another comment on why some would do the epoxy primer first, then the primer-surfacer, the epoxy primer will do a strong mechanical bond to a properly prepared surface (generally speaking, roughened with a lower numbered abrasive). Then the bond between the primer and the primer-surfacer is a chemical bond if applied within the specified (on the product tech sheet) time frame.

Originally Posted by Bob Parmenter

Just to add another comment on why some would do the epoxy primer first, then the primer-surfacer, the epoxy primer will do a strong mechanical bond to a properly prepared surface (generally speaking, roughened with a lower numbered abrasive). Then the bond between the primer and the primer-surfacer is a chemical bond if applied within the specified (on the product tech sheet) time frame.

60 to 100 grit works - these are all epoxied with SPI

Thanks Bob and Dave, that info helps a lot. I sort of felt I needed something to bite into the gelcoat, and yet I also wanted a high build primer to get rid of any low spots and allow me to DA and block sand until it is much smoother.

I may move up from the Nason line I have been using on the frame and running gear.

Don

BTW Bob, I bought some pantyhose last night, and have to admit they really do pull the slivvers out. I could see the white stuff on them after using them, and I had no itch last night. Thanks. I was on the fence between regular and control top.............................

Don