Paint is popping off...

[YNOT]

I've got a question for all of you paint experts.

First off...a little history on my skills. I'm a newbie when it comes to auto painting. I took a 14 week auto paint class and have since painted 2 cars and several "parts" for people...all of which turned out good and have held up fine over the past year or so.

Last summer I (and my father) painted a hood for a guy here at work. The clearcoat was flaking off really bad and he asked me if I could fix it for him.

I thought..."how hard can it be. Sand it down, repaint it and clear it...piece of cake."

Well...within the past couple of months there are little small (1/8") dots of paint popping off in numerous places on the hood down to the primer.

Here's what we did...
I sanded the hood down through most of the clearcoat...down to bare metal along the outer sides of the hood where most of the "flaking" was occuring. I used Krylon can auto primer and immediately followed it with DuPont Chromabase 2-stage paint and clearcoat, followed by wet-sanding and buffing.

What could I have done wrong?...bad paint?...something on the hood that I didn't get off completely? Anyone have any ideas? I do remember my dad wiping it with "Cinch" window cleaner as we were wet sanding...could that be it?

I wonder how hard it is going to be to redo...will I need to strip it down to bare metal and start from scratch?

[Don Meyer]

You did 2 thinks wrong:
1. when having problems take the paint down to bare metal(always).
2. Prime w/epoxy primer after etching w/phosphoric acid(ospho).
NEVER USE A PRIMER IN A RATTLE CAN.
Don

[pro70z28]

Got to agree with Don. If the paint was flaking sooner or later it will all flake so it should all come off. Also rattle can primer shouild only be covered with rattle can topcoat. I don't even like to mix brands of Sealer / Primer / Paint / Clear Coat. Best to use one system from start to finish.

[Bob Parmenter]

Ditto.

Pick one:

incompatibility - from the metal up it should all be from the same paint system.

contamination - only clean with products recomended by the paint manufacturer. Household cleaners contain all manner of chemicals that can leave unseen residue.

[SprayTech]

Well for one thing you never mix brands anymore, as all have different chemical makeups and all formulated to each brand!

Blistering

Blistering, Bubbles
Description
Blisters appear as swellings on the surface of the paint and vary considerably in both size and density.
Coarse blisters, larger than 1.5mm in diameter, generally occur in patches, although they may also be found in isolation.
Fine blisters, typically from 0.5mm rings, meandering lines or in the shape of a finger print.
Blisters in the colour coat are generally more prominent than those occurring between paint and substrate.

Cause

Moisture or contaminants trapped under the surface. This may result from:

a)_
Inadequate surface cleaning, leaving residual moisture or contaminants such as oil, industrial pollutants or grease from finger tips.

b)_
Incompatible materials or the use of non-recommended thinners.

c)_
Insufficient thickness of paint leading to increased permeability.

d)_
Water permeating both newly applied and aged films. Exposure to rain or high humidity before the finish is fully hardened increases the risk of blisters caused by permeation.



Prevention


a)_
Protect vehicle surfaces when in store, and clean surfaces scrupulously before spraying.

b)_
Use only top quality recommended and approved materials.

c)_
Follow the correct spraying processes.

d)_
Avoid exposure to moisture and extreme temperature changes until the finish is fully hardened.



Rectification


_
Establish the depth and cause of the blister by pricking out with a pin and examining under a low power magnifying glass.
Where the blisters occur between paint layers, the affected area may be sanded down to a sound surface and repainted.
In more severe cases, or where the blisters occur between the undercoat and the substrate, strip down to the substrate and repaint.

SprayTech
P.S. This web site might be of some use :
http://www.ppg.com/cr-refinish/phase...efectGroup.asp

[YNOT]

Thanks to all of you for your replies. I'll see how this goes when I re-do it.