Chimney Waterproofing: A Step-By-Step Guide for DIYers

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Your chimney is one of the essential parts of your home, and it’s important to keep it in good condition. Chimney waterproofing is one way to help protect it from the elements and extend its life.

There are a few different ways to waterproof your chimney, and the best method for you will depend on the materials your chimney is made of and the type of climate you live in. Either way, waterproofing a chimney is a relatively easy DIY project you can do in a day or two.

But how do you know if your chimney needs to be waterproofed? And what should you use to waterproof it? Here’s everything you need to know about chimney waterproofing, including a step-by-step guide.

What is Chimney Waterproofing?

Chimney waterproofing is the process of adding a waterproof barrier to your chimney to prevent leak repair issues. Water can cause many problems for chimneys, including cracking, eroding the mortar between bricks, and rusting metal parts.

Chimney waterproofing can help to prevent these problems and extend the life of your chimney. There are several ways to waterproof a chimney, including using chimney sealants, coatings, or membranes.

No matter which option you choose, chimney waterproofing is an essential step in protecting your chimney from water damage.

Is Chimney Waterproofing Necessary?

There is every reason to waterproof your chimney, whether it is made of brick, stone, or mortar. Waterproofing protects against the damaging effects of water seepage and chimney leaks in heavy rain, which can lead to severe problems such as structural damage, mold and mildew growth, and deterioration of the chimney itself.

Here are the main benefits of chimney waterproofing:

Prevents Water Seepage and Damage

If left unchecked, water seepage can lead to cracks in the chimney structure, which can cause the chimney to collapse due to deterioration.

Waterproofing can also help prevent mold and mildew growth, which can not only cause damage to the chimney but also harm your health.

Improves the Longevity of the Chimney

A well-maintained and waterproofed chimney can last for 50 or more years, while an unprotected chimney is likely to succumb to water damage and other problems much sooner.

Saves Money in the Long Run

Chimney waterproofing is a relatively inexpensive process, especially when compared to the cost of repairing or replacing a damaged chimney. By waterproofing your chimney now, you can save yourself a lot of money down the road.

If you are unsure whether your chimney needs to be waterproofed, it is always best to consult with a professional. They can assess the condition of your chimney and advise you on the best course of action.


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How to Waterproof a Chimney Stack

As mentioned, waterproofing a chimney isn’t a difficult task. However, you’ll need to consider a few factors before getting started, such as the type of chimney you have and the condition of the mortar joints.

If you’re unsure how to waterproof your chimney, we’ve put together a quick guide to help you get started.

DIY Disclaimer

Waterproofing a chimney requires you to have a steady hand and to follow directions carefully. Make sure you’re comfortable with the task before beginning. With that in mind, you’ll need the following materials to get started:

  • Protective gear: Always wear gloves, goggles, and a mask when working with chemicals.
  • Chimney sealant: We recommend using a water-based sealant for easy cleanup.
  • Mortar joint raker or wire brush: You’ll need this to clean the joints between bricks.
  • Roller: Used to apply the chimney sealant.
  • Water hose: Used to wet the chimney before applying the sealant.

Now that you have all the materials let’s get started.

Step 1: Measure Your Chimney’s Surface Area

The first step is to measure the surface area of your chimney, which will help you determine how much sealant you’ll need to purchase. Measure all the sides of the chimney, including the top and bottom.

Once you have all the measurements, add them up to get the total surface area. Knowing the surface area is also essential because some sealants must be applied when the chimney is wet, while others can be used on a dry chimney.

Step 2: Inspect the Chimney’s Mortar Joints

The next step is to inspect the mortar joints between the bricks. These joints allow water to seep into the chimney, so they must be in good condition before applying the sealant.

Use a mortar joint raker or wire brush to clean out any joint debris. If the joints are cracked or damaged, you’ll need to repair them with new mortar before waterproofing the chimney.

Step 3: Clean Your Chimney

Now that the mortar joints are clean, you’ll need to give the rest of the chimney a good cleaning and sweep away any loose debris, such as leaves or bird nests.

If there is any dirt or grime on the bricks, use a stiff brush to scrub them away. You can also use a pressure washer to clean the chimney, but be careful not to damage the bricks.

Step 4: Cover Unwanted Areas

Use a drop cloth or tarp to cover non-target items or areas and protect them from the sealant. Additionally, you can put some plastic sheeting around the base of the chimney to protect against any drips.

