Margal

The guy at the shop did not know exactly also why it is happening. He blames it to the plastic material and tells me that some kind of chemical reaction is going on. He suggest to fix just that spot to see what gonna happen. But most likly I think it will peel off again.
So I prefer to take the bumper off one more time, bring it and let them to strip it to the plastic. Put the promoter than primer, pre cleaner, base coat and clear?
Am I missing something with this process
Do you think the plastic material that was used for this bumper is bad and causes the problem?

tonyb635

I'm sure the material is not bad. If it was, then the entire bumper would be like this and not just one area. Polypropylene has to be painted a certain way, or the paint will not adhere correctly. OEM parts are flamed to provide the etching that is needed for the adhesion. When you order a replacement OEM part it's flamed and then a primer is applied at the OEM mfg.. The shop that receives the part then only has to sand and paint it. The adhesion promoter would not be needed unless they cut through the primered surface. The problem with non OEM parts (in most cases) they are shipped raw out of the injection supplier. I am sure they don’t flame anything and I am convinced the only reason they sprayed the coating on my parts was to hide something. Maybe flow lines, splay, who knows? The receiver has to care for this in order for the paint to adhere correctly.

My parts had a black primer looking material sprayed on it that was of very poor quality and it had to be removed. The rear had a grey primer material that was flaking and you could take your fingernail and slide across the surface and this material would just come off in flakes. I can’t imagine what would have happened if I had sprayed these in this condition. I ended up washing the parts down with a thinner to remove it and started from the substrate. It's possible that your didn't even have this stuff on your parts, or the person painting it did not realize it…

You should ask the person who painted it if they sprayed an adhesion promoter on the bumper before they painted it. That would be the first good source of info. If not, then I agree, the paint would need to be removed but that is not an easy task. If you chemically remove it you run the risk of damaging the substrate. Sanding it off might be the better way, but there are also risks that you sand into the substrate which could then show up as a wave or look like a dent. If they did use the adhesion promoter then I would have then sand the area that was peeling and feather out the broken paint edges. If the paint is not sticking well, it will start to fly off from the sander and will not feather out. They will need to sand until they get to an area that feathers properly. Clean it, apply the adhesion promoter, then apply a 2K primer, block sand and re-apply primer as needed, then apply the base and clear. If this a shop, they should know this though.

balbs

+1 especially on the flaming process. One of my hobbies is RC Helicopters and their canopies (body) are typically made out of PP as well. For prepping, I sand the surface first until everything is smooth. Sanding also removes some of the oils on the material. Once it's smooth, do a final flaming. Basically you run an open flame along the surface to burn off more surface oils and then use some adhesion promoter such as Bulldog. After Bulldog, then primer. Multiple coats of primer and even sand the primer smooth and then paint.

The canopy is installed, removed, and flexed constantly for maintenance and not a chip or flake on the paint....unless I crash.

ncsugrad2006

And most OEM's require parts be painted fairly quickly after flame treating.. within a few hours in some cases, so it's not like a supplier can flame treat a bumper then send it to a body shop a few weeks later to be painted

I have seen plastics where even ad-pro primers will not adhere. It needs to be flame or plasma treated. Usually talc filled stuff

In this case I would guess that they are not prepping the part correctly and/or using the wrong primer. I would look at the chips under a microscope to figure out which bond is failing, that should confirm where the problem is

Margal

I see only plastic and nothing on it without the microscope.that means that the first step, primer is not bonding on properly? I let the guy to treat the damaged area to see what happens and if it won't work then they have to send it and go through all steps of prep. again

tonyb635

Yes, after flaming, it's rather quick (minutes) before the adhesion promoter is applied. Actually, its pressure washed, then goes into a drying oven, robotically flamed, adhesion promoter, primer, base and clear applied robotically as the parts traverse through the process. Most all of the paints now are waterborne so the process is a little different but quite similar. The flaming process is not needed by body shops because they apply a different type of promoter which provides a nice tie between surface and paint. It's clear, so I am sure you would not see it on the surface of your bumper. From a body shop side, it's important that they clean the part well before sanding, otherwise you risk sanding the contaminates into the part. Mold release is used in the injection process and these parts are not cleaned before reaching the customer. It's not like there is oil or release dripping off of it, but if you were to apply paint material without first cleaning, you would run into some problems. I hear of some people flaming the parts, there’s even a YouTube video, but you have to be careful since the process of flaming is very specific to the type of polypropylene being used. If the person is flaming and starts to see the surface wet, then they have overdone it. It really makes no sense to flame afterwards since the adhesion promoters work well. You can get SEM or Bulldog, even in a spray can. I've used both and have never ran into any issues with them.

ncsugrad2006

Power washing, not pressure washing . CO2 cleaning is what BMW is using in a lot of places now in place of power washing

tonyb635

Yes, yo are correct, that was the wrong word to use.