Mortar for chimneys must be heat resistant.
Chimney mortar is a type of mortar that is intended to be used in chimneys. The process of applying mortar to a new chimney is known as pointing, while the repairs are known as repositioning. A related process, tuckpointing, involves using two contrasting colors of mortar to create the illusion of a very thin joint. Many hardware stores sell chimney mortar and can order special products.
Like other types of mortar, chimney mortar is an adhesive product that is intended to hold masonry pieces, such as bricks or stones, together. In addition to acting as an adhesive, chimney mortar must also be somewhat heat resistant so that it will not be damaged by high temperatures in the chimney. The mortar maintains the stability of the chimney and prevents water from penetrating the chimney and the surrounding structure. Chimney mortar is sold as a dry powder that must be mixed by the user as needed.
Remodeling is often recommended for brick and stone fireplaces. If the mortar decomposes, it can destabilize the chimney, creating a potentially dangerous situation. As mortar cracks and breaks, it also admits to water, which can cause water damage, promote mold growth, and allow bricks to crack under stress. Chimneys should be inspected regularly from top to bottom for signs of grout damage and repaired immediately when damage is identified.
If detected early, chimney mortar damage can be repaired by the homeowner, working over a day or weekend to carefully remove the old chimney mortar section by section and replace it with freshly mixed chimney mortar. It is best to do this when the chimney will not be used in the near future, allowing the mortar enough time to cure. Ideally, a month should pass, although specific products may have more specific recommendations.
If the mortar is badly damaged, the bricks are cracked or missing, or the chimney appears slanted or sagging, it is not safe to perform repositioning as a do-it-yourself project. A professional should be called in to determine whether or not the chimney can be salvaged and to do the job. It may be necessary to demolish and rebuild the chimney if it is badly damaged. People trying to fix unstable chimneys can risk causing the chimney to collapse, which can cause serious injury and/or property damage.