Chimneys are often an appreciated feature of home decoration, so it’s not surprising that the mortar or bricks gets damaged or deteriorated should receive prompt attention and careful repair. Use a type of special mortar for repairs in the combustion chamber; elsewhere you can use some types of standard mortar, but for better repairs, use additives.

Refractory mortar

For the repair of the combustion chamber, the inner chamber where the fire burns, use a special type of mortar resistant to extremes of heat and temperature cycling. Known as refractory mortar, it uses binders as calcium aluminate or sodium silicate that tolerates high temperatures, rather than Portland cement. The refractory mortar is available for hydraulically placement and air drying, or premixed. The hydraulic setting of refractory mortar is resistant to acids and soluble in water once cured; it is suitable for indoor and outdoor applications. The precast refractory mortar which dries quickly is water soluble, can be washed, so it is easy to clean, but is only suitable for indoor use.

Standard mortars

Standard mortars are made using Portland cement, hydrated lime and sand combined with water to obtain the right consistency. Depending on the nature of the repair, the standard mortar may be adequate or modified by adding a small amount of additives to improve certain properties. The type N mortar is the best for general-purpose and is recommended for most projects. The mortar type O, also known as indication mortar has features that make it better suited for non-structural repair; mortar units generally in situations of higher grade. The K type mortar is used in situations where historic preservation load resistance is not important; it has a porous nature that helps prolong the integrity of the oldest blocks.

Additives

A number of ingredients can be added to the mortar to create special mortars for certain circumstances. Many repair mortars are created using an additive polymer such as polyvinyl acetate, dichloride and acrylic or modified acrylic adhesives or act as water-reducing agents, increase strength and permeability limit. The accelerators can be added to the mortar to shorten setting time, quality especially useful in cold weather. Retardants are added to extend the working time of the mortar and slow the hydration of cement during hot weather. Color pigments are also commonly added to repair mortars and replacement thereof should match the existing mortar.

Making repairs with mortar

To perform the repair mortar, you may have to clean the inside of the home to identify any defective seals. Use a chimney cleaner as indicated. Remove mortar or damaged bricks with mortar rake, a chisel, a hammer and a stiff brush. Moisten the surface of the bricks to join the mortar. Prepare mortar and apply it in the joints in layers of 1/4 inch (0.6 cm), allowing it to cure for about 30 minutes between each coat. Once the brick surface is achieved use beam tool to match the existing cement mortar. Clean the face of the bricks with stiff brush or a damp sponge.