Question: We purchased gas logs and put them in our existing fire place. We have them partially vented. Our problem is black soot that is building up on the ceramic logs. What is the cause? I know some build up is expected but not after such little use. I would be grateful for any help you could offer. Answer: Could be a number of things: 1. Some logs have an air shutter adjustment that could be set wrong 2. LP gas can cause a lot more soot than natural gas. 3. Logs and/or sand, etc could be placed wrong. 4. Try opening your damper 100% - keeping it partially closed could create soot in the house and on the logs...depends on chimney draft and log settings. 5. Could be simply normal for the log set you purchased.