Some masons “work too fast” and don’t think it’s actually important to seal the joints.

The reasons there are bad mortar joints or cracks in chimneys are numerous, including:

In short, it’s probably best to remove the old tiles completely (getting rid of creosote on the outside of the tiles as well) and replace the liner with a new insulated stainless steel liner. Frankly, even if servicemen remove as much creosote as possible, the cleaning does not yield as much safety you’d hope for. It is probably best to consider unsafe any chimney that has had 3 rd degree creosote in it, especially if there has been a chimney fire. A house fire becomes a much greater possibility. This is a very serious problem because in a chimney fire this creosote ignites as well and becomes a slow-burning creosote fire not contained inside of a liner. The problem with having openings in the system is that liquid creosote can and does go through the joints and/or cracks and accumulates outside of the flue tile. I might lose one or two $10 bets, but that’s about all. In fact, if I were to blindly bet ten people $10 that their chimneys have poorly sealed mortar joints and then we investigated with a closed circuit chimney inspection camera, I stand a good chance of making $100.

In tile-lined chimneys, it’s the exceptional chimney that has good mortar joints. Now for the case for not removing 3 rd degree creosote from tile chimney liners. In part 2, we explained how to remove creosote. In part 1 of this series, we explained the three stages of creosote buildup. Why You Should Not Remove 3rd Degree Creosote from Tile Liners

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