I have a stone fireplace and chimney in my house, about 50 years old. I will be replacing the roof soon, but I want to get the chimney in shape first.
I have estimates on the work needed, which includes new tuck-pointing and a cement cap, then a coating to minimize the porosity and make it as waterproof as possible.
One mason proposes using Siloxane Seal; the other says Thompson’s Water Seal is the best. I have no knowledge of either, and opinions would be welcome. Which should I use, or are they pretty much the same?
Also, one mason says “all mortar will have a bonding glue added.” Is this something that improves the mortar or is it part of all mortar anyway, and he’s just using it to hype the job?
A bonding agent is not part of all mortar and is sold separately and added during the mixing process. Adding a bonding agent assists the ability of the mortar to permanently bond to existing masonry.
On the water seal, do some research and select a product that allows the chimney to “breathe”. Many liquid sealants prevent water from permeating from the outside but also prevent water vapor from naturally escaping from the inside of masonry. Trapping vapor within the masonry can lead to spalling which can destroy masonry. There are products available that allow the masonry to release internal moisture while still preventing water from penetrating from the exterior.