whitestreak3

Hello all,
I am in the final stages of preparation for paint, and I want to get my rear bumper figured out. I have already stripped down through the paint, and am now at the black factory primer. My question is: Do I need to sand all the way through the primer? There are some areas where spider web cracking is prominent. Should I just sand those areas to the urethane and then leave the rest of the bumper in primer? Will that cause some issues in repaint? Thanks!

DUB

PLEASE....ALWAYS post your year model...because I do not go off members' avatars and go searching on what you have.

If you see the spider cracks.... and can make them get more noticeable when you press on the underside of the bumper. I would sand the primer down....BUT...you have to REMEMBER....DO NOT.....REPEAT....DO NOTwipe the bumper with any solvent and especially the area that are showing raw urethane where you exposed it. There are specific water-based cleaners for urethane.

It is hard to say if these 'spider cracks' are in the urethane or not...and now knowing what year it is...they actually can be in the urethane itself.

YES...you can have an issue where the black primer was removed and leaving some of it surrounding your repair area. The solvents in the primer you need to use can get under the edge of the original black primer and cause it to lift if you are not careful when applying the primer you plan to use. It can also cause the original primer to slightly swell.

And if you are thinking that you are going to strip it all the way down....from PROFESSIONAL EXPERIENCE...when I have done this....the prep and getting the raw urethane CLEAN and ready for the primer I use is PARAMOUNT and TIMING has a lot to do with it. With the special cleaners and primer I use...when I am done cleaning the raw urethane...I LITERALLY dry it off and use my water based prep cleaner and PRIME IT IMMEDIATELY....and not allow the clean bumper to sit in the paint boot for ANY LENGTH of time due to the pores in the urethane have been opened up and are already getting contaminated....and the longer you wait...the more contamination they get on them. Think of it like you cleaning cut on your hand. Your wash it, dry it, apply some isopropyl alcohol on it because it is not a deep wound...THEN you cover it with a bandage immediately. You do not do all that 'prep' and then walk around for an hour and then apply the bandage.

OBVIOUSLY...this is MY OPINION....and many painters I know do it 'their own way'...so you can do it how ever you choose.

DUB

whitestreak3

Thanks DUB, I appreciate the help. So do I need to pick a lesser of two evils? If I take off the primer in certain areas that need repaired, there is the possibility of the surrounding primer getting lifted, and if I don't take down the spidercrack areas, the cracks will eventually just fester through my fresh paint job? And the car is a 1981, sorry about that

DUB

I can not answer this because I do not know what is going on with the bumper and if the spider cracks get bigger when you push on it form the underside..or when you take it down to raw urethane if there is a problem in the urethane itself. You what you feel comfortable with....because it could go either way. Hard to say without the part being in front of me and me working on it.

DUB

whitestreak3

Yep, I understand. Anybody else?