Repair Chimney and Firebox Cracks and Leaks

Repair Cracked Mortar

Masonry chimneys and masonry fireplaces are constructed using bricks and fireclay mortar. The bricks and mortar are designed in such a manner so that they do not get damaged under extreme temperatures. However, with enough time and usage, like anything else, regular wear and tear gets the best of them. The mortar, brick or panels can crumble or crack. Cracks are a serious fire hazard and if you know you have cracking, you should stop using your fireplace until they are repaired. A lot of times, the cracks are further up the chimney and not visible, which is why it is so important to get your chimney inspected annually by a professional chimney sweep. Your chimney sweep will examine the entire chimney and suggest the best course of action that you can be take given your unique situation.

For those who are interested, here are steps your sweep will follow to repair cracks:

Step 1: The first step would involve locating the damage that has occurred in the chimney mortar by extensively inspecting the chimney from inside and outside the home. When the mortar is cracked it will break and crumble to the touch.

Step 2: Your sweep will remove the chimney mortar that has been damaged first. He/she will need a protective mask and glasses to avoid inhaling chimney dirt or mortar dust and to protect their eyes. Mostly, a wire brush is used to remove the damaged mortar from the bricks to which it is attached. If the damage is really bad, the bricks can literally be picked up off the chimney. Once all debris is removed, you will have a smooth surface to work with.

Step 3: The mortar should be replaced in its entirety and not in bits and pieces. This is to avoid making your chimney unstable. The mortar needs to be specifically for fireplaces and chimneys such as Quikrete or Rutland’s furnace cement. Mix it in a bucket as per the instructions given on the label. After preparation of the mixture it needs to be poured in the chimney to fill as much cracking as possible. If you are completely laying new bricks, you can use a trowel and spackle on each layer of brick and mortar. The process needs to be continued until all the different areas that have been identified initially are repaired.

Step 4: The last step would be to give the finishing touch. Since the job of filling the cracks with mortar is quite messy it might be possible that chimney mortar gets poured in the areas where there are no cracks. In such a case it is easy to remove the excess mortar by placing a damp towel on the excess area and removing the excess mortar. Also the damp towel can be used to smooth out the mortar that has been applied in the affected areas. Once the chimney mortar sets completely, for a nice appearance the excess debris can be brushed away with a wire brush.

Your professional chimney sweep will know all the precautions and safety codes that need to be followed to repair mortar cracks safely. It is their job to make sure that the job is done correctly to make your chimney safe and long lasting.

Repair Cracks in Chimney Liner

A crack in the chimney liner may be caused by several reasons such as improper construction of the chimney that causes thermal expansion, expansion/contraction due to leaking water and ice, or a natural disaster such as an earthquake or tornado. Also, after enough time, gravity leaning down on the chimney or settlement of the house can even cause the chimney to crack.

In order for your chimney liner to work efficiently and correctly, it should be free from cracks and gaps. Otherwise, gases going up through the chimney will not be able to rise and go out.  A backdraft from the cracks can reverse the flow of air and bring harmful air into your living area.   

Proper annual inspections and regular maintenance by a professional sweep are the keys to detecting chimney cracks. Without a regular cleaning, you may continue to use your fireplace until you suddenly notice seeping water through the sides of the chimney, or dark black creosote stains carried to the chimney surface on your roof.  These are telltale signs of cracks in the flue liner.  Unfortunately, a cracked flue liner of the chimney isn’t an uncommon problem.  Many masonry fireplaces are built with the clay liners that experience general wear and tear and with enough time and intense heat, they will crack. Cracks and gaps allow poisonous gases to escape into your home and also allow creosote to escape into the chimney and create a fire risk.  If you have a crack in your flue liner, your professional sweep will recommend replacing the entire liner.

Repair Water Damage from cracks in Chimney

If your chimney has already had extensive water damage from cracks, it should be repaired before any waterproofing agents are applied.  You may notice water damage on your roof, or interior ceiling or walls near or above your fireplace.  The chimney’s exterior most likely will have to be cleaned and any damaged interior materials will need to be replaced before the application of a waterproofing agent. Paint, or any non-vapor permeable water sealer, should never be used as a waterproofing agent because it will trap moisture inside your chimney causing internal chimney leaks, accelerating deterioration from within.  After repairing cracks based on the advice given earlier, you will need an all-purpose, heavy-duty water-based repellent to prevent leaks from coming back.  Again, this is a job better left to a professional chimney sweep who can do a full inspection and assessment of the damage the water has caused and recommend the proper technique to repair your chimney so that it is workable again.  Water damage is one of the most destructive forces that can occur and often requires replacement of existing cracked or leaking parts to make your chimney safely functional again.

