Question: I have a masonry wood-burning fireplace with a wood-burning insert that I haven't used in a number of years due to allergies. Several years ago the clean out door rusted off its hinges and I bricked up the hole rather than replace the door. In the winter I noticed a draft coming from the ash dump hole and filled in the ash pit with sand. This summer I noticed an strong odor of rotting vegetation coming from the ash dump hole. I pulled out the insert and right now am cleaning out all of the sand which I see has gotten wet and moldy. It is the source of the smell. I filled in a couple of very small cracks in the chimney masonry outside which may have let in the rain. What can I do next? I probably need to fill in the ash pit with some type of insulation to prevent the draft, but what should I use? Also, I plan on replacing the insert with gas logs. Answer: Masonry is very porous, so it is difficult to trace and remove the source of these smells. Sounds like you are on the right track, but here are some other suggestions: 1. Put a cap on the chimney. This will eliminate moisture, which soaks deep into the fireplace and foundation. 2. Make certain that the crown (top) of the fireplace chimney is tight and waterproof. 3. Check and seal flashing between the fireplace and the home and roof. 4. Seal outside of fireplace with clear masonry sealing compound. 5. Clean chimney and fire box. 6. Use fireplace deodorant - available at fireplace stores. 7. Seal the ash door opening...a piece of sheet metal sealed with silicone should do if you install your gas logs on top of this.