Paint Flacking Off

Hi, I recently bought a aerosol spray paint from an auto body supply retailer to match the color of my mazda 3. I used it mainly to repair the damage done to my back bumper where i had a whole through it just under the license plate. I fixed that and so far so good it has nearly been a month. However a couple of weeks ago I tried to use the paint to touch up my front bumper as there a few stone chips under the fog light. It seemed to have gone well until I went on a drive to Toronto from Sudbury last weekend. Between the rain and driving on the 400 i had paint flaking off in a few different places. Any ideas why this would happen a week after i did the touch up?

How did you prep the surface before you painted it, and did you use primer?

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Originally Posted by Donutz

How did you prep the surface before you painted it, and did you use primer?

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And did you sand the surface first? At least remove all wax and etc.?

I washed down the entire panel before I begun my procedure. I sanded down the area where the stone chips were with 150, 500, 1000 and 2000 grit sand paper. The surrounding area I cleaned with soap and water as well as a little windex.

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Originally Posted by italian_stallion

The surrounding area I cleaned with soap and water as well as a little windex.

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There's part of the the problem right there. Soap leaves a residue. The correct thing to do once you are done sanding is wipe the area with alcohol or mineral spirits to remove any dust & grease. Once the surface is dry you can apply primer. Use very thin coats. And on bumpers you will get the best results if your primer and paint have a flex agent.

Yeah I never used the primer...partly because I was told that painting overtop of paint of the same color didn't require primer, right now I i tried cleaning the surface with paint thinner (to break down the wax) and then cleaned the area with dish soap and water , sanded, washed again and then rinsed using a pressure washer and dried the area and use commercial window cleaner that contains alcohol. Is there any chance that may work or should I wait a couple days sand it down and try again?

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Originally Posted by italian_stallion

Yeah I never used the primer...partly because I was told that painting overtop of paint of the same color didn't require primer, right now I i tried cleaning the surface with paint thinner (to break down the wax) and then cleaned the area with dish soap and water , sanded, washed again and then rinsed using a pressure washer and dried the area and use commercial window cleaner that contains alcohol. Is there any chance that may work or should I wait a couple days sand it down and try again?

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You should be good to go. Once it is dry hit it with a couple of coats of primer, but don't let the first coat dry too long. Once the primer is setup you can give it light sanding and then a couple coats of paint, with a light sanding between coats if you want.

BTW, you do need primer. People often think the purpose of primer to help hide the original colour of the surface. It does help with that, but it's real purpose is to bond the new paint to what you are painting.

Thanks alot I appreciate it! :)