respray bumper / paint peeling

[tricky12]

Recently tried to repaint my bumper.
1st used u pol grip 4 followed by a 2 pack high build primer then top coat of 2 pack straight gloss black.

The problem i have is when i removed some of the masking it pulled off the top coat. It appeares that the top coat has not adhered to the primer beneath.

What is the cause and what action would you recomend, the problem seems to be between the two paints and not the surface of the bumper.

[Anatol]

Adhesion failure between layers of refinish materials is usually down to:

Improper key - if your primer layer was intended to be flatted back before overcoating, not doing this, or using the wrong grit for the next coat's needs,
Over-curing - spraying a solvent-based paint coat over a non-sand primer layer, adhesion depends on the primer not being 100% cured - applying the paint during the right window causes the two layers to bond together and then cure into a single layer,
Flatting residue - if you flat the primer, and leave the dust on (even wet flatting and letting the flatting residue dry on rather than cleaning it all off) then the paint layer adheres to the dust, not the primer, and the topcoat can flake off,
Wrong spray technique - if you apply the paint in coats with the wrong distance, with the wrong atomisation (including air pressure) then the paint can lose its solvent before landing on the panel - so it lands as dry dust, and fails to properly adhere,
Wrong ambient temperature - if too cold, the paint viscosity is higher, so it doesn't flow into the same keyscratch as well, and the surface area of contact is lower - so adhesion is compromised, and if too hot, the panel or ambient temp can accelerate the solvent flash-off out of the paint, having the same effect as above, dry dusty paint layers, not properly bonded.

Or any combination thereof.

HTH

[tricky12]

Ok this make sense in the way that i did it.
But now what would be my best cause of action start again right back, or flat back to primer and use a grip coat and then paint, or flat back again to primer leaving a rougher finish, or something totally different

Thanks

[Anatol]

Definitely remove all the paint layer that has compromised adhesion. What to do next depends on the materials you're using... Can you let us know what the products are, and what their TDS's recommend as the refinish process?

[tricky12]

Ok this make sense in the way that i did it.
But now what would be my best cause of action start again right back, or flat back to primer and use a grip coat and then paint, or flat back again to primer leaving a rougher finish, or something totally different

Thanks

[tricky12]

Not exactly sure what you need but here goes
U POL HS Primer filler rub down 600 - 800
churchill acrylic 2k jet black

Also wondering if temperature was another factor as did it in the garage last week with the door half open

[tricky12]

Not exactly sure what you need but here goes
U POL HS Primer filler rub down 600 - 800
churchill acrylic 2k jet black

Also wondering if temperature was another factor as did it in the garage last week with the door half open

[Anatol]

Ok, Churchill don't suggest a keyscratch on their TDS for their 2k colour, but 600 should be ok, though many 2k's suggest 400 (or red scotch) as the key.

The other thing that makes a difference is pot life - the paint should be applied immediately after mixing really, as it starts to cure in the gun, which affects viscosity, which affects how it keys.

I'd suggest removing all the failing finish, keying up with red scotch, thoroughly cleaning down and degreasing, and reapplying your paint at about 20 degrees, when freshly mixed, with the gun set up to spray the right pressure and distance.

The product in question has isocyanate in the hardener, so protect your lungs properly, and do not spray under any circumstances if anyone else without the proper protection could be affected by the spraymist. These aren't use-near-the-public products. If you're painting a full panel, or using a full size gun, using more than 25ml of paint per coat etc then the HSE consider that this stuff CANNOT be safely and legally sprayed outside or a proper enclosure or booth, so do take care to look after yourself and others nearby.

[tricky12]

Ok thanks very much for all your time and help will give it a go.
thanks again

[tricky12]

Thanks Anatol for your help, everything seems good.
Removed the bumper from the car this time meant that i could get some heat on in the garage and get right to the edges of the bumper, got all the peeling paint off flatted and red scotch all over then turned up the pressure a little on the compressor and used a different spray gun and perhaps added a bit more thinners and that was it.