I didn't shake the can or the spray cup; I poured the poly from the
original can into the cup, added a bit of thinner and swirled them
together (only about 2" of material so it was easy to swirl). The
finish doesn't look like it has bubbles in it like when I've used
straight poly with a brush. That method always used to leave a lot of
entrapped air. This issue with the second coat of "pinholes" are very
tiny pin prick sized depressions with no surrounding gentle depressions.
AND of the 4 drawer fronts I sprayed, the first two were the worst,
the third is so-so, the fourth looks really good, and so does the desk
top which I sprayed after doing the drawers.



dave

JGS wrote:

Hi BAD,
I did a lot of reading when I first bought my sprayer and all though I
never experienced it in person, one author mentioned "Micro bubbles" in
poly. These would be caused by shaking not stirring the mix and would result
in pinholes. IMHO this James Bond kind on thinking is bull but then I have
been wrong before. Cheers, JG

Bay Area Dave wrote:


I put the first coat of poly on my desktop and it looked fine. Here are
the facts pertinent or not:

1. Thinned about 10% with Low odor Mineral spirits from HD. - Minwhacks
poly.
2. Applied at 66 degrees with 8# pressure HVLP .041 tip.
3. Looked fine and dried enough in 4 hours to sand lightly with 220
grit, per instructions on poly.
4. Wiped off surface with mineral spirits (damp) and wiped again with
dry rag.
5. Applied second coat with same parameters as above.

On the first 3 pieces I sprayed, there were obvious little pinholes in
the film that weren't there during the first coat.

QUESTIONS:

I'm sort of suspecting the sandpaper. It is Norton's new line of 3X 220
grit. It's yellow and very flexible. Even though it says it's for
between coat sanding, I'm wondering if it has sterates in it. It says
nothing about sterates, but wouldn't that cause pinholes in poly?

I JUST WENT TO THEIR WEB SITE AND FOUND OUT THERE ARE STERATES IN IT.
WILL THAT SCREW UP THE FINISH??

Oddly, the last thing I sprayed was the desk top and it didn't look like
it had pinholes in it. I sprayed a bit onto scrap before spraying the
project, in order to set the spray pattern and volume. Even so, COULD
poor mixing of poly and thinner in the gun cause the first few items to
have pinholes? I resprayed them again and still could see pinholes.

What do you think went wrong?

Can I fix this for the next coat by using naptha or some other solvent
as a final wipe instead of mineral spirits?? What solvents would be safe
and effective for between coats?

dave