Pinholes In My Clearcoat!?

[stoo]

Hi everyone.

I'm finishing with Varathane waterbased clearcoat in rattle cans. All was going..um..Ok. Lately I've noticed several pinholes have developed in the finish. I figured successive coats would fill them in but that doesn't seem to be happening.

1. What causes this;

air bubbles that burst as the finish dries? Little pockets of solvent( not shaking can enough?)

2. will they eventually fill in or should I sand them out? Should I spot fill them (there's dozens of them :-( )

thanx all

Stew

[AlGeeEater]

This is from ReRanch:

Pin holes can be caused by a number of factors. The most common are contamination of the wood by wax or silicon (Armor All used on the case or plastic parts can be a source of this type of contamination), temperature changes during the spraying /drying cycle and moisture in the wood. Wood contamination can be sanded out in most cases. Wiping with naphtha will also help in removing contamination. Temperature can also play a role in the formation of pinholes. If a guitar that has been in a cool environment  then sprayed (as might be the case if you are spraying in an unheated garage) and after spraying moved into a warm environment to dry, air bubbles may form as the wood warms and push their way through the lacquer leaving pinholes. The last frequent cause (and probably most common) is moisture in the wood. Water can get into the wood through washing stripper from the wood, wet sanding primer or sealer coats or not allowing a water based filler or water based dye enough time to dry. 

The solution? Sanding and wiping with naphtha should remove wood contamination and not subjecting the wood to major temperature changes during the spraying and drying process will prevent pin holes caused by bubbles (note that placing newly finished wood in the sun to dry is a guaranteed way to cause pin holes). Allowing the wood sufficient drying time after wetting will most likely eliminate moisture related pin holes. A sure way to prevent pin holes before spraying the lacquer coats is to seal the wood with a clear sand and sealer on translucent finishes and sand and sealer and/or a white pigmented shellac on opaque finishes. If you didn't seal the wood and now have pinholes you may be able to drop fill them with unthinned lacquer. The lacquer will over power the cause of the hole and allow subsequent sprayed coats to flow over the holes. After spraying about two coats the "bumps" from the filling can be sanded flat. Drop filling will work on sectional pinholes but if the holes are numerous and over a large area, starting over (this time either correcting the problem and/or sealing the wood before spraying the lacquer) may be the best solution.

Later,

Chris