How to Fix a Fireplace’s Loose Mortar?

Fixing a fireplace’s loose mortar can be a quick and inexpensive way to improve your home’s appearance while keeping your family safe. Loose mortar can be the result of a variety of factors, including poor maintenance or improper installation. It can also be a sign of a more serious problem, such as a crack in the bricks or a missing fire panel. 

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A cracked fire brick is a major safety concern and should be repaired before using the fireplace again. It’s also necessary to inspect the smoke chamber, a part of the fireplace that moves soot, creosote, and other dangerous gases away from your home and up to the chimney. If you notice a crack in the fire chamber, call a professional chimney repairman or mason as soon as possible. 

Choosing the Right Caulk for Your Fireplace

Refractory heat-resistant caulk is ideal for repairing and sealing masonry and fire bricks. It’s specially formulated to resist expansion and contraction caused by the high temperatures of a wood fire, which can lead to bricks and mortar breaking apart. 

The best type of refractory caulk to use is one that is approved by the National Fire Protection Association (NFPA). Some of the most common brands include Rutland Dry Mix 211, AW Perkins 245, and Heat Stop II. 

Choosing the Right Tools for Fire Brick Mortar Repair

Before beginning any refractory mortar repair, remove the old mortar with a scoring tool. Scrape out any loose mortar on both sides of each joint, 1/2” to 3/4” deep. Repeat this step as necessary until the deteriorated mortar is removed. Once all of the joints are free of deteriorated mortar, fill them with refractory mortar. Let the filled joints set for about 30 minutes before tooling them. 

Apply the refractory mortar to each brick face with a tuck-point trowel, and smooth the surface with the edge of the trowel for a uniform appearance. You can then use a brush to wipe up any excess mortar from the bricks. Once the mortar is dry, it will have a light grey appearance that contrasts with the black soot on the fire bricks. 

Next, spray the filled mortar joints with water to slow down their evaporation. Mist them a few times a day for a week to help the new mortar cure harder. If your area is low on humidity or too hot, tape plastic sheeting over the repaired mortar to keep it from drying out. 

Tuck-Pointing Your Fireplace’s Loose Mortar

If you’re dealing with a large patch of deteriorated mortar, the tuck-pointing method is your best bet for repairing it. To do this, you’ll need a scoring tool, a brick trowel, and a narrow enough-to-fit-in-the-joints tuck-pointing trowel. You can also use a pointing tool for this job, but it will be much easier to do if you have a tuck-point trowel. 

Depending on your experience, you can choose to replace all of the mortar around your fireplace’s fire bricks. To do this, you will need a tuck-pointing trowel and refractory mortar that meets NFPA 211 specifications.