Chimney Crown Crack Repair

Your chimney crown can crack from any natural disaster, and also from regular wear and tear from rain and wind, especially if you live in a part of the country that freezes and thaws often. Depending on the severity of damage to your crown, it will either need to be totally replaced or repaired. If the cracks aren't too severe to warrant total replacement (which would be best performed by your professional chimney sweep), the best way to perform a chimney crown repair is to use an elastomeric product that will remain flexible over time. Before you opt to do this work yourself, you should have the chimney crown professionally assessed during your annual cleaning. Your sweep can repair the crack or recommend that you can do it yourself.

If you opt to do your own work, companies such as ChimneyRx or ChimneySaver sell a number of brush-on crown repair products that you can brush on over the entire crown surface and they will fill in the cracks and prevent new ones from forming. They protect your crown from the elements as well as fill in the existing cracks with their waterproofing agent.

The first step is to take a wire brush to the entire surface of the crown and remove the loose debris surrounding the crack.

Next, line the edges of your flue and crown with tape to prevent the product from getting on the roof, much like you would line the crown molding before painting the interior of your house. This will give you a clean edge after you are finished.

If there are any cracks on the crown, use a high quality, exterior silicone or acrylic caulk to fill in any cracks. Allow this to set for 10 or 15 minutes. Don't worry if it's not totally dried before moving on to the next step as the caulk will cure beneath the surface.

Next, apply at least two coats of your crown repair and allow it to set for the recommended time on the packaging in between coats. You don’t want to let it set for too long because it will be too hard to smooth out evenly with your brush. You can remove the tape once it is fully set and your repaired chimney crown is now safe from cracking and fire hazards.

Again, the do-it-yourself approach should only be done if it is advised safe by your professional chimney sweep. They will also be able to assess the work you have done during their annual inspection, prior to you relighting a new fire in your chimney to make sure airflow is correct and safe. 

Repair Chimney Spalling Stucco or Concrete Cracks

To fix cracked or unbonded stucco the best way is to tear it off. Completely replacing the stucco will ensure it is stable enough to support the weight of the chimney and it also gives you the opportunity to look behind the stucco at the exterior of your liner to make sure there is no further cracking or water damage deeper in your chimney. Hearth cracks, fireplace side cracks, and external chimney damage all present risks of sparks or smoke entering the building cavities and starting a fire as well as flue gas leak risk. Call your chimney sweep to check for evidence of movement of your fireplace or chimney. Flue gas leaks or sparks into the building interior, a fire, or potentially fatal carbon monoxide hazard are not worth the risk and professional will let you know all your options. If you have extensive internal water damage or cracking, you may need to also replace the liner or the entire chimney.

However, if it is determined that you simply have some cracked stucco, it can be removed and replaced. Step one, is to remove the old stucco where the cracking is present, which can be done with a hammer, chisel, and pry bar. You want to make sure you remove all loose pieces completely, to make the new wall structurally safe again. Once you remove the loose pieces, hose down the surface and use a wire brush to remove all dust. The new stucco will not adhere properly if there are dust particles blocking it. You are now ready to mix the new stucco and apply it to your wall. Analysis of the historic stucco will provide useful information on its primary ingredients and their proportions, and will help to ensure that the new replacement stucco will duplicate the old in strength, composition, color and texture as closely as possible. The instructions on the mixture you purchase will tell you how to prepare your stucco and it can be reapplied with a trowel and smoothed out with a finishing brush. You should apply two coats and the first coat should be scratched with a comb to provide a key to hold the second coat. The final coat can be smoothed with a wood float to match the texture of the original wall. Allow it to completely dry before painting or whitewashing if you choose to cover the surface.

Cracked Chimney Pot Repair

Your chimney pot is made of either clay or terracotta. Many people prefer to use clay because of its appealing color but there are many other reasons to use a clay pot. Clay pots are fire resistant, dust resistant, and are not affected by any type of corrosive chemicals. However, they are not particularly strong and can crack frequently. Before starting the work of fixing a cracked chimney pot, professional sweeps would like to take a look at your chimney pot to assess the level of damage. They may recommend fixing your existing chimney pot easily so that you don’t need a costly replacement, replacing it entirely, or repointing the mortar at the base of the pot and then repairing it. This is all dependent on the level of destruction to your existing chimney pot. If it is determined that you can fix the existing chimney pot, here are the steps that you or your chimney sweep will follow.

Wear gloves and a mask, and clean all the debris on the chimney pot by using a line brush or wet scrub brush. Then rinse the pot with slightly warm water and wait for an hour to let the pot dry.

Apply silicone or glue next, to fill the cracks in the chimney pot. Make sure to apply glue or silicone delicately so that further damage of chimney pot and its design is prevented. You can also place clamps to hold the pieces of pot together until the adhesive has been dried. After allowing the glue to dry completely, remove the excess adhesive by scraping it off with a blade. You can add a final touch by sanding and/or painting the pot if you desire.