Paint adhesion between layers?

[julianf]

I've had a job where I've had issues between the layers of paint -

This is single stage 2k. Not base and clear.


Wet on wet primer / top. Wasn't happy with a few bits so sanded, and recoated.

Then the fly...

So now I'm sanding the second coat and getting delamination between the first and the second. A step with a bit of thin flaking on the edges.

So far as I'm aware I scuffed it all up between first and second, but maybe I didn't? What else could be my issue?

Thank you.

 

[ajlelectronics]

I've had a job where I've had issues between the layers of paint -

This is single stage 2k. Not base and clear.


Wet on wet primer / top. Wasn't happy with a few bits so sanded, and recoated.

Then the fly...

So now I'm sanding the second coat and getting delamination between the first and the second. A step with a bit of thin flaking on the edges.

So far as I'm aware I scuffed it all up between first and second, but maybe I didn't? What else could be my issue?

Thank you.

Either you forgot to key it, or surface contamination.

 

[richie00boy]

Did you sand it or scuff? What grade/colour pad?

 

[julianf]

Did you sand it or scuff? What grade/colour pad?

Sanded, with 800. Hard backing pad.

I'm laying on thick paint (orange peel is desirable on these as it hides fingerprints etc in use) so could probably go down to about 5 or 600 before the sanding marks show though, but I'm pretty sure this was done with 800, as that's what I had close to hand.


The things I'm doing are folded boxes, and I find that the plastic wire pad things (don't know the correct name - like the green stuff on the back of a sponge) tend to get caught on edges / between folds and then I'm picking out bits of plastic.

 

[steveo3002]

sanded until dull yes?

should have worked fine , strange one

 

[ajlelectronics]

I'm laying on thick paint

That can be another issue, it traps solvents. Try lighter coats at lower pressure to get the effect you want.

 

[MG David]

Were you using a fresh sheet for sanding or had it been used before?
Sometimes the odd bits around the workshop have become contaminated.

 

[MetalMonkey]

Personally, I sand back existing paint with 400, but that is a DA, so you end up with a smoother finish.
Wet on wet top over primer - was it epoxy?

Thick coats might be the issue. If you are scuffing with 800, you shouldn't need a very thick coat to cover that. Did you do it wet or dry?
How long did you leave it before recoating?

 

[steveo3002]

on fresh paint a tickle with a scotch pad ought to provide a good key

 

[ajlelectronics]

on fresh paint a tickle with a scotch pad ought to provide a good key

Agreed, but laying it on thick can trap solvent between the coats.

 

[steveo3002]

are you thinking its skinned over and left it uncured between layers?

 

[ajlelectronics]

are you thinking its skinned over and left it uncured between layers?

That is my supposition, if it was flatted beforehand. Might be nonsense, but I can't think of another cause for adhesion loss of the same material when prepped correctly. 2K is a chemical reaction but it still needs to flash off its solvents during the cure.

 

[norsa]

I'm a tad lost here. If you went wet on wet, why are we discussing flatting back?

 

[MetalMonkey]

I'm a tad lost here. If you went wet on wet, why are we discussing flatting back?

I think he means first topcoat was put over wet primer.
Second topcoat was put over dry but sanded paint.

 

[norsa]

Very odd. Wet on wet should adhere if within the tds window. If that's keyed, a subsequent coat should adhere. So which layer is not bonding?

 

[julianf]

If you forget any mention of wet on wet, then it may be clearer -

I'm taking about the lack of adhesion between a coat on top of a fully cured prior coat.

 

[norsa]

Aha. Gotcha. Can only be a lack of sufficient key or lack of tack then.
Nick

 

[julianf]

Lack of tack?

 

[norsa]

Did you tack the flatted substrate before you applied the second top coat?

 

[julianf]

Tack cloth? No.

Dusted with a microfibre and then blown over.

Could that be my issue? Fine dust remaining?

I have not been using panel wipe, as the parts are (usually, although I guess I may have delayed this time?) painted direct from sanding, so, my thinning is, any minor contaminants will have been abraded away.