Paint a plastic bumper cover

Answer 1

Painting an aftermarket plastic bumper cover can be tricky mostly because of the waxy mold-release agents that are molded into the plastic. Even if the bumper cover is primed, you will likely have adhesion problems or fisheye if you simply basecoat+clear over the top.

It's always preferable to find a junkyard bumper cover and just repaint it, but if you must use an aftermarket bumper cover here are some things you need to know:

NOTE: Wax and Silicone are your enemies here and you must vanquish them to achieve adhesion! The Silicone will only be on the surface so with good prep, you will get it off, but the wax (mold release) is literally mixed into the plastic and makes up about 5% of the material, so there is no getting rid of it completely - however you can whip it into submission, more or less.

First scuff the plastic (ALL OF IT) with a scotch brite pad and wash thoroughly with soap and water. If the water beads up on the bumper, it's NOT CLEAN. Water should sheet.

Next you will need a product called "Total Prep" or equivalent. It comes in a spray can. This is another 'cleaning' step. Use a CLEAN Cotton cloth (do NOT use a paper towel!!!) that has no hint of grease, wax or anything like that. If you wash your cloths, stuff like fabric softener and dryer sheets contaminate the cloth and will contaminate your bumper! Do not let the Total Prep dry on your bumper - wipe it off - the idea here is to remove contaminates, not to just move them around. Keep cleaning until you come out with a nice, clean rag. It may take a few rags.

Once you've thoroughly cleaned with total prep and it is dry, wait no longer than 30 minutes (otherwise wax will begin to re-emerge) and apply your next product (this is assuming you're in a dust-free environment - if not make sure all dust is removed before proceeding.) This is called "adhesion promoter" and it's available from 3M (5907) or in a product widely used called "Bulldog."

Follow the instructions on the adhesion promoter to the letter. Spray it on, wait about 10-15 minutes and it will flash (turn hazy) and now you're ready for the next step. Some may consider this "belt and suspenders" but if you want to be SURE you have superior adhesion, do it: use SEM 39133 Surfacer (this is a type of primer) as opposed to any normal primer you might want to use. This product is designed for this type of operation and will save you hours of grief. Your first coat should be light, and you should apply at least three thin coats. Do not sand in between unless you have a surface problem that needs to be addressed. Again, always read the product directions first and follow them.

Now that you have an opaque primer finish (you can't see through it anywhere) and it has dried thoroughly (don't push this!) you're ready to move on to the next step. You're ready to use a more 'standard' type sanding primer and this you will use for building up the finish. Be very careful not to sand through this primer coat and into the SEM primer... just build as needed and always use medium coats; not too heavy or they might take too long to dry and while sitting there, eat into base layers and allow the wax to come up. Take your time and don't push it. Use 400 grit between coats.

Once you have built up the primer coat to perfection (trust me, anything you can see in primer will look many times worse in paint!) final sand with 600 grit. It should look pretty nice - no fisheyes, no crazing... if you have that, somewhere you didn't follow the instructions!

Now you're ready for basecoat and clear, but remember to use a flex additive to BOTH the bc and the clear and as always, don't apply too much paint until the last clear coat.