Rebel Racing wrote:

dkbautosports wrote:I tend to agree with what NFT5 is saying!

you can use an epoxy primer on most plastics but not all and when you do you need to watch your mill build of your primer. in fact with most any primer you need to be careful not to lay down to much primer.

however you are missing some info on key points.
was the bumper a new replacement or a repair on the OE bumper?
what did you sand the bumper with before you primed it?
was any type of plastic adhesion promoter used?

with new bumper I will 1st give them a good cleaning .
if it's a raw bumper I will spray a coat of plastic adhesion promoter.
with a pre primed or raw I will then spray a coat of sealer then wet on wet go right to top coats.

there should be no reason to spray a bumper with a fuller or a build primer unless your priming over a repair. if your priming over a repair I still will only spot in the build primer just where the repair area is and not the whole bumper.


with your bumper if the primer is coming off in one area I'm wondering how the adhesion is for the rest of the bumper.

Probably will miss some info but here it goes: Friend of a Friend brought me some repeat business in the form of 2 bumper covers. Did the work back in April. If memory serves me, it is from a mid '80's VW something or other. OEM part that other than the usual nicks and scratches was in decent shape for the year. I likely hit it with 500 wet and then a sealer coat of epoxy before the base. The more I think about it, I don't think I used an AP. I wonder if he dropped something on it during the install and a crack started to form? At any rate, I will make it right. I don't think the owner is ticked off as he is asking if I can do some rust repair on his other car.

GOOD attitude on making it right on this one.
Jay D.

badsix wrote:

Rebel Racing wrote:

dkbautosports wrote:I tend to agree with what NFT5 is saying!

you can use an epoxy primer on most plastics but not all and when you do you need to watch your mill build of your primer. in fact with most any primer you need to be careful not to lay down to much primer.

however you are missing some info on key points.
was the bumper a new replacement or a repair on the OE bumper?
what did you sand the bumper with before you primed it?
was any type of plastic adhesion promoter used?

with new bumper I will 1st give them a good cleaning .
if it's a raw bumper I will spray a coat of plastic adhesion promoter.
with a pre primed or raw I will then spray a coat of sealer then wet on wet go right to top coats.

there should be no reason to spray a bumper with a fuller or a build primer unless your priming over a repair. if your priming over a repair I still will only spot in the build primer just where the repair area is and not the whole bumper.


with your bumper if the primer is coming off in one area I'm wondering how the adhesion is for the rest of the bumper.

Probably will miss some info but here it goes: Friend of a Friend brought me some repeat business in the form of 2 bumper covers. Did the work back in April. If memory serves me, it is from a mid '80's VW something or other. OEM part that other than the usual nicks and scratches was in decent shape for the year. I likely hit it with 500 wet and then a sealer coat of epoxy before the base. The more I think about it, I don't think I used an AP. I wonder if he dropped something on it during the install and a crack started to form? At any rate, I will make it right. I don't think the owner is ticked off as he is asking if I can do some rust repair on his other car.

GOOD attitude on making it right on this one.
Jay D.

Should not be a bad repair. I look at it as a learning experience. Owner seems cool about it and has asked me to do a fender and a deck lid also (from another car).

I've been in this buisness for around 50 years started when i was about 25 in a shop at my home. i did everything from model cars to airplanes to tugboats and appliances and everything in-between. i NEVER left a job that i wasn't totally satisfied with and the customer was also. i don't think i ever had a comeback in all that time. i did have a lady that came back because she had scratched her door about a month after i had repainted the complete car. i fixed it and told her there was no charge. i've adjusted doors free and so on, that got me more good advertisement than any i could buy. the bottom line is one bad job or not addressing a problem correctly can kill you and you reputation.
Jay D.

Jay's nailed it, again.

badsix wrote:I've been in this buisness for around 50 years started when i was about 25 in a shop at my home. i did everything from model cars to airplanes to tugboats and appliances and everything in-between. i NEVER left a job that i wasn't totally satisfied with and the customer was also. i don't think i ever had a comeback in all that time. i did have a lady that came back because she had scratched her door about a month after i had repainted the complete car. i fixed it and told her there was no charge. i've adjusted doors free and so on, that got me more good advertisement than any i could buy. the bottom line is one bad job or not addressing a problem correctly can kill you and you reputation.
Jay D.

Totally agree. I'd never let something leave here that I was not happy with. I've even kept parts a a day or 2 longer than the owner liked just to make it perfect and when they got it back, they have always been happy.

It sounds like you're already on the right track with your thinking. Flaking paint is often a sign of contamination or poor adhesion, and contaminants left on the surface are a common culprit. Here are a few things to consider that might help pinpoint the issue:

Contamination During Prep: Even if you were thorough in your cleaning, sometimes contaminants like oils, silicones, or wax residues can be stubborn and hide in small crevices. Make sure to use a high-quality wax and grease remover and follow up with a second wipe-down using a clean cloth. Also, make sure you’re using fresh towels to avoid reintroducing any contaminants.

Insufficient Surface Prep: If the bumper cover was made of plastic or had an existing coating, it might have needed additional prep to promote adhesion. Sanding with the appropriate grit (like P320) and using a plastic adhesion promoter or flex additive before applying epoxy primer could help the paint adhere better, especially if the surface was slick or glossy.

Flashing and Curing Times: Check if the epoxy primer had enough flash time before the basecoat was applied. If the primer wasn't fully flashed off, it might have caused the basecoat to lift in spots. Also, check the paint and clear coat manufacturer's guidelines for flash times, as rushing this step could lead to adhesion problems.

Spot Repair and Blending: For the spot repair, clean the area thoroughly, feather-sand around the flaked-off spots, and make sure you prep the surface well. Apply a fresh coat of epoxy primer if necessary, then carefully blend the basecoat into the surrounding area. Make sure to use a blending reducer and apply a new layer of clear coat over the entire panel for a seamless finish.