Sap seeping through nitro finish... anything I can do?

[Dan Hehnke]

I recently took apart a guitar I made to give it a final polish since they lacquer is plenty set by now. I realized in the bright lights in my garage that the beetle kill pine body has splotches where some sappy parts seem to be seeping through. I had this board for a couple years, so I thought it was plenty dry and done seeping sap. Is it really seeping through, or is this something I can just polish out and it will go away? I'm really bummed to see this, as the finish was looking very good before, and was of course alot of work.

I can take a picture if needed, but basically it's dull, splotchy spots, mostly near knots and places you would expect sap to come out... I would have thought that nitro lacquer would be a plenty good barrier!

Thanks for any help!

[Clay Schaeffer]

Shellac is one of the few things used to seal in wood resins. It keeps knots from bleeding through paint.

[Dan Hehnke]

I was afraid someone would say that. I have sealed with shellac every time I did lacquer except this time.

[Clay Schaeffer]

You could try french polishing a coat or two of shellac on top of the lacquer. Old violin finishes are sometimes "brightened up" by F.P. shellac on top of the varnish. If well done the french polish will give a high shine just as lacquer does. I haven't done this over lacquer so it may or may not work, but may be worth a shot before resorting to stripping and refinishing.

[Mario Proulx]

Shellac is all that is needed under a nitro lacquer finish, so use that instead of vinyl sealer. Every time.

I would try sanding back a bit, rubbing-on a few coats of shellac(blond, de-waxed), then topping that with more lacquer. If that fails, you have no choice but to strip and start over9with shellac, then lacquer).

[Dan Hehnke]

Thanks for the tips! Unfortunately I've got barely any depth of clear coat left on top of the burst, so the most I could do is maybe scuff sand with 600 before trying shellac.

I did go at it just a bit with some coarse stewmac polishing compound on the drill mounted buffing pad, and the dull seepy part does seem to brighten up to normal, but I guess the question is, how long would that last? My thought right now is just to keep the guitar for now as my own (I was planning to sell it), and see if it happens again over time. Everyone needs a tele-shaped guitar anyway right?

If I do have to strip it, I'm tempted to just do my usual Tru-Oil finish next time around. Any experience with that over sappy wood? Would I still want to give it a coat of shellac first?

[Chris Reed]

For Tru Oil over sappy wood I'd definitely use shellac first. Tru Oil can be reluctant to dry on oily woods, I'd guess resin would be similar.

[David King]

I don't know how big these pockets or areas are but I'd worry that the sap will never set up under the finish and always be oozing or sinking. This wood might have been a good candidate for a bake in the oven prior to use to set the sap. If shellac will stop the problem then I'd wait and see what happens next. A refinish will probably seem more palatable in a month or two than it does right now.

[Dan Hehnke]

Thanks for the replies. I'm about to do a big move, so for now I think I'll just polish out and wait and see what happens.