Self-Etching Primer thickness

I'm using SEM self etching primer with HVLP gun:

I've heard people say that you have to be careful not to apply primer too thick. I know thick primer is also a concern with it "lifting". In the past, I have applied it just until I reach an opaque green color over the part (usually 3 light coats). Is it better to have two light coats that is semi-transparent? I suppose even though you can still see the aluminum, it may be sealed already. Kind of like the wash primer that vans uses on their quickbuilds.

My problems could all be in the setup of the HVLP gun as it was my first time using it since converting from rattle can. I started out at SEM's pressure recommendation at something like 8 psi. But all that would do is spit drops of primer everywhere. I increased to 15-20 psi and it worked a lot better.

Bottom line, I need to do some experimenting on scrap before proceeding, but what were your remedies for this situation?

The SEM instructions sound easy enough to follow...

"...2-3 light coats (apply only enough to achieve hiding)..."

http://www.semproducts.com/manage/html/public/content/techsheets/sem_tds_self_etching_primer.pdf.

HVLP

Here's a starting point.
Regulator at the gun set to 23 psi.
Water/oil filter after regulator then hose.
Paint control 1 turn out from closed.
Fan control 1 turn in from fully out.

Transparent coat is fine. 8 psi would be measured at the cap. 20-25 psi at regulator is fine.

Tbone said:

Transparent coat is fine. 8 psi would be measured at the cap. 20-25 psi at regulator is fine.

Click to expand...

Why would that be better than the actual instructions from the manufacturer?

The stuff is not a wash primer.

Most wash primers/self etching primers have phosphoric acid as a etch to the substrate. They also involve no crucial film thickness. They are designed for corrosion control not film build. They need to be top coated. Naturally you would follow the TDS on the manufactures recommendations. I consider a wash primer and self etching primer as the same. Also a lighter coat would be better for weight concerns, seeing that most of our RV projects ar ALCLAD (natural corrosion "control"). Most self etch/wash primers are also solvent based and are easily removed by thinners and don't cure by chemical reaction. True epoxy based are a much better choice IMHO, but require more equipment. But what do I know, only 26 years in the paint application business! I started with the ending days of lacquer to today's waterborne processes, even a two year stint on powdercoat processes.