Question for Professional Sprayers.....

[smhmotorsport]

Been having a bit of a mare painting a TR3, and in a bit of dissagreement with the responce I got from the paint rep....
As brief as possible.. Bodywork down to bare metal and etch primed, allowed to dry for 20 odd hours. Scotched etch then 3 coats of 2k 3-1 high build primer. Wait till primer cured, guide coated then wet flat with 400. Now heres where the fun begins. When putting the base coat on, 1-1 thinners, the primer is blistering, losing adhesion from the etch. If you put the basecoat on very dry theres no reaction but if you put a wet coat on it then all hell breaks loose.
Now I think its the thinners in the basecoat reacting with the primer ( uses same thinners in both though none used in primer on this) But am I wrong in thinking 2k primer once cured should not soften ever?
The explanation I got was that its down to me wet flatting the primer and its absorbing water. This however doesnt explain why the primer flats ok, only reacts when painted over. Also when applying the 2k clear coat theres no problem at all, no reaction whatsoever. This also has the same thinners in as both basecoat and primer.
I was told no-one wet flats primer any more? Is this right? Am I living in the dark ages? I cant see how a scotch brite can get a panel flat?

Any opinions??

I got the car painted ok, just took a little longer than expected.....

[merckx]

Isn't 1:1 far too much thinners?

[Russ Bost]

I always hated basecoat for exactly this reason. If you stop & think about it basecoat isn't really a "proper" 2 pack material, it's actualy a lot more similar to cellulose where reactions of this kind where commonplace. I think what causes it is the characteristics of the basecoat itself, because, as you say the thinner is the same in both cases. I always wet flatted just as you describe & 1:1 is the correct ratio for the thinners. You don't say if you have an oven, but I suspect not, I think you'll find if the primer is given longer to cure, or is oven baked this reduces the problem (also eliminates any problem of the primer having absorbed water).
I always put the base coat on at a higher pressure than normal & drier in the hottest temperatures possible, hence it dries b4 being able to soften the 2k primer, if necessary flatting off b4 the final coat which I used to thin by another 20%. Hope this helps.

[smhmotorsport]

Thanks for that Russ. You're right I dont have an oven, though I did have the temperature up with a big space heater, and the only way I could prevent the reaction was, as you said, light dusty coats. Whats your opinion on 2K primer absorbing water? I cant quite belive that the primer once activated and cured will absorb water. If it does, what happens when you apply a topcoat of a water-based paint? I think the paint rep is grabbing at straws.. Ive painted my CRX door the same way to see what it does, though it wont be getting a base clear.

[Russ Bost]

Paint reps will clutch at any straw available rather than admit their product might be at fault!! I'm a bit out of date with the paint industy, I just use a little 2k nowadays, I've avoided water based because, as with all modern bodyshop materials, it's aimed at the bigboys with ovens/infra red etc.
With regard to 2k primer absorbing water, well, I was always told that primer was porous, but absorbent? Hmmm .............
What is far more likely is that the primer, due to not being baked thro' (a space heater simply doesn't work the same way infra red does) was probably not fully cured (I believe this can be the case even after a week or so) & the thinned basecoat was enough to interfere & cause a reaction.HTH