We have a powder bath that often has a humid smell similar to damp hay. I have checked for leaks and bleached the toilet and sink drain but the smell persists. With a UV light I can see what looks to be a moist area on the ceiling which would indicate a leak from the tub above. By hand, I can't tell whether the ceiling is damp, or just cold. I do know that the putty around the drain had dried out two years ago which resulted in ceiling discoloration about four feet away in another room. I am beginning to wonder if the leak also traveled along the bottom of the tub or a joist.
Can I use a woodworking moisture meter to test drywall?
If so, can anyone recommend a model that you are also happy with in the shop?
Todd