Q. What happens to stained wood in a bathroom which has been exposed to dampness? Also, what is the difference between varnish and shellac? Ann Hattes Danvers, Mass.
A. Exposed stained wood in a bathroom is liable to mildew, which is often difficult to remove without periodic bleaching.
Wood is very porous; thus, mildew tends to lodge in the pores, making it tough to remove.
Even a coat of rather unnoticeable flat varnish applied to the stained wood will help seal and smooth the surface against the incursion of mildew. But even then, mildew could occur but its control would be much easier than on wood which has merely been stained.
Now, about the difference between varnish and shellac:
Varnish is a synthetic finish made from petroleum byproducts which usually is thinned with turpentine or paint thinner. It may yellow slightly with age but it is less apt to discolor to the extent that shellac will.
Shellac, which is thinned with alcohol, is in its clear state slightly orange in color. It is made from the secretion of an insect (Laciffer lacca) found in India and Indonesia. These insects live on the twigs of certain native trees.
The resin is collected, dried , and purified to make various grades of shellac.