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I’m venturing into the world of body work. Total novice here but I have a quart of Eastwood polyester primer. It says it adheres excellent to fiber glass. I want to use it on my new lt1 hood that I’m putting on. Would this primer be suitable and do the job correctly?
From: At my Bar drinking and wrenching in Lafayette Colorado
As additional info, here is what I use when doing a body job:
After stripping the car down to bare metal/substrate (or as far down as it needs to go), I seal it with a coat of epoxy. This acts as a corrosion/oxidation inhibitor and as an adhesion promoter for all subsequent body work/fillers. I do all my body work/glass work/filler work on top of the epoxy coated car and get it as smooth as possible. I then shoot the entire car with a heavy coat of polyester (the stuff you have on hand). This is like spraying the entire car with body filler. I block this down using a guidecoat to assure that I have nailed the panel straightness/smoothness. Over the top of this blocked-down polyester coat, I then shoot a couple of coats of 2K urethane fill-primer. I guidecoat it and block it down. If my previous bodywork and blocking job on the polyester was good, this final blocking job is finished with 600 grit in prep for final paint. If the guidecoat reveals low spots, I repeat the 2K fill primer process and finish off with 600. This final blocking and 600 wet-sand prep will usually result in some "cut-through" down to the polyester or the substrate at the high spots or on edges. Once the car is in the paint booth, and after a detailed prep and wipe-down, I then shoot a thin coat of epoxy, reduced as a sealer, on the entire vehicle to assure no problem spots in the cut-through areas: If you have any of the polyester primer exposed in a cut-through area, you will have nothing but pinholes in your final paint in that area. Once the entire car has been sealed, and the epoxy sealer has dried (you can also use 2K urethane as a sealer by reducing it down), "nub" it to remove any imperfections and paint it. The epoxy or 2K sealer can usually be "nubbed," wiped down, and topcoated within an hour.
So in answer to your initial question, the polyester primer you have is usable, but only for one step of the priming process. A quart isn't going to get you very far: It might do a single panel, such as your hood.
Lars
From: At my Bar drinking and wrenching in Lafayette Colorado
You can use polyester primer as a fill primer for block sanding and smoothing the surface (polyester primer is like "Bond-O" in thin, sprayable form). You cannot paint over the top of a polyester primer- you have to seal it with either a 2K urethane or an epoxy primer/sealer before applying paint.
You can use polyester primer as a fill primer for block sanding and smoothing the surface (polyester primer is like "Bond-O" in thin, sprayable form). You cannot paint over the top of a polyester primer- you have to seal it with either a 2K urethane or an epoxy primer/sealer before applying paint.
thank you for that. What is the difference between the epoxy primer and the urethane?
From: At my Bar drinking and wrenching in Lafayette Colorado
The urethane 2K primers are sandable fill-primers that can be reduced and used as a sealer, and also used as a fill-primer for doing final block-sanding and surface smoothing. The epoxy primers are not sandable, and cannot be used as a fill-primer. They are used as sealers, adhesion promoters, and surface prep/corrosion inhibitors, or when sealing & isolating underlaying finishes & products from the topcoats. From the PPG recommendations:
"Epoxy Primer is an excellent corrosion-resistant primer and provides excellent adhesion to many types of properly prepared metal, fiberglass and aluminum substrates, as well as plastic fillers (i.e., polyester). Epoxy Primer may also be used as a sealer and topcoated with most refinish products."
Lars
From: At my Bar drinking and wrenching in Lafayette Colorado
As additional info, here is what I use when doing a body job:
After stripping the car down to bare metal/substrate (or as far down as it needs to go), I seal it with a coat of epoxy. This acts as a corrosion/oxidation inhibitor and as an adhesion promoter for all subsequent body work/fillers. I do all my body work/glass work/filler work on top of the epoxy coated car and get it as smooth as possible. I then shoot the entire car with a heavy coat of polyester (the stuff you have on hand). This is like spraying the entire car with body filler. I block this down using a guidecoat to assure that I have nailed the panel straightness/smoothness. Over the top of this blocked-down polyester coat, I then shoot a couple of coats of 2K urethane fill-primer. I guidecoat it and block it down. If my previous bodywork and blocking job on the polyester was good, this final blocking job is finished with 600 grit in prep for final paint. If the guidecoat reveals low spots, I repeat the 2K fill primer process and finish off with 600. This final blocking and 600 wet-sand prep will usually result in some "cut-through" down to the polyester or the substrate at the high spots or on edges. Once the car is in the paint booth, and after a detailed prep and wipe-down, I then shoot a thin coat of epoxy, reduced as a sealer, on the entire vehicle to assure no problem spots in the cut-through areas: If you have any of the polyester primer exposed in a cut-through area, you will have nothing but pinholes in your final paint in that area. Once the entire car has been sealed, and the epoxy sealer has dried (you can also use 2K urethane as a sealer by reducing it down), "nub" it to remove any imperfections and paint it. The epoxy or 2K sealer can usually be "nubbed," wiped down, and topcoated within an hour.
So in answer to your initial question, the polyester primer you have is usable, but only for one step of the priming process. A quart isn't going to get you very far: It might do a single panel, such as your hood.
Lars
This is great information. Thank you so much. I did the underside of the hood to gain experience. Used the whole quart. Then body worked again. Then sprayed Probase primer-sealer. Then 2 basecoats, then 2 clear coats. Not bad for never having done body work before.
