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  #1  
Old 03-19-2010, 11:47 AM
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What causes spray paint to "crack" or wrinkle?

This has always been one of those mysteries that annoys the crap out of me.

When applying spray paint...what is it that causes it to "crack" (it doesn't literally crack, but immediately after application it will get lines in it that look like cracks where you can see the original surface), or wrinkle?

I have a set of side covers for my bike that I'm trying to paint and I've been having the absolute worst luck. The first time I painted them, the paint went on too heavy and had bad orange peel. So I sanded them down, painted them again, put the second coat of paint on too soon and the paint wrinkled in several places.

SO, I sanded everything way down a couple weeks ago. Two of the pieces are plastic and one is metal. I stripped the metal piece down to the original paint (factory), and I wetsanded the plastic pieces with 400 grit enough to take out the wrinkled spots and the orange peel.

Last night I wanted to try painting them since it was warm, so I wiped all three down with prep-all and let them dry.

Now this is where it got a tad infuriating for me. I had some filler primer I decided to use to fill the sanding scratches and such.

The first plastic piece I primed got the aforementioned "cracks" in several spots, with the first coat. I thought OK then, maybe I don't want to use the primer...so I got the paint I was gonna use (both were shaken properly) and sprayed the second plastic piece. It almost immediately wrinkled all over the place. ARGH! I was about ready to throw both cans across the street.

At that point I figured well, what the hell, and I primered the third piece, which was the metal one. The primer went on just fine, no cracking or anything weird. WTF.

Shortly after I grabbed the plastic piece that had wrinkled and sanded it down a little (to get rid of the wrinkled spots), wiped it down again with prep all, let it sit for 10 min. or so and sprayed it with primer, and it got cracks in it with the primer just like the first piece did.

I guess these pieces just don't want to be painted...I just don't really understand why they're doing this. Wrong temperature? Something still on the surface? WTF?
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Old 03-19-2010, 12:41 PM
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Wrong paint for plastic. Go to a good paint store and buy spray cans made for plastic. Ask them if you even NEED primer.
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Old 03-21-2010, 11:52 PM
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I have had good results with Krylons Fusion paint for plastics.
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Old 03-22-2010, 01:49 AM
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There are a few reasons why this is happening. One is a reaction of the new paint to the old paint. Another can be contaminates. (Silicon spray is really really bad stuff with paint) Another reason is adhesion. There are adhesion promoters that you spray on first then apply your paint/primer. Another is the wrong type of paint. Also I recommend sanding with 320 grit. I used to use 400, but found that the 320 promoted better adhesion.

My recommendation is to remove all existing paint (use 180 grit) down to bare metal/plastic. Clean surface with a wax and grease remover. On the plastic use the adhesion promotor (Bulldog is one) and prime everything. After it dries, sand with 320 grit and paint.
I have used the Krylon plasic spray with some mixed results, and it sounds like you want a really good finish so I would recommend not using it.
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Old 03-22-2010, 03:51 PM
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I'm trying to paint these pieces with lacquer paint. Problem is I don't really know what primer I'm supposed to use for lacquer.

I sanded the primer down last night and it looks like the filler primer I was using reacted with the old lacquer paint on the two plastic pieces. I think I will try a different primer or something. I've had the worst luck trying to paint these three pieces.
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Old 03-22-2010, 08:43 PM
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Lacquer paints will melt the underlying paints and cause this issue,(It's Hot) switch to an Acrylic and i bet you will not have any problems
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