Step 5: Do Necessary Repairs

If your chimney has cracks or damage, now is the time to make the repairs. You can use a waterproofing sealant or hydraulic cement to patch any cracks.

For larger areas of damage, you might need to replace some bricks or the entire chimney. Consult with a professional if you’re unsure how to proceed.

Step 6: Settle on a Water Repellent

After you’re through with repairs, it’s time to choose a water repellent. The sealant you use will depend on your chimney’s surface area and the bricks’ condition.

If your chimney is large or the bricks are in poor condition, we recommend using a masonry waterproofing sealer. This type of sealer penetrates deep into the bricks and provides long-lasting protection.

You can use a waterproofing spray for smaller chimneys or those in good condition. This type of sealer will provide adequate protection but won’t last as long as a masonry sealer.

Step 7: Wet the Chimney

Now that you’ve chosen a sealant, it’s time to wet the chimney. This step is only necessary if you’re using a masonry waterproofing sealer.

If you’re using a spray sealer, you can skip this step. Use a water hose to wet the entire chimney, including the top and bottom. Finally, allow the chimney to soak for at least 30 minutes.

Step 8: Apply the Sealant

Once the chimney is wet, it’s time to apply the sealant. You can use a brush, roller, or sprayer for a masonry waterproofing sealer.

If you’re using a spray sealer, we recommend using a pump sprayer for the best results. Apply the sealer evenly over the entire chimney, taking care to get into all the cracks and crevices.

Step 9: Allow the Sealant to Dry

After you’ve applied the sealant, it’s essential to let it dry completely before using the chimney. Depending on the sealant, this can take anywhere from 24 to 48 hours.

If you need to use the chimney before the sealant is completely dry, you can cover the top of the chimney with a tarp or plastic sheeting. Just be sure to remove the cover before using the chimney.

Step 10: Final Touch-ups

Cleaning up any drips or excess sealant is the final step in waterproofing your chimney. Once the sealant is dry, you can remove any plastic sheeting or tarps.

If there are any drips on the bricks, you can use a putty knife or wire brush to scrape them away. For more stubborn drips, you can use a power washer.

And that’s it! By following these ten steps, you can waterproof your chimney and prevent costly repairs in the future. However, it’s important to note that waterproofing is not a substitute for regular chimney maintenance.

Be sure to have your chimney inspected and cleaned by a professional yearly to prevent any future problems.


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How Long Does Chimney Waterproofing Last?

Chimney waterproofing can last anywhere from 15 to 20 years. However, it is crucial to keep an eye on the condition of your chimney and have it inspected regularly. If you notice any cracks or leaks, it is essential to have them repaired as soon as possible to avoid further damage.

There are a few things you can do to extend the life of your chimney waterproofing:

  • Have your chimney inspected and cleaned regularly.
  • Make sure there are no cracks or leaks in your chimney.
  • Apply a fresh coat of waterproofing sealant every few years.

If you follow these tips, you should protect your chimney from water damage for many years to come.

Does Chimney Waterproofing Require a Permit?

Chimney waterproofing does not require a permit in most cases. But if you are planning to do any significant repairs or renovations to your chimney, you may need to obtain a permit from your local building department.

If you are unsure whether your chimney needs waterproofing, you can contact a professional chimney sweeper for an inspection. They will be able to determine if your chimney needs repairs or waterproofing.

Chimney Waterproofing Cost

The average cost to waterproof a chimney is between $150 and $250. However, the price will vary depending on the size and condition of your chimney and the type of waterproofing material you choose.

The cost will be higher if you need to hire a professional chimney sweeper. Professional chimney sweeps typically charge between $75 and $200 per hour, depending on the job’s complexity.

Waterproofing your chimney is a relatively simple and inexpensive way to prevent water damage and extend the life of your chimney. By taking these steps, you can protect your home from expensive repairs in the future.


Chimney waterproofing is essential to the longevity and safety of your chimney. There are many ways to waterproof your chimney, but the most important thing is to use a quality sealant.

Applying a waterproofing sealant is easy, and any homeowner can do it with little experience. However, if you are unsure about waterproofing a chimney, it is always best to hire a professional.

Hiring a professional might cost more upfront, but it will save you money in the long run by prolonging the life of your chimney.

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Thomas Green

Thomas has worked in the Chimney & Fireplace field for over 12 years. He is an expert in his trade and loves to help People with their needs. Thomas Write helpful articles so that homeowners can make the most informed decisions about their fireplace and chimney.