Crack Chimney Repair

A chimney is relied upon to channel smoke up and out, but when the outside or inside walls of a chimney crack, you may have serious problems. After 25 or 30 years of exposure, Mortar Joints between stone or bricks can begin to flake, washout, or crack – and that is a problem!

What causes these cracks? Usually, the problem is the “freeze-thaw” process, especially in colder climates. Moisture can also make its way into the masonry, the integrity of it, and any attached object made of metal, like a lightning rod or satellite dish compromising

crumbling brick chimney
crumbling chimney

The risk of damage to your chimney increases if you live in an antebellum home (a home of historic age). Before the use of natural gas or oil for heat, coal was used. Chimneys built to accommodate the high heat of burning coal that powered boilers are oversized and are not capable of handling the temperatures of oil or natural gas. This kind of chimney can lead to the risk of condensation and its corresponding damage. The top area of most interior walls of the chimney are the most frequently vulnerable, as well as being the most difficult to notice. Unfortunately, the neglect and lack of inspections often lead to a need for major and costly repairs.

Your home’s location may also increase a chimney’s risk of damage. For example, homes in areas prone to earthquakes or shifting soil bases frequently sustain chimney damage. Because chimneys are essentially rigid, they don’t move with ground shifts, like many homes are able to do (i.e., wood-framed homes). The danger is that damaged chimneys can permit toxic gases, such as carbon monoxide, to leak into a home creating serious health issues.

Always be sure to check your chimney at least once every two years for damage. You’ll want to search around your home for missing or loose flashing — the metal sheeting that keeps the place where the roof and chimney meet watertight — and any signs of damage to the masonry, especially if there is any cracking. Take note, any serious problems need the attention of a professional. As well, many communities require a permit for chimney work.

If you find a problem when you inspect your chimney, always call a professional to determine the severity of your chimney issue.

Chimney Problems or Questions? 

Chimney Crack Repair Tools and Materials

Before beginning any chimney repairs, you (or someone you have hired) will need to clear away any debris (such as bird nests) in the chimney. To get rid of creosote (the tar-like material that the burning of wood creates), you will need a chimney brush (you can rent one that corresponds to your chimney flue’s inside diameter). Make certain that you seal the fireplace opening before you start repairing the chimney to keep from creating a mess that is almost impossible to clean up. As is true in most serious home repairs, it is always best to call a professional so that the job is done correctly.

You will also need to have a safe and sturdy footing on your roof as you clean the chimney (note: this is especially important as it is a serious safety issue). Once you have a secure position, insert the brush and move it up and down with enough pressure to remove soot without damaging the structure.

A true professional who has worked with chimneys is familiar with tuckpointing, which is the replacement of fresh mortar for failed mortar joints. When performed correctly, with a mortar-raking tool, the process will clean the damaged mortar. When this cleaning is not enough, a masonry chisel and hammer may be required to finish the task.

Sometimes it is necessary to use a mortar hawk to get mortar into tough places, such as into horizontal joints. When it comes to vertical joints, you may want to use a joint filler to spread the initial layer. On occasions, it may be useful to mix a concrete fortifier (or pigment) in the mortar so that the end result will match the rest of the chimney.

Once you have gathered your tools and materials, you can read on to learn more about repairing stone or brick chimney cracks.

Repairing Stone Chimney Cracks

If caught soon enough, some cracks may be easy enough to repair yourself. When you choose to do this, clean the area and then simply fill in the crack with caulk or some sort of concrete bonding material. Follow the finishing steps outlined by whichever material you choose, but it’s usually a standard procedure of smoothing the bonding materials with a flat-edged tool, like a putty knife. If the area is uneven after drying, you may want to sand the area to help it to blend in with the area around it. However, as in all DIY repairs, be sure that you are not covering a more serious problem that will surface later – often at great cost.

If the mortar around the stone has begun to crumble, you will need to remove it with a small hammer and chisel (be careful if you choose to do this yourself). You can then take out portions in a square shape. You will need to try to go at least a half-inch (1.25 cm) deep. Once that is done, you can clean and dry the area so that it is moist, but not wet. At this point, the area is ready for mortar.

brick wall

When you mix your weather-resistant mortar, aim for the consistency of peanut butter. Again, you can use a mortar hawk (or a pointing trowel) to spread mortar into the damp excavated areas. The mortar should dry to a stable consistency, but you should still be able to leave a mark with a pressed thumb. So many of the mortar mixes available for purchase simply need water, so follow the directions exactly and the consistency should be OK. You should always start with vertical joints and then move on to the horizontal joints, making sure to clear away any excess mortar along the way. You will need to repeat this process wherever you find damage. To ensure the quality of your repairs, let the mortar set properly by keeping it moist for the first 3 or 4 days while it is setting.

If your chimney is made of brick rather than stone, continue to read on.

Repairing Brick Chimney Cracks

Maybe you have noticed some dampness in your attic. One cause might be a leak in the chimney crown. If there are hairline cracks in your chimney, it’s likely that water is entering during severe weather. These cracks can occur even during new construction, due to shrinkage.

Strong winds can also cause cracks in the mortar. It is not uncommon for mortar to take as long as a few months to reach its full strength. During this curing process, strong winds can create tension. This is why modern builders will frequently insert steel rods into their chimneys as they are building.

A solution for repairing leaks in the bricks that are a part of your chimney system is to apply a clear silane-siloxane water repellent to the bricks. This kind of water repellent allows the water vapor to escape but keeps liquid from entering the brick.

If the problem lies with the mortar instead of the bricks, then just go back to our prior instructions on mortar repair and follow those procedures. These are versatile procedures for many chimney types, be it stone, brick, or concrete.

As a follow-up note, always use a herbicide to kill plants before removing them from a chimney. While these plants are alive, they often have their roots or vines secure in the mortar, meaning that if you try pulling them out, you could cause damage. It is rather recommended that you cut them off at the ground level and then use a putty knife to remove the dead plant.

By keeping your chimney in a good state of repair you will allow yourself to enjoy many safe hours of fireplace use. Use caution when implementing these tips and suggestions and seriously consider contracting a highly trained and experienced professional to do the job instead.

Professional Grade Solutions For Chimney Problems


Most chimneys will need added support at some point to stabilize and straighten their structure. It is recommended that this be done with an installation of helical piers. Our network of foundation specialists uses helical piers from Earth Contact Products.

Helical piers look almost like a giant screw. They can be installed with little interruption to your yard and home, and they will be able to support the load of your chimney. The job can be done in any type of weather and is usually completed in a very short time.

When you notice your chimney leaning, tilting, cracking, or separating from your home, please do not ignore the problem. When you have a professional look at your chimney problem, you might also be advised that other foundation problems exist and you could save you money in the long run by having all your issues addressed at the same time.

Use My Foundation Repairs to find an expert in your area for all of your foundation repair needs. You can get a free inspection and estimate, too!