The Basics of Chimney Repairs
Where to start with chimneys? Probably from the top: A chimney is not just an extended window. A chimney, shockingly, is a mechanism for engendering airflow to fuel combustion. Hot air from a fire in a fireplace ascends through the column of a chimney, creating a draft that drags more air into the fireplace, feeding the fire.
The outside of a chimney is generally made from brick, but the flue—the interior column—is normally made of clay tile. There are generally two types of flues: One for the fireplace, and one for the home’s central heating system. Lastly, there’s a unique cement crown on top of the chimney.
You should know that cracks in a brick or other type of masonry chimney are the first indications that your chimney is on the road to ruin. Hairline cracks in the summer can unexpectedly become large cracks by next spring. This can lead to water damages as the water begins to work its way down, sometimes between the outer brick and the flashing, sometimes farther inside, between the outer brick and the flue.
Left unbridled, all of these spells impending doom for roof systems and internal ceilings, insulation, wall studs, and even floors. Worse, cracks that continue from the flue to the exterior are one of the most common causes of a terrifying phenomenon called a chimney fire.
The good news is that fixing cracks in chimney brick, mortar, crown, and cap is a straightforward activity for a do-it-yourselfer and requires only a few simple tools and materials. You should endeavor to pick a warm, dry day for this project, as some of the materials need a few hours of curing time.
Chimney Repair Tools and Materials
- Joint raker, using for getting rid of brick mortar
- Tuckpointing tool for affixing and smoothing down brick mortar
- Pointing trowel
- Wire brush
- Putty knife
- Garden hose and water source
- High heat mortar and caulking gun
- Water-based silane/siloxane water repellent such as Prosoco Sure Klean
- Clean paintbrush
- Safety glasses
- Latex gloves
- Clean rags
Things to Repair in a Chimney
Bad Chimney Bricks
What’s That, You Say? You should know that even though the crown protects the bricks up top, the bricks on the flanks of the chimney can also be affected by water saturation.
What to do:
Replace Cracked Bricks
Severely damaged bricks should be totally gotten rid of and replaced. It is entirely possible to cautiously remove a single brick without damaging adjacent bricks.
- Slowly chip away mortar from between the bricks with a cold chisel or old flat-head screwdriver. Speed up the process and reach farther back by using a masonry-bit-equipped drill to bore holes into the mortar.
- Once the brick is slackened, pull it out by hand.
- Using your chisel, chip away residual mortar from the adjoining bricks so that they are smooth.
- Cover all four sides of the substitute brick (not including the front or back) using a trowel and brick mortar.
- Center the replacement brick in such a way that it the seams on all sides are of equal width.
- Get rid of any surplus mortar and smooth it down with the tuckpointing tool.
Repair Cracked Bricks on Your Chimney
High-heat mortar and a caulking gun can be used to repair individual chimney bricks that have a small crack or two;
- Clean out the crack with the edge of the putty knife or with the screwdriver.
- Sweep the crack clean with the wire brush.
- Squeeze the high-heat mortar into the crack as far as possible. Generally, the mortar will not extend very far unless it is a large crack.
- Wipe the mortar clean from the crack with your gloved finger. Then use a rag to clean the area around the crack.
- You may be able to close up cracks by brushing them with the silane/siloxane water repellent If they are very thin hairline cracks.
Bad Chimney Mortar
What’s That, You Say? Like any brick wall exposed to the elements, over time the mortar that holds it together will get damaged—cracks will form and chunks will fall out. When this happens, you’ll need to re-point it.
What Do I Do?
Repoint Your Chimney Brick Mortar
Mortar is the stuff that holds bricks together. New mortar is smooth and solid. But as time passes, the elements weaken the mortar, causing it to crumble. The mortar tends to always deteriorate first because mortar is softer than brick.
Repointing, or tuckpointing, is a common method that involves scraping out the crumbly mortar and replacing it with new mortar.
- Leave good mortar in place. Use your joint raker to scrape out loose, weak mortar.
- Gently tap out more difficult crumbly mortar with your hammer and chisel.
- Sweep out all remaining bits of mortar using your wire brush.
- With the garden hose, spray down the brick and let it sit for 30 minutes.
- Mix up the mortar until it has the texture of stiff peanut butter.
- Press the mortar into the open joints with your pointing trowel so that it corresponds with the look of the existing mortar.
- Using the tuckpointing tool, smooth down the joints.
Stuff is getting into the chimney flue
What’s That, you may say? The chimney flue is an important part of the chimney. You really don’t want anything getting inside the flue—not rain, not snow, not animals. Which is why a cap hangs over the opening, sheltering it from weather, and normally also has a screen to keep out critters.
What Do I Do?
Caulk Around the Flue and Crown
- One main way for water to come into your home and cause damage is between the flues and the crown. It is normal however, for a gap to form in this area as time passes. Water that enters this opening can move all of the ways down the flue.
- Clean out any debris such as mortar or moss with the wire brush. Fill up the caulking gun with high heat mortar, cut off the end of the nozzle, and pierce the interior seal. Stuff in enough caulking to fill but not exceed the area of the gap.
Chimney crown is cracked
What’s That, You Say? At the very top of the chimney, the bricks feature a horizontal surface that water and snow can accumulate on. However, If water seeps in, it can break down the masonry, sometimes even to the point of needing a full chimney rebuild. To prevent this, the chimney is covered with a coating of special mortar called a crown, which serves as a weather seal. If this crack or is damaged, it must be repaired.
What Do I Do?
Patch Large Crown Cracks
- A chimney crown is a type of rounded, sloping hat that forms the top-most section of your chimney. The purpose of a chimney crown is to cap the masonry section of the chimney and also, to prevent water from pooling on top.
- Due to the fact that water, snow, and ice remain longer on the largely horizontal areas, developing cracks can become a major problem faster than if the cracks were on the vertical sections of the chimney. Even with an advised 1:4 ratio slope on the crown, moisture will still linger on this area.
- Large cracks on the chimney crown that fall between the 1/8-inch and 1-inch range can be fixed with pre-mixed cement patch or mortar. Insert the repair mix into the crack with a squeeze bottle or force into the crack with a putty knife. Curing time normally ranges from four to six hours but may take a lengthier period of time for wider cracks.
Patch Hairline Cracks with Sealant
- Hairline or spider cracks are handled differently from large cracks since mineral particles in the patch or mortar are too large to fit in the hairline crack’s narrow space. The key is to use a water repellent that has high liquid inconsistency, as this will go into the hairline cracks. As an extra benefit, this particular product will seal up all other areas of the porous crown, stopping other hairline cracks from forming.
- Use the edge of the putty knife to scrape away any loose particles but be careful not to widen the crack. Apply the water repellent undiluted with a brush. For an average-sized chimney crown, one gallon should be adequate for two coats on.