Chimney Brick Spalling [What it is & What to Do about it]


A chimney in your house offers a means of architectural ventilation, isolating the hot and toxic exhaust gases or any smoke generated from living areas. 

While it’s beneficial to have a chimney in the house, proper maintenance is important to make sure it functions efficiently.    

If your house has a chimney, there could be several things that impact the condition of the chimney mortar and bricks. One such common issue with chimneys is brick spalling. 

Here’s your guide on what it is, why it happens, and what you can do about it.


What Is Spalling & What Causes It?

Chimney brick spalling refers to the condition of crumbling or dislodged chimney bricks. One of the earliest signs of chimney brick spalling is damage to the chimney’s exterior surface.  

Chimney brick spalling can result from several reasons. 

Most commonly, it occurs due to moisture penetration in the mortar and bricks. When the moisture contained in the masonry expands and then contracts (freeze/thaw cycles), it leads to a breakdown that causes cracking and crumbling.

If this is left unchecked, it damages the entire chimney structure. 

Your chimney could be suffering from moisture issues due to a number of reasons such as:

  1. Salvaged bricks were used during construction of the chimney, making the structure more prone to any moisture damage.   
  2. You live in a climate region where water is more prone to freeze and thaw. In wet and cold climates, the weather results in the mortar swelling and releasing. This puts pressure on the bricks and results in brick spalling. 
  3. The use of sandblasters and pressure washers have destroyed the exterior of the bricks, making them more prone to water damage. While these are typically meant to clean the bricks, excess pressure can damage chimney bricks and result in chimney brick spalling.  
  4. Your rooftop’s layout is such that excess water inundates the chimney, accelerating the damage to the masonry and leading to spalling. Damage to the masonry in such conditions results from bricks and mortar staying wet for excessive amounts of time. 
  5. There are cracks in the chimney crown because of its low durability, which leads to moisture saturation of the mortar and bricks.

Cheap Materials

Another major reason for chimney brick spalling is the use of cheap mortar and bricks. 

Inferior materials tend to have shorter lifespans and suffer from damage much faster than high-quality bricks. 

When the compression rate used to make mortar under heat isn’t accurate, brick spalling tends to occur. Mortar is meant to absorb any expansion of the chimney bricks under stressful circumstances like freezing and thawing. 

When the mortar used isn’t of good quality, it can’t absorb moisture from freezing and thawing. This results in the bricks being squeezed instead of protecting them.    

House Structure

How your home is structured on the outside can also accelerate chimney brick spalling. 

If the exterior architectural structure isn’t strong or exposes the bricks to weather conditions, the mortar and bricks will get strained. 

Even the state of bricks used on the exterior of your home can lead to chimney brick spalling because different structures of your home depend on each other. 

A weakness in one will inadvertently lead to problems in another. Poorly constructed chimneys also prevent the proper functioning of bricks and mortar, which can lead to brick spalling.

creosote sweep

Age of Your Chimney

Age is another factor that can lead to chimney brick spalling. 

Chimney bricks, as well as the mortar connecting them, can decay as a result of old age and cause spalling. 

Experiencing a lightning strike can also lead to brick spalling within the structure of your chimney. 

Even regular settling of houses over time can lead to chimney bricks and mortar forming cracks, especially in situations where the building of the chimney was done wrong.

What problems can Arise From Chimney Brick Spalling?

Worsening of the chimney condition 

You may think that ignoring any crumbling bricks or mortar will save you money, but in reality, you’re only going to end up spending more money. 

This is because ignoring the condition won’t make it better or even help to maintain it in the same condition. 

It’ll only get worse. 

Any cracks in the bricks or mortar will result in moisture entering much quicker. The trapped moisture will undergo cycles of freezing and thawing, which just puts more stress on the brickwork. 

This will just worsen the brick spalling. 

The area is also more likely to form mold due to water retention. Not only is mold an unpleasant sight, but it also poses a grave health risk. 

A higher likelihood of chimney fires 

If you have a weak chimney structure, there’s a higher build-up of creosote or the black tar from smoke on the sides of the chimney flue. 

When this accumulates into thick layers, any tiny spark from the fireplace can reach this flammable substance and lead to a chimney fire

This is why it’s crucial to keep an eye on the condition of the bricks that form your chimney. Spalling bricks and crumbling masonry increases the likelihood that sparks will reach the wooden sections of your house and result in a fire.

The collapse of your chimney 

If you don’t check the brick spalling in time and attend to it, it can result in a compromised chimney structure. 

Spalled bricks affect the strength of other bricks around them and can result in a domino effect. Even other structures like drywall, framework, and boards can get damaged as a result of brick spalling. 

Repairing brick spalling and correcting cracked mortar is always going to be cheaper for you than having to rebuild the full chimney. 

This is why it makes sense to closely monitor the state of your chimney and conduct the needed repairs in time to avoid a collapse of your chimney.  

While it may seem like you’re saving money in the short term by avoiding repairs on your chimney, the above problems clearly show that doing this has dangerous consequences, which can cost you a lot of money in the long run. 

Preventing Chimney Brick Spalling

The first step to take to protect your chimney from brick spalling is to take measures that prevent it from happening. 

To do this, it’s necessary to apply a waterproof sealant so that water doesn’t seep into the chimney bricks. 

