Fireplaces are a pleasant addition to home and can provide an enjoyable source of warmth in the wintertime. However, like all areas of a home, fireplaces do need the occasional maintenance in order to operate properly and safely. Since fireplaces are used to contain flames and toxic combustion byproducts, their regular maintenance is crucial for the safety of a home’s occupants.
Most wood burning fireplaces are composed of three components; the chimney / damper, the firebox (which can be composed of metal, masonry, or modular), and a fire brick liner. This last component is critical in absorbing heat and protecting the firebox from the damaging effects of the fire. Fire brick liners also help to keep a steady warm temperature produced from the fire and protect the wall behind the fireplace. While fire bricks and fire mortar are relatively durable, they can deteriorate over time and crack which can allow heat and gasses to become a hazard.
Firebricks are a blocks of refractory materials and unlike ordinary masonry bricks, can withstand temperatures up to 1,800 degrees Fahrenheit, whereas ordinary bricks begin to deteriorate at around 1,200 degrees Fahrenheit. This elevated durability is in part due to the chemical makeup, which is mostly silica and alumina. This makes firebricks more dense than ordinary bricks, helping them to withstand the extreme heat inside a fireplace.
Since these bricks are subject to extreme temperature changes, they must be held in place with an equally durable material such as fire cement. While most types of mortar or cement fails at such extreme temperatures, using a flexible and durable material such as fire cement is necessary as this cement maintains their structural integrity during heavily fluctuating temperatures.
To repair damaged or cracked fire brick in a fireplace, first clean the surface of the area to remove any soot, grit, or dust and allow the brick to dry. Using a trowel, apply fire cement to the area and wipe off any excess cement from the brick. If there are broken pieces of the brick, place cement towards the corner of the damaged section and push the pieces back together with the cement holding them in place. Repair any cracks by placing cement into the crack and removing any excess from the surrounding bricks. Apply heat at a gradually increasing temperature to the bricks for three to four hours, allowing them to cool afterwards. Repeat this process for cracks if there are any present afterwards.