Thread: Polyester Primer

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I'm using Sherwin Williams 21 Polyester primer-surfacer on my fiberglass '34. Since this type of primer is a 1st cousin to the fiberglass resin, it's the right one to use . . . but, it's driving me crazy. I simply cannot get it to lay reasonbly flat. There's a slight orange peel to it that's really agravating. It's not hard to sand off, but I just shouldn't have to.

I'm using a DeVilbiss HVLP with a 1.8 tip. 23 psi in should give me about 10 psi at the cap, and I have a regulator right in front of the gun. I have a 7hp, 60 gallon compressor with all the filters, so I have plenty of good air. I've used this gun to lay down urthane primers, basecoats and clear coats - no problem. I used it to put the urethane primer on my '34 frame - no problem. However, I just can't make it work with this two-part catylized primer.

I'm not really looking for suggestions on how to spray this smoother, since I'm pretty well done with the last coat, and I've tried just about everything in the book (more air, less air, more distance, less distance, more fluid, less fluid, etc.) However, I'd like to know whether this type of primer is more difficult to spray than regular urethane primers.

. . . or maybe, I've just lost it.

Jack: HOTRODPAINT and some others will be able to give you some really great answers, I'm sure, but maybe it is related to temperature. It is now June, and you are in Virginia, so maybe a slower catalyst or less might be the answer?

I donno, just a thought.


Don

Don,

The catalyist is the same that's used in fiberglass resin - the clear liquid that comes in a little tube. There's only 0.75 oz per quart, so it would be pretty hard to adjust. The instructions say to use acetone (up to 10%) to increase flow-out and pot life. I don't think there's a problem with the drying time, because it takes about 50 minutes to dry to the touch.

Somehow, I'm just not getting it properly atomized coming out of the gun. Maybe the gun is just not adjustable enough. I'll just sand the orange peel out of it. I'm certainly not going to try to use my BB/CC gun to try to spray more primer.

I used to use a similar product, though I can't remember the name off hand. It was a catalyzed gray polyester resin product. It didn't lay down well either, but I block ALL my primer, and it sanded very easily, so I guide coated and got busy.

Most of the new high solids/low VOC primers and paints lay on with quite a bit of orange peeling. You could probably thin a lot more than 10%, but clean air laws limit manufactureres to the amount of volatile hydrocarbons in the paint, that is why they list such low numbers. Before thinning more, though, I suggest you try a less volatile thinner such as MEK. MEK will give the primer a little more time to level out before it starts to set. Check with the manufacturer for compatibility.

For future reference, you can lay down any epoxy primer on fiberglass. After that, use whichever paint system you want. The epoxy primer will act as a barrier which prevents chemicals that may cause fiberglass to deteriorate from coming in contact with the fiberglass.

Thanks, guys. I was starting to think I didn't know how to run a primer gun anymore.

I've already blocked the gelcoat with 80, primed and blocked with 120, primed and blocked with 320, now I'll just hit it again with 400, then 600 and get ready to make it yellow.

The only problem with this is that all of the raised body moldings on a '34 are a PITA to get at and sand smooth without cutting grooves in either the body or the molding.

I have used polyester primers before but on steel. Realy had no problems but we did sand the entire body several times. The paint was Glasarot I think thats the spelling its made in Germany. That is the most forgiving paint I ever used but you have to go by the book step by step.

After thinking about it a bit, I'm betting that the 10% thinner limit has nothing to do with getting the best flow out. They set that limit to keep the Feds happy about the amount of VOCs given off.

I don't have a problem with the final finish - just the amount of extra work it takes to get there . . . although, I should be used to the extra work - it's a Gibbon body . . .

Originally Posted by Henry Rifle

. . . although, I should be used to the extra work - it's a Gibbon body . . .

Jack, maybe if ya give Kyle a call he will come help do some blocking????????

I think the polyester resin product I used was "Featherfill". I remember it going on "bumpy".

My assumption that the Sherwin-Williams' 10% thinner limit had more to do with VOCs than with making the paint lay down was apparently correct. I just reshot my doors with the primer thinned 20%, and all the orange peel went away.

You're a lawbreaker now.

Yeah, but the primer looks good . . .

Originally Posted by 76GMC1500

You're a lawbreaker now.

First time that ever happened, huh Jack?????

Amendment V

No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a grand jury, except in cases arising in the land or naval forces, or in the militia, when in actual service in time of war or public danger; nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation.