I need some paint help!

[Roberts280Z]

I'm trying to paint my 280Z.  I'm painting individual panels so that hopefully I'll develop better technique when I get to the main bits.  I've done urethane primer, and have just started the basecoat/clearcoat on the liftgate.  I think the basecoat went on well enough.  But, after the second coat of clear, I noticed some imperfections.  Here is a picture looking into a floodlight reflection that accentuates the imperfections:

There is, of course (for me), a bit of orange peel, but I would be happy with that if that's all I had to cut.  But you'll notice the 'big dipper' star constellation just below that , which appear to be a set of stalagmites rising up.

After some 1200 grit, the stalagmites are reduced to donuts:

This is an extreme close-up showing 2 of the stalagmites.

I've tried to read everything I can find on this, and I'm concluding that these are air bubbles caused by inadequate atomization, which itself is caused by too-low gun pressure, or holding the gun too close to the surface.  I don't think it's fish-eye-style contamination (been there and done that).  Does that look right, or is this something else?

Thanks in advance for your help.

Robert

 

[Patcon]

What is your air source?

How are you drying it?

[Mark Maras]

Or are they fish-eyes? They can be caused by Silicone, wax or oil under the paint.

[Roberts280Z]

Thanks for the comments.

Patcon, you have a good point about the air. I'm using a cheap in-line drier right at the gun, and the humidity here in Houston has been 110% for the last few days. I have had situations where the gun would literally drip water droplets, making huge puddles in the paint. But perhaps there are other variations on the water problem. Better drying solutions are a good bit more expensive, but I will look into it before I do much more.

Mark, I've had fish-eye experience before as well, when I didn't properly prep the primer with a proper wipe-down with liquid sander or the equivalent. But my experience was that the fish-eyes formed immediately while you're spraying.

I've got the inside of the doors that I can experiment further on before I do the more critical parts.

 

[Patcon]

When drying air, remember the air is hot coming out of the compressor. The smaller the compressor, the hotter it is. It needs distance to cool. More line or hose will help. You need a regulator at the gun to make sure you can get the gun set properly. You can also run a couple of loops of hose through a cooler full of ice. Then put a water trap right after the cooler. Then a desiccant dryer right near the gun. You need good dry air or you'll struggle to get good results. It sort of looks like a water spit to me but it can be hard to tell remotely

[grannyknot]

Those bumps could be caused by a few things, as mentioned above too much water in the air stream, it could be trash that dropped on to the surface or out gassing.  What is under the Urethane primer?  Did the primer get enough time to cure before the basecoat was applied?  Your second pic shows that you haven't broken through the clear to the colour coat yet so it appears the problem is isolated to the clearcoat layers, but hard to tell from just 2 small pics.

As long as you have enough clear on 3-4 coats you could also sand your way to the bottom of the bumps and still save the panel.

[Roberts280Z]

Thanks again.

The urethane primer is over a variety of surfaces - an older, roughed-up repaint, some filler topped with rattle-can high-build primer, etc.  The primer was sprayed on a couple of weeks ago.

I'm looking around for more drying solutions.  At the moment, I have a small desiccant dryer at the gun, feeding a regulator at the gun.  I was indeed able to sand down the donuts with some clearcoat left.

[Patcon]

Also if the air is really wet, the dessicant filter will get saturated quickly. Typically the beads inside will be pink when wet. I dry my desiccant in the oven on 200f until they are dark blue. Then reuse them

[grannyknot]

This is a quick and inexpensive way to cool the air coming from the pump and drop the water out to be drain at the bottom of the tank.  The A/C condenser is from some mid 90's Honda.

 

 

[siteunseen]

54 minutes ago, grannyknot said:

This is a quick and inexpensive way to cool the air coming from the pump and drop the water out to be drain at the bottom of the tank.  The A/C condenser is from some mid 90's Honda.

 

 

You can pipe that in the outgoing line from the compressor? In through the condenser and then out to your tool? Never seen that before but what a great idea. I've struggled with moisture in my line for years. Mainly sandblasting.

[siteunseen]

For only occasional use what about a copper coil in a bucket of ice?

[Patcon]

Both are excellent ideas