Production painter types, I have a problem

I had a buddy that stopped by and wanted me to help him with his wife's late model. It seems she has backed into something with that new fangled plastic bumper. So we sanded it down and sprayed it with the SEM flexible primer.(don't ask me what I think of that stuff), wet sanded it and sprayed the first stage of the bc/cc. The base is Dupont chroma base. After we sprayed the color, the plastic started to raise the grain, for lack of a better term.

It was smooth before we started spraying, now it is rough in areas and you can see the sand marks. Weird. So here is my dillema. Should I wetsand the base and spray it with DP -LF as a sealer? Or will the DP pull the chemicals and cause it to solvent pop? It looks like hammered Dog Sh#t.......

I don't wanna waste anymore color trying to fill imperfections and sand scratches. I think the plastic is sucking the chemicals out of the bc.

Thanks

 

I dunno but sounds like maybe too heavy on the coats and it penetrated and lifted. at this stage its going to be a bitch but you gotta sand it down and minimize the break through and then prime again but dry coats with plenty of flash time between coats ,base too,the solvent can penetrate if it lays there too long. hope this helps ya man.

 

Well, it didn't actually lift. As soon as paint hit the areas in question they looked funny. It looked like it never was sanded.

 

like rafman said, the solvents in the basecoat reducer probably loosened up the primer,,,,

wet sand it and DP (you can reduce the dp a lil with DT reducer)
you should be OK,,.,..

 

I'll seal it in the a.m. I just wanted to make sure that the DP would seal it up. That plastic stuff sucks.

 

Repairing Plastic Bumper Covers Can Be Difficult Due To The Many Different Types Of Plastics Used To Manufacture These Parts. Tpo Being The Most Difficult As This Material Requires Very Specific Procedures .when Not Completed Properly Symtoms Similar To What You Are Describing, Can Be Expierenced. There Is A Specific Cleaning Process Along With An Adhesion Promoter That Must Be Followed On This Plastic Even When Applying A Repair Material Such As Sem. The Problem With Tpo Is That The Manufacturors Mix A Silicone Mold Release Agent Into The Plastic During The Injection Moulding Forming Of The Part. Tpo Has An Oily Feel To It And Usually Has A Black Color . Gm , Honda Are Major Users Of This Material.
Sand Scratch Swelling Is Also Another Difficulty Expierenced From Time To Time.the Repaired Raw Plastic Should Be Finished In A 180 Grit Paper. A Good Trick That I Was Taught Many Years Ago In The Shop Was To Take A Rag Soaked With Laquer Thinner And Wipe The Repaired Area Before Applying Any Additional Repair Materials Or Finishes . If Something Is Going To React ,this Step Will Cause It To React Before You Have Spent All The Efforts To Prepare The Area For Refinishing.

Has This Cover Been Repaired Before This ?

 

Yes it has. It is the black plastic. I have some of the adhesion promoter SOMEWHERE lost in my shop. We wiped the plastic down with lacquer thinner but I didn't leave it sitting on it very long. We'll be on it again in the morning. Hopefully, I can seal it up with DP just to get some even color on it. He is planning to peddle the car in the near future, so he doesn't really wanna spend too much time on it.

 

There Is A Plastic Cleaner That Needs To Be Applied Before The Adhesion Promoter. The Silicone Release Agent Must Removed Or It Will Not Stick. Check The Sem Website They Should Have Detailed Procedures Posted .

 

Man, if you want people to read what you have taken the time to write and take you seriously, do yourself a favor and stop capitalizing EVERY word. It's very difficult to read and downright annoying.





Roothawg, did you get your problem figured out? I sounds like sandscratch swelling. This usually happens when the sandscratch's are too deep and the basecoat is applied too "wet". Lighter coats help, but the basecoat will still shrink down into the scratches and show up later if the color is a lighter metallic. I usually don't apply anything like DP over the area because this just adds more solvent to the sctratch. I like to just wetsand the area down and proceed with light coats of base. When you start wetsanding, you'll probably notice that the areas that were swelled up have now shrunken down below the main surface area. This is because the solvents that made it swell have now evaporated making the basecoat shrink.

Anyway, hopefully you have the situation under control by now and you won't need this information.

 

Either he is very fast with is pinky finger, or (if he picks and pecks like I do), it takes him forever to type a message!

I just redid one of these myself, on my grandfathers 2002 cadillac. Anytime you sand into the black plastic, its a nightmare to fix. He hit a few things lightly with it, and the factory paint was cracking and peeling off, so I sanded down to bare plastic in most areas, especialy around the corners, and anytime that I went a little to far into the plastic with 80 grit, it tore the plastic. Those areas kept coming back after priming. It seems that the plastic is pourus (sucks paint like a sponge), but there are 2 different layers. The outer layer, or some sort of a coating takes paint well, sand through it, and it soaks it in.

I noticed it in the primer stage (luckily), and coated the whole thing with 2 wet coarts of DP(lf)90, wet sanded that, a coat of primer, wetsand, and then bc/cc, and it worked out great.

 

If you didn't properly wash the area prior to sanding; (soap & water before a
good solvent wash), you can grind all sorts of contaminates into the plastic.
They'll always jump up and bite !

 

Thanks for all the advice guys. I got up this morning and wetsanded the whole plastic cover again and sealed it with DP in very light coats, allowing plenty of flash time inbetween. Then I proceeded to do the same with the color and the clear. As of 4:00 pm we are still good. I am gonna go peek at it now and hope it still looks ok. This just re-enforces my love of steel.