![]() Factors such as grit shape, bonding material and grit durability can all influence effective fineness. No need for filler on small door dings.We have chosen to use effective (or actual) micron grit size as the scale by which we can compare the effective fineness of stones, understanding that particle size alone is not the only determinant of finish. You should check out the paint on Dodge trucks, the e-coat is so thick you can shape body panels with it. If your still that concerned about it, only do two coats, or even one, and spend forever carefully sanding it out trying not to burn though. ![]() Were talking about a bare plastic bumper. But were talking like at least 3 paintjobs before it starts to become a problem. Too much product on a surface does make it fragile. Three coats is recommended, two and you don't have enough material to work with, and four you run the risk of shrinkage. You can spray on as much paint on as you want. What you are saying is not making sense, don't use the proper high build primer becuase its too thick, yet spray 15 coats of rattle can paint to build up the surface enough to be able to work with, which is the equivalent of 3 coats of high build. It is guaranteed to be lesser quality that the two part high build. Meaning that it has no hardener, catalyst, activator, etc. Paint sprayed from an aerosol can is a one part mix. Plastic was never designed to be painted. That said, the 20 year old paint on the front bumper of my rs is spider cracked from one end to the other. 3 coats of high build with a flex agent and an adhesion premoter should withstand just as much abuse as the original paint. Spray high build primer on a piece of plastic and bend it after it dries, you'll see why.I do, everyday. That is basically it in a nutshell, fell free to ask questions or express opinions. Once the bumper is finished in 600 its ready for base/clear. Block sanding isn't really necessary here because there arn't any large flat surfaces. You should really use a HVLP gun and a high build primer, although rattle cans would probably work but it would be rough, and the amount that you would need wouldn't be much better cost wise.Īfter you've primed and guide coated, sand with 400 on a D/A or 600 by hand until the guide coat is gone. A primer with a flex agent in it is required to prevent the paint from cracking when the bumper flexes. ![]() If you spray primer over the fuzzy surface you will see the plastic sticking up through the paint, and flooding the primer on to cover over will cause problems. Sanding the urethane with 180 will make the surface somewhat hairy, you need to sand all the fuzzys out with either 320 or 400 grit, until the surface is smooth. This will probably require stripping the whole bumper. Chances are the paint on the bumper is cracked everywhere, you need to sand all the cracks out, or they will show through the new paint. Any coarser grit is really overkill and you end up with plastic fuzzies on the surface, which you dont want. If your just worried about cracked paint and not shape then I would strip the paint down with 180 grit. I bought a nice 3M one for work a few years ago for about $180 canadian, but you could probably get a lower quality one for under a hundred. It would be a great investment if you ever plan on doing body work again. Trying to strip the paint off one of these bumpers by hand isn't very realistic, if you own an air compressor then your best bet would be to purchase a dual action air sander.
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