MIMF

I love spalted wood and the idea occured to me of using spalted wood for the back and sides of an acoustic guitar. So I did a web search for spalted tonewood and came across this website: http://tonewood.rs/?cat=21. There is some beautifully spalted wood on there.

I'm wondering if there would be any structural concerns with using spalted tonewood. Would it be weaker and likely to fail?

Certainly there are structural concerns when using spalted wood. Wood is generally weakened by the fungus that causes spalting. It's suitability for building musical instruments must be based on the individual piece of wood, and somewhat on the skill of the person using it.

Spalting is another word for rot. But it usually involves wood that has not completely turned to mush. Some folks stabilize spalted wood with an infusion of CA glue or epoxy. I would not advise using it on your first few acoustics.

I've used spalted maple for the center of a 3 piece back, I would use it on an acoustic guitar, provided the spalting wasn't significantly softer. What I have the spalting is a little softer, but still harder than the spruce top. I did flood the surface with CA, but I was also filling the pores in the bloodwood on either side of the maple.

If I was using spalted wood, I would
1) laminate it in a side mold with a thin layer of spruce on the inside, for structural integrity
and
2) do a surface fill with epoxy before finishing, to harden the soft spots

The way I figure it, you need to make a few hundred mistakes before you really learn how to make a good guitar. This back and side choice might be one of those mistakes, but do what you want. You might as well get started making those mistakes, getting them over with and learning from them if you really want to do this.