Although most people would list chimney fire as the biggest threat to their chimneys, the Chimney Institute of America (CSIA) says otherwise. According to CSIA, nothing poses a bigger threat to the chimney than water exposure.
Whether in liquid or vapor form, water poses a massive threat to the chimney’s structural integrity. The worst part is that chimneys are exposed at the top of the roof, completely exposed to rain and snow. It makes shielding the chimney from water damage an incredibly challenging task.
If used alongside other approaches, chimney water repellent can help minimize the water that gets into the chimney.
Shortly, we’ll discuss, in detail, how chimney water repellents work and how to choose the right one for your application. First, though, a review of some of the best chimney repellents;
Chimney Water Repellent Buying Guide
The masonry materials used to build chimneys are porous. From bricks to stone and mortar, they all absorb moisture with ease. When exposed to rain, these materials will soak up and can retain water for a long period.
The water alone is enough to weaken masonry materials. However, there’s something even worse when water is trapped inside bricks, stone, and mortar – condensation.
During the cold weather, water freezes, turning into solid. Frozen water occupies a bigger volume. This increase in volume can cause significant stress inside the mortar and other masonry materials. At the very least, it causes the material to expand slightly.
Studies show that if the mortar contains more than 6% water, the expansion due to freezing is great enough to crack the mortar. Remember that water condensation on masonry units’ surface can also prevent a good bond between the mortar and other masonry units.
Other Ways Water Can Damage the Chimney
It’s not just cracking you should be worrying about, though. Water from rain or snow can also damage the chimney in the following ways;
Nearly all masonry chimney materials, including blocks, mortar, and stone, easily absorb moisture. As we’ve established, during the cold weather, the water inside the masonry freezes, effectively increasing in volume. This can cause what’s known as spalling.
Spalling, sometimes incorrectly called “spalding” or “Spaulding,” forces the surface of blocks and general masonry work to peel, pop out, and flake off. Some people also call it flaking. It happens when moisture (and salt) inside the material pushes outward. Spalling can eventually cause crumbling and structural disintegration.
The easiest way to spot spalling is to watch for exterior damage to your chimney. If you see bits of bricks around the chimney base, it could be a sign of spalling.
Rusting and Liner Deterioration
Water seeping into the chimney can also cause or speed-up rusting of metal components therein. If you notice that your firebox is rusting, for instance, the most likely cause is water leakage via the chimney. The damper is another component that easily rusts when exposed to water or moisture.
In addition to rusting, water can also impact the flue liner. