Using spray primer, getting tiny bubbles

[Alan Berezin]

I am sortof a newbie (been doing wwing for about a yr). Im building a large builtin and currently doing the doors (frames made of soft maple). The whole thing is getting painted using an oil based paint. The process I have been using, successfully, is this:

Sand down to 220
Prime with Kilz original (spray can)
Sand lightly with 220
Spray thinned oil based paint using HVLP gun (cheapo conversion gun)

The whole process has been working fine until this weekend when I was doing the doors. When spraying primer, I was getting tiny bubbles that formed on the surface. Most of them popped leaving tiny craters that had to be sanded out.

The only thing different is that it is now hotter (texas) and more humid. Does anyone know why I get this bubbles and how to prevent. I guess I could try shooting the primer from my gun but spray cans are soooo convenient

[Ken Fitzgerald]

Alan..........I'm sure that some here with more experience than I will respond but.........How long has the wood been in the area where you are spraying? Has it had a chance to acclimate? It sounds like the temperature of the wood is rising...causing it to expand and cause the air to be expelled. Just a thought.......

[Phil Phelps]

You need to drain your compressor tank and use a regulator at the end of the line. You should also have an inline regulator and moisture trap at the end of your gun. This could be your problem since it's humid as all get out in Texas.

[Steve Clardy]

Tiny bubbles. Where have I heard that before? Some song I think

Yes. May be a moisture issue.
Are you stirring it or shaking it before applying?

[Todd Burch]

Sounds like too dramatic a change of temperature. Did you spray out of doors in direct sun? Or, after spraying in the shade, did you place the door in the sun to dry "good and fast"? I've had this problem before, and it's always a user error - whether too much moisture in the line, or too hot of air from the compressor, or having the paint or primer flash to a skin too fast while the wood is still heating up, then thus, releasing gases imbedded in the wood.

Do tell.

Todd

[Alan Berezin]

Thanks for the tips. The primer, which has the bubbles, is from a spray can, not my gun. So while I may need a moisture trap (when I drain my compessor, water does come out), that is not the problem in this case. I do shake the can as recommended by the instructions (and which has not caused problems in the past).

Next time, Ill do an experiment. One test piece will be left in the garage (hot, humid) and the other in the house for a few days (cool, dry). Then Ill prime each one.

[Alan Berezin]

The whole process was done in my garage. I would estimate the temp was 95 deg. The wood parts were waiting in a garage to get sprayed and so they were at the (air) temp of everything else in the garage (including the spray can). The parts stayed in the garage after spraying to dry. I am guessing that the temp was just too high for this process.

[Allen Bookout]

Alan,

For the first time ever using Minwax clear poly I got a couple of coats with tiny air bubbles. No shakeing but stiring slowly to assure no air bubbles in the poly and applying with a new brush. Your weather has been simular to ours lately with very high humidity. My garage door has been open quite a bit to try to keep it a bit cooler so it had plenty of chance for the moisture to invade the interior. I am thinking that it is not the temperature that is the problem but the humidity. I did another piece this afternoon after the door was closed for several hours, overnight as a mater of fact, and the problem seemed to have disappeared.

Could be just a coincidence but it seems strange that both of us had the same problem arise at the same time with simular weather even though they are different products applied with different methods.

Allen

[Alan Berezin]

I am curious enough to do a little test this weekend. Ill take one peice of maple and leave it in the AC'd house for 24 hrs. Another Ill place in a sealed container with a moist rag and left outside (presumably 100% humidity in the container). Ill then spray each and see what happens. Ill let you know.

[Ken Fitzgerald]

Alan........Hoadley in his book Understanding Wood talks about IIRC having bubbles appear in his finish when he brought wood up out of his basement into the house to finish. Just a couple of degrees in temperature increase caused the wood to expel air and create the bubbles. He was putting on some type of clear finish and he was able to sit and observe it. One moment there were no bubbles and while he was watching ....they appeared. One would thus think that the opposite would hold true too! If you took a piece from a warmer temperature to a cooler temperature, you could diminish the possiblity of bubbles forming?

[Alan Berezin]

Very plausable however the wood in question had been sitting in the garage for a long time and was not moved. The spraying was done midday on a rather hot day so I suppose the garage itself, and everything in it, was rising in temperature.

I think I might get myself one of those spiral recording temp and humidity deals. Would be interesting if nothing these to see what is happening if nothing else.

[Steve Clardy]

That will happen to me once in a while with oak. Build a door, whiz it [them in the finish room] may be cooler, warmer.
Spray first coat of lacquer, put the gun up, then see tiny bubbles appearing. I think its the air captured in the wood. But may be temp related also, as my finish room is well insulated, door is kept shut. 6" sidewalls, 20" blown in in the ceiling. It will stay cooler in there all day if I keep the door shut.