hi everyone im new to the forum. im a technician by trade but like to a bit of bodywork. small bits here and there. i have a ford focus and wanted to put the standard spoiler on it so purchased one but the wrong colour... not a problem so i sanded it down and primed it. however here is the problem everytime i lay down a coat of primer weather its 1st coat 2nd or 3rd the paint keeps cracking!!! its keeps cracking along the edge of the sanded down paint underneath. the paint on the spoiler isnt new its old paint so i didnt think it could be a reaction with that... have a look at the pictures and if anyone knows could you please share your knowledge!! thank you.

What kinda primer are you using? Need to know that. Brand and number please.
You need a barrier coat. Your new paint can react with old paint. Any time you sand old paint your new topcoats solvent can attack the old finish. Your having a lifting problem due to a chemical reaction. Several variables could be going on. Kinda primer matters like if it's Laq primer or not.

Truth is sometimes it's really hard to tell why your having a reaction, but you are. So fastest solution would be sanding it back down and barrier coating it, and then finish with the rest of the steps.

UPOL makes a great barrier coat upol720. Or go to your local paint place in the UK and see if they have a clear barrier coat.

Thanks
Tammy
Tamco

TamcoPaint wrote:What kinda primer are you using? Need to know that. Brand and number please.
You need a barrier coat. Your new paint can react with old paint. Any time you sand old paint your new topcoats solvent can attack the old finish. Your having a lifting problem due to a chemical reaction. Several variables could be going on. Kinda primer matters like if it's Laq primer or not.

Truth is sometimes it's really hard to tell why your having a reaction, but you are. So fastest solution would be sanding it back down and barrier coating it, and then finish with the rest of the steps.

UPOL makes a great barrier coat upol720. Or go to your local paint place in the UK and see if they have a clear barrier coat.

Thanks
Tammy
Tamco

Hi thanks for the quick reply. im usuing u-pol high build 20:20 primer. i went back to the garage and scraped threw one of the cracks with my nail and the paint underneath is like i have put paint stripper on it so its 100% a chemical reaction i just didnt know how to stop it!. thats great to know. as i had this same problem on a past project and in the end i just sanded back to bear metal!! step i have obviously been missing out!! but how comes sometimes this doesnt always happen? :\. thanks for the help tho should be an easy fix. fingers crossed. also can you spray a barrier over filler to stop it looking like an island underneath ? thanks. luke.

The best solution would be to strip it.
Its not a good idea to "cover up" a low quality paint like what you have on there. Most of the time you have more problems later on. (If you start with "Crap" you will end up with crap!)

I agree. but what is the best bay to strip it its made of plastic and has some tight edges on it. sanding wise I don't want to go too far with it because it's plastic I don't want to deform it. will paint striper be ok. then use a plastic primer - high build / filler - guide and paint ? thanks. luke.

Anyone ????