A disadvantage of hot glue is that it does not fill in cavities. Normally this is good, you are forced to have a good fit, the glue sticks best when the two pieces of wood are in contact with each other. There is a recurring problem; when you glue the bridge back on an old guitar, the cover is always more or less damaged under the bridge. It may be that the bridge has already been glued back and the cover was damaged when the bridge came off, or that wood fibers are pulled off if the glue is good. If the cover is of poor quality with inclined longitudinal fibers (run-out), it is easy for the spatula used to loosen the bridge to follow the fibers down into the cover. Damage and pits need to be filled in with new wood or with glue that fills the cavities well.

I have a bag of Lycopodium spores that can be used to fill cracks in spruce. The fine yellowish spores do not turn dark when wet or glued, as is always the case with wood dust. It occurred to me that I could use Lycopodium to give hot glue bulk that can fill in cavities better. I did a test by gluing two pieces of spruce with hot glue and two other pieces with hot glue with Lycopodium powder added. Both joints were very strong, I could barely separate either of the two glued pieces of spruce.

To see if I could get more bulk in the glue with Lycopodium, I made small thumbnail-sized drops of glue and let them dry overnight. The glue drop with Lycopodium was 0,5 mm thicker than the one with just hot skin glue when they dried. Fresh hot skin glue with Lycopodium also has a thicker and less runny consistency. An advantage when, for example, gluing back a bottom. The consistency is comparable to original TiteBond.

I will use this trick from now on when I glue stables to a damaged surface to effectively fill in any small damage.