Just before spraying primer. My home made set up for a paint booth. It did the trick. After primer. Wiper cowl after primer. First base coat Second coat Setting up the “booth”
From: At my Bar drinking and wrenching in Lafayette Colorado
Very nice job. Excellent. It makes you realize just how much work it is to do nice body & paint, doesn't it..? Imagine doing that amount of work to the entire car, noting how much materials you used and the time it took, and paying yourself a reasonable shop rate of $120/hour, and you understand why nobody good is doing Corvette paint jobs for $5,000.... I'm guessing you have over 10 hours in the underside of that hood, plus materials, which means you would have had to charge around $1500 to make it worth your while to do that work for somebody else. And that's just the bottom of the hood...
Lars
Very nice job. Excellent. It makes you realize just how much work it is to do nice body & paint, doesn't it..? Imaging doing that amount of work to the entire car, noting how much materials you used and the time it took, and paying yourself a reasonable shop rate of $120/hour, and you understand why nobody good is doing Corvette paint jobs for $5,000.... I'm guessing you have over 10 hours in the underside of that hood, plus materials, which means you would have had to charge around $1500 to make it worth your while to do that work for somebody else. And that's just the bottom of the hood...
Lars
You just about nailed it. At least 10 hours of labor. Probably more due to being a novice. But yes, totally see why guys are charging so much. I had a guy quote $1200 to do both sides of the hood. Makes more sense to me why now.
From: At my Bar drinking and wrenching in Lafayette Colorado
Yes. That's what you want to use. But first use the "gel coat" as a sanding base - the gel coat is very much like a polyester, so use it as a blocking fill primer. You have a long file-board that you're using, right..? Shoot a guide coat on the hood and block it down with the file board in a cross-hatch pattern: you'll be surprised how "wavy" it is. Put a couple of coats of urethane fill-primer on it after blocking (not reduced as a sealer), guide-coat it, and block it down again starting with 150 and going to 220. Repeat as necessary to get a clean sand on the guide coat with 220, and finish sand 600 wet with guide coat. If you have not cut through the urethane in any area, you can basecoat/clearcoat over the top. If you have any concern that you may have a cut-through to gel-coat or 'glass substrate, shoot an epoxy seal coat or a urethane primer coat reduced as a sealer prior to the first basecoat. You're on the right track to doing it right - nice job.
'67 hood shot in polyester (similar to your gelcoat) prior to initial block-down:
Hood can here be seen after block-down of polyester with urethane fill-primer and guide-coat applied - prior to final blocking of the urethane fill-primer:
Urethane fill primer with guidecoat blocked out and finished 600 wet, with the "cut-through" areas identified and sealed with epoxy:
Yes. That's what you want to use. But first use the "gel coat" as a sanding base - the gel coat is very much like a polyester, so use it as a blocking fill primer. You have a long file-board that you're using, right..? Shoot a guide coat on the hood and block it down with the file board in a cross-hatch pattern: you'll be surprised how "wavy" it is. Put a couple of coats of urethane fill-primer on it after blocking (not reduced as a sealer), guide-coat it, and block it down again starting with 150 and going to 220. Repeat as necessary to get a clean sand on the guide coat with 220, and finish sand 600 wet with guide coat. If you have not cut through the urethane in any area, you can basecoat/clearcoat over the top. If you have any concern that you may have a cut-through to gel-coat or 'glass substrate, shoot an epoxy seal coat or a urethane primer coat reduced as a sealer prior to the first basecoat. You're on the right track to doing it right - nice job.
'67 hood shot in polyester (similar to your gelcoat) prior to initial block-down:
Hood can here be seen after block-down of polyester with urethane fill-primer and guide-coat applied - prior to final blocking of the urethane fill-primer:
Urethane fill primer with guidecoat blocked out and finished 600 wet, with the "cut-through" areas identified and sealed with epoxy:
Shot and finished:
Lars
those are outstanding looking results.
so even though the hood is brand new and the gel coat finish looks very straight I should still block sand?
Last edited by Bluesting70; Nov 22, 2022 at 09:58 AM.
From: At my Bar drinking and wrenching in Lafayette Colorado
There is not a new, out-of-the-mold fiberglass panel that is straight and wave-free. Hit it a few times in a cross-hatch pattern with your long file board and you'll be shocked to see the high spots and waves. If you shoot a nice glossy paint job on it without blocking it, it will look like a 10-year-old did your bodywork...
There is not a new, out-of-the-mold fiberglass panel that is straight and wave-free. Hit it a few times in a cross-hatch pattern with your long file board and you'll be shocked to see the high spots and waves. If you shoot a nice glossy paint job on it without blocking it, it will look like a 10-year-old did your bodywork...
glad you responded. I would have not thought that. Than you
My ‘69 is in primer, but I have no idea what kind it is. To be safe, and per the advice from @lars, my plan is to first shoot it with some epoxy, do body work and block it down, then shoot with Polyester, block it down, then 2k urethane before I shoot my single-stage.
I’ve got a spare t-top that I am going to do a trial run on first to make sure I know what I am doing, then similar to @bluesting70 I have a gel coat L88 long hood to block and paint as well. Then maybe I will feel confident enough to move on to the whole car.
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