Paint repair of roughly 3"x3" on a fiberglass bumper - Hot Rod Forum : Hotrodders Bulletin Board -- Hot Rod Forum

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Old 01-11-2008, 10:28 AM
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Paint repair of roughly 3"x3" on a fiberglass bumper

Hey folks-

I haven't done a whole lot of paint work, and its been a while since i've done body work. I have a newer car that grazed a snow bank and lost a little paint (down to the primer it looks like) right around the fog light. What I envision doing is sanding the area down so that I remove all the bits of paint in a defined shape down to the same level with sandpaper. Then probably rough up the primer so that I can mask and spray a new coat of primer down, sand and prep that and re-mask, then go with a pre-mixed paint and mask, spray and wetsand.

Any suggestions or am I way off here?


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Old 01-11-2008, 04:04 PM
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Is this a urethane bumper? I am going to assume this is a urethane bumper that is clearcoated.
This is how you would do it using automotive paint (no spray bomb stuff) for a good repair.

I would sand the area, until any scratches or flaking paint are out and feather out the edge of the paint (maybe around 220 grit range) around the repair area and then sand out around the area you feathered with the grit thats recommend for the basecoat you are using (600ish for most base metallics). Feel the feathered spot with your hand and fingers held flat, that you can't easily feel where your sanding ended, and there is a gradual transition from the sanded area into the existing paint.

If a urethane bumer, adhesion promoter is not really needed if you do end up going down far enough that you get into the bare urethane. Many plastics do require an adhesion promoter anywhere you break through to plastic. Using one before primer if you go down to the raw material, on urethane or plastic would not hurt anyway. If you can stay so you don't break through to primer, you don't need to worry about using an adhesion promotor.

You can use a 2k finishing putty or glaze if you have any deeper scratches to fill at all. Its fine to use the finishing type puttys over epoxy or sanded urethane, primer or paint as well. If you are down to raw material, an epoxy primer may be best first. In fact you could use only epoxy primer on the area if you don't need much fill, and then wetsand the spot for paint, (many epoxys don't sand real well dry).

Make sure the bumper is clean and wiped with wax and grease remover before you even start sanding on it, so you don't sand any contaminates into the paint or plastic, and also wipe down with some kind of paint prep or wax and grease remover before paint and give it good time to evaporate before painting, then you can tack rag off lightly just prior to shooting paint.

Sand your final primer area with somewhere around 600 wet, the rest of the bumper with 800-1000 grit wet range, trying not to break though the clear (any spots you break through clear to base will need to be rebased) and spray your primer spot or any other spots that need color, and blend it further out into the existing color once you have coverage, and then after some good sit time, clear the whole bumper (its possible to blend, but clearing the whole thing will be the best chance at a good looking lasting repair, and its likely the smallest amount of clear you will be able to purchase is a quart, which will give you plenty for the bumper anyways). Many paint suppliers on the other hand will mix up smaller quantitys of base, usually as little as half pint. Be a little carefull with your first coat of clear, as with only a 800 scratch, it can slide a bit easy if you lay on a bit too heavy. Usually 2-3 coats of clear is sufficient, 3 will give you more room if wetsanding and buffing after.

You can sand and buff after painting (waiting till clear has cured enough time) to remove any flaws or dirtnibs if its needed. Read the tech sheets for your products and they will tell you grit range, flash times, and how to mix and activate
I take it you really only ended up with a spot of missing paint on this that basically needs feathering, a shot of epoxy primer on the spot and painting, but if its dented in, with urethane and some plastics, you usually can work out any dents or deformation by heating the area with a heat gun, and working out with your hands (wearing gloves of course), they often have a good memory and wants to go back where it was. Good example. Kid brought a set of urethane skirts awhile back, and test fitting them they didn't fit right. May have possibly been the way they were shipped. A little time spent heating them in front of a kerosene heater and they fit as they should.
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Old 01-11-2008, 04:12 PM
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Arghh, this will teach me for not totally reading the title. FIberglass, basically same type of repair as far as feathering, priming and painting. If you end up with any Bare fiberglass at all it really needs an epoxy primer down on it, and adhesion promotor is not needed. Fiberglass can change shape with heat, but it does not move easily. Look for stress cracks, and if you have them and there in the glass get down into the fiberglass a ways with courser grit and fill with a little bit of finishing filler and sand it off before priming. If its really smc, then its best to use products that say its for use on smc.
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