Official Luthiers Forum!

Just started finishing my guitar with the crystalac line. I applied their sanding sealer and the finish bubbled up pretty bad on the sides. It didnt do this on the top or back so I am scratching my head trying to figure out what I did wrong. Does anyone have any ideas?

is ther a heat source near by? or are we speaking of small air bubles in the finish as apposed to finish blistering.

just tiny air bubbles. There was no heat, I did it at night outside, it was about 78 degrees.

Tiny air bubbles in the film are most often induced at application providing the wood was sealed with a sealer prior to applying the finish. Foam brushes are notorious for inducing air bubbles in vicious finishes. I never use foam brushes. Out side of that if you did not seal the wood prior to applying the finish then it is possible that gas from the wood has escaped into the film.

brushing most finishes require a retarder to allow the film to level before skiming over this also allows small air pockets to excape.

I do not know if you brushed on or not but that is the most common cause.

It was sealed with a pore filler and I did brush on with a good ox tail. Do you wipe on with a cloth or how do you do it now that you dont use foam brushes.

Thanks for your input Michael

I once had that happen on a hardwood floor I installed,where I bought the wood from a mill.. I was told the wood was not dried long enough .... just a thought ...maybe water still in the sides from bending ... Jody

Pore filler is not a wood sealer. Two different processes. Pore filler fills the pores level to the wood. A sealer like shellac or vinyl sealer is applied after the pores are filled to seal the fiber of the wood and the pore filler. Gases can still escape from the wood fiber. this very issue is one of the great reasons to seal prior to finishing.

The crystalac sand sealer is the sealer I used and that is what bubbled up. I havnt even tried to put the finish on yet. So you think shellac over the pore filler is the way to go instead of the sanding sealer?

First I don't use Crystalac. But if I did I would pad it much like I would apply Shellac or I would brush it, or I would spray it. But most important I would thin it to proper viscosity for the process i was applying it. Very few finishes come out of the can really ready to brush or spray. Even though the can may say suitable for. Most will require a retarder to brush or pad on and need thinned to sprayed.

OK even then it seams gas is the issue or air left by the brush. You did not have any pressure on the brush as you stroked did you? And I assume you did not back stroke. Never back stroke or add pressure to the brush you should just let the media flow out the back of the brush. And never go back over a coated area within a single session. These are both ways to induce air into the film.

Thanks Michael Ill give it a go again with your suggestions

On a side note, since we are talking about using a brush, here is what I use.

It's a foam brush with paper towel around it. It eliminates bubble issues that are frequent with brushes.

Works a charme, and it also greatly reduces runout issues I had when using the brush without the paper towel around it.

_________________
Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)