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Old 11-30-2009, 09:24 AM
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help me understand sprayable body filler

I have seen on youtube where they are block sanding bodies, putting on filler and sanding it off, and then I see people shooting a sprayable polyester after that. I am a novice at this so bear with me. They say that it's the last step before sealing the bodywork. It looks like just the trick to get the last of the small waves, sand marks, and blend the edges of the filler. What are the pro's and cons of this stuff?

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Old 11-30-2009, 11:26 AM
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People generally frown on the use of polyester primer/filler using 2K primer/surfacer instead. The polyester primer/filler is not as durable as 2K primer/surfacer. The use of 2K primer/surfacer in most cases makes the use of a sealer redundant.

Vince
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Old 11-30-2009, 11:52 AM
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What is the difference between the two products that makes the 2K better?
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Old 11-30-2009, 12:14 PM
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Quote:
Originally Posted by xpsyclonex2002
What is the difference between the two products that makes the 2K better?
2K is catalyzed urethane and cures a lot harder than polyester.

Vince
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Old 11-30-2009, 04:22 PM
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Click here for a "Basics of Basics" to all primers that should clear up a lot.

Polyester primer is best left for when you REALLY need some serious filling. Or when what you are doing has many body lines or that sort of thing that would make spreading filler difficult like on a vintage truck tailgate or firewall. In those places it is AWESOME.

But if you don't need serious filling, urethane primer is the way to as Vince said.

Brian
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Old 11-30-2009, 05:39 PM
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poly primer will just shrink and you'll see all the scratches in top coat
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Old 11-30-2009, 06:21 PM
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I have to disagree with you on that. I have tested this stuff, ABUSED it big time with ZERO shrinkage. I have cut filler with nice new sharp 36 grit paper then applied Slick Sand right over that. I blocked it with 180 and 220 and 320 and then 400 and painted over it.

I did this with a spot job on a black car and painted it bc/cc. This car wasn't garaged and I looked at it eight months later and it looked perfect with ZERO shrinkage in the polyester primer. There was some shrinkage in the basecoat as you could see some of the 400 scratches. But the 36 grit scratches filled and not present.

I did this same thing on a Harley gas tank used as a display for five years. It was three stage custom paint and looked like a million bucks.

Nope, shrinking is not a problem. As Vince pointed out, it can be brittle I think, though I have seen super tests on rubber bumpers that would flex without it cracking. But for chips it seems to be a little different and not be as tough.

Brian
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Old 11-30-2009, 09:24 PM
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Martinsr,
that was a darn good link. That helped alot.
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Old 11-30-2009, 10:28 PM
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how does lacquer primer compare to polyester primer?
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Old 11-30-2009, 11:03 PM
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Quote:
Originally Posted by mitmaks
how does lacquer primer compare to polyester primer?
No comparison in any what, other than they are both liquid.

Polyester is THICK, with LOTS of solids, Lacquer is thin with very little solids.

Polyester is a 2K and chemically cures while Lacquer is a 1k and simply "dries" by the evaporation of thinner.

They have nothing in common outside of being liquids BEFORE they are sprayed.

I say "BEFORE" because theoretically dried lacquer primer could be scraped off a fender, put into a can with lacquer thinner and shaken back into a spray-able form! Polyester primer could never do that being it is chemically cured into "another" chemical form.

Brian
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Old 11-30-2009, 11:04 PM
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Quote:
Originally Posted by xpsyclonex2002
Martinsr,
that was a darn good link. That helped alot.
You're very welcome.

Brian
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Old 12-01-2009, 12:16 AM
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Brian, what are you thoughts about painting right over Poly primer? Our boss does it sometimes, and as far as I have been led to believe...its like painting right over body filler, being that they are essentially the same, same resin and same hardner.
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Old 12-01-2009, 07:03 AM
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In addition to what's been pointed out above, I found the polyester sprayable filler to be much more challenging to lay down a nice smooth coat than when using a 2K Urethane primer. I got a lot of orange peel which I couldn't seem to eliminate no matter what my gun settings. So I ended up with most of the poly on the floor after much sanding. But then I'm a very inexperienced painter so I'm sure in the right hands the poly is a good product.

Personally, the next time I shoot primer it will be exclusively 2K Urethane. I'll have to shoot more coats but the results will be much smoother and require a good deal less sanding to get straight.
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Old 12-01-2009, 07:23 AM
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Dewey, if I remember correctly when I used the poly primer I thinned it a little with Acetone to help it spray better.

Vince
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Old 12-01-2009, 07:54 AM
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Yes, you can reduce it with acetone or a quality lacquer thinner. Before the voc rules it was all lacquer thinner, but being acetone is voc exempt all the tech sheets changed from lacquer thinner to acetone. Acetone is a VERY heavy solvent, literally heavy, pick up a gallon of lacquer thinner and a gallon a acetone, BIG difference. So being it is heavy it must be treated with respect or you can trap it.

Dewey, with the right gun and the right reduction depending on the brand it will lay down pretty nice. It will never be consistently as smooth as urethane but it does a different job too.

If you pile on many coats of urethane primer to fill something polyester will do in a coat or two you are going to get into trouble for sure. Polyester primer will literally bury a quarter taped to the panel, it fills THAT much. And is designed to do it.

It is always MUCH better to correct the surface closer so that a few coats of urethane is enough to fill any imperfections to be surfaced out (blocked). But under special circumstances where you really need that big fill of polyester, man-o-man, is it hard to beat.

BMM, again, for some reason (I am not a chemist or privy to the difference) but some polyester primers have recommendations to spray over them, others don't. I think it is mostly the marketing dept that is saying this, but some do and some don't.

Feather Fill G2 is the most user friendly, it is most "urethane like" in characteristics and it has recommendations for top coating. I have only top coated Finish Sand, Slick sand and PLC "Polyprime" all with very good results.

It really isn't the "same" as plastic filler, it is basically, but not the same.

On the same note, I feel much more comfortable using the polyester to FILL then apply a few coats of urethane over it to sand to perfection prior to top coat.

Brian
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