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Old 01-19-2009, 08:57 PM
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Plastic Bumper Question

I have limited painting experience. My Jeep still looks good, but you would never call it a show vehicle. Now I am working my wife's Miata, with a plastic bumper to add to the complexity.

I have seen a variety of recommendations on painting plastic bumpers. Some involve quite detailed preparation and others use Dawn/Scotch Pads and go. Many give conflicting advice. Here is what I am thinking is best, from what I can tell. Please comment on what I could do better:

1. Sand those areas (lower edges) to eliminate dings, nicks, etc. This typically takes the plastic bumper down to black plastic. Generally this is along the undersides of the bumper.

2. Clean and buff the remainder of the bumper using liquid detergent and a Scotch Pad or fine sand paper and blend in the newly sanded plastic with the buffed areas. In other words, don't take the whole bumper/grill to black plastic, just the parts that need it.

3. Shoot plastic primer covering the whole assembly to get a uniform surface for the base coats. Wet sand, as necessary, to get a smooth yet buffed surface for the paint on the whole assembly.

4. Shoot base coat layers, wet sand as necessary, and establish a good color coating. Wet sand or rub out the orange peel before applying the clear coat.

5. Shoot clear coat, with flex agent, to cover and protect the paint coat. Apply two coats to allow for buffing.

6. Buff out any imperfections in the clear coat using progressively finer rubbing compounds.

Where should I use the plastic adhesion product, if at all. There is a lot of conflicting advice on that. Thanks.

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Old 01-20-2009, 09:39 AM
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Here is the basics, you only need adhesion promotor on the bare plastic. You only need "Plastic primer" on the bare plastic. And you don't need to prime the whole thing if it has good paint on it. The painted area, you treat just as you would metal with paint on it, scuff it and shoot over it.

Just remember, unless you are going to build a bunch of primer up and make it brittle, there is no need to thread the paint any different, the paint you are applying on it doesn't "know" there is plastic under it.

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Old 01-20-2009, 11:35 AM
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Comprehension Check

If I understand correctly, then I ought to prime the portion that was sanded down to bare plastic (i.e. to get the scratches out) with plastic primer. So:

1. I buff up the currently painted areas to permit a good grip by the new paint. No need to take it down to plastic.

2. Apply the plastic primer to the bare plastic part (feather the primer over te previously painted area) in order to ensure full coverage of the plastic by either primer or old paint. Lightly sand, as required to ensure there is no "line" visible.

3. Shoot base coat normally.

4. Shoot the clear coat with flex agent.
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Old 01-20-2009, 12:33 PM
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It sounds like you got the basics. Here's a tip,, If the scratches are deep you can use a small skim of body filler to fill them instead of sanding them out. Bodyfiller doesn't shrink as much as heavy coats of primer which can cause "bullseyes" in the finish. Remember to use a little coarser grit of sandpaper before applying the filler, better adhesion . Another tip, If most of the bumper is decent, cover the primered spots first, then give the bumpera couple of coats overall. To help with colormatch you may want to use one thousand grit paper on theareas where the bumper fits against the fenders. Usually 8 inches is far enough to lightly blend up to the original color on the fenders. then when the clearcoat is sprayed over the whole bumper there will be only clear next to original finish, thus giving the illusion that the bumper hasn't been damaged.
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Old 01-20-2009, 02:25 PM
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I was thinking about doing the primed area first and "building it up" to be primed and color coated before shooting a couple of layers on the whole thing. That way, it has a good color match with the final coats. Thanks for the ideas.
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