Epoxy Bows Finished Board?

[Steve H Graham]

I've been fiddling around with a piece of 1/2"-thick walnut scrap, testing pore fillers. I did one side with spray shellac, and the other side has two coats of West epoxy on it.

Funny thing...after the second coat of epoxy dried, the board bowed so that it was concave on the epoxy side.

Curiosity drives me to ask...how do instrument makers cope with this? This is a thick, stiff piece of wood, and it bowed a good deal. If it were an acoustic guitar top, I'm sure it would be ruined.

Also, is there any possibility that applying epoxy on the other side will bring it back into line? I don't care about losing the scrap, but I was planning to try out my new card scrapers on it, and that will be difficult with a warped board.

[Tony Bilello]

There is a relatively inexpensive product made specifically for this purpose. It is called a paste wood grain filler. If you follow the directions it is fool proof -
works every time. I guess I am the only one that uses it.

[Howard Acheson]

That is what happens when you don't have a balanced finish on both sides. The epoxy is almost impervious to water vapor or moisture while the shellac will allow relatively more moisture through. This causes an unequal moisture content on the two surfaces.