Choosing a breathable waterproof sealant is very important, or else it can result in moisture getting trapped between the bricks and coating, which will actually worsen the condition. 

This will need to be done every 3-5 years to keep your chimney protected. Prior to applying a breathable waterproof sealant, you’ll need to have an expert inspect your chimney structure, flue, and crown, so that you can get an understanding of how much damage has taken place. 

Annual inspections of your chimney by an expert will also help you detect any issues and prevent dangers from brick spalling. 

These are some signs that you should watch out for:

  • Rusted damper
  • Musty odors emerging from the fireplace 
  • Water in the firebox
  • White staining occurring on the exterior masonry
  • Dampness on the ceiling or walls that are adjacent to the chimney  

How to Repair Chimney Brick Spalling?

If you’re in a situation where you haven’t been able to prevent brick spalling, you need to take the right steps to repair the issue so that it doesn’t progress into something far worse. 

The first thing to do in case of chimney brick spalling is to get the opinion of an expert who can suggest the right steps to take to treat the issue on the basis of the inspection. 

The type of treatment required will depend on the extent of damage that has taken place.

In the early stages, using a waterproofing sealant for the bricks and repairing the crown can tackle the problem of brick spalling. 

You can also install a new chimney cap or repair/replace an old one. Installing a cricket can help to direct water away from the chimney in case of exposure to excess water flow.    

Late-stage treatment of brick spalling will require the repair and replacement of brickwork based on how much damage has occurred. 

Some situations may require just a few bricks and mortar seams to be replaced, while other situations may necessitate the rebuilding of the chimney to avoid a collapse. 

The removal and replacement of damaged mortar to add fresh mortar are done through a process called “tuckpointing.” 

This helps to restore the stability and appearance of the chimney. On completion of the masonry work, a waterproofing sealant must be added, and a new chimney cap must be installed.        

If there are very few spalled bricks, you can even replace them yourself. Here’s what you’ll need: 

  • A drill and cold chisel
  • Mortar and water
  • Club hammer
  • 6-8 mm masonry bit
  • Replacement bricks
  • Sharp trowel

Here’s what you should do:

  • Assess the chimney to identify root causes, fix leaks, and get an idea of how many bricks need to be replaced.
  • Use replacement bricks that match the ones being removed. Stick with the same pointing style of fixing mortar joins between bricks.   
  • Using a cold chisel, club type hammer, or a masonry bit to drill holes into the brick, make it crumble so that it’s easier to take out. 
  • Properly apply new mortar using mortar that’s porter-cement-based or even a mix of lime and sand.    
  • Dampen the region being repaired and apply the mortar to the base and sides using a sharp trowel. Make the layer 10mm thick.    
  • Place the brick in line with its surrounding area and work on it with the trowel handle to give it a uniform look. 

If this seems complicated, just call in a professional to help you.

Tips for Hiring a Professional Chimney Company

I know, it’s a lot to consider. 

But that doesn’t mean that it has to be a stressful task. You can easily reach out to your local chimney company and have a done-for-you solution in no time!

But navigating through all of the chimney companies in your city can be a chore all on its own. And it makes sense, too. 

Hiring anyone to come into your home to fix something like your chimney shouldn’t be a task you take lightly. So I created a list that you can use to make sure you make the right decision when you need someone to help you in your home. 

Questions to Ask

When you’re hiring a chimney company, you should always ask the following questions before allowing them to come into your home:

  1. Can the company provide references? 
  2. Does the company carry a valid business liability insurance policy? 
  3. Does the company ensure that a certified chimney technician will be on the job? 

If they guarantee all three of those, then you are in a good spot. The technicians don’t necessarily need to be certified by the CSIA, but I do recommend putting in a bit more due diligence before accepting a certification that’s not by the CSIA. 

This is because certifications are a tricky thing, especially in an unlicensed industry like ours. Any company can craft a list of job-related questions and sell them as an exam and certify those who pass. 


I recommend you take a few extra minutes in your research before making your hiring decision to learn more about the certification the company has. Here are a few tips to make sure the certification is reputable: 

  • Is the word “certified” just part of the business name or is it an earned designation? 
  • Is the certifying body a for-profit business or non-profit? 
  • Does the certification need to be maintained and renewed through continuing education as the industry evolves, or is it well enough to be certified through a one-time exam? 
  • Is the certifying body well-established or are they relatively new to the scene? New doesn’t mean “bad” but you should make sure the requirements for certification are more or at least equally stringent as those of more established certifications
  • Is the mission statement of the certifying body focused on educating and protecting homeowners or is it more focused on making it easier to earn a certification? 
  • Does holding the certification require following a code of ethics? 

If you can answer all of these questions, then I think it will be safe to allow the company in your home to work on your chimney.

Schedule an Inspection

The good news with this list is that most of them can be avoided. 

All you need to do is make sure you are giving your chimney and fireplace the love and attention that they desire. That means scheduling an inspection with a certified chimney expert. 

We’ll be able to look at your chimney, inside and out, and determine if it is in safe and efficient working order. 

An annual inspection (and maybe a cleaning) is all you need to keep your peace of mind with your chimney.

Patriot Chimney has a few CSIA Certified Chimney Sweeps that you can trust with your home and family. During your service, you can expect your technician to inspect your chimney with a video camera so we can give a full top-to-bottom, inside out inspection. 

We’re licensed, insured, certified, and guarantee you’ll be happy with your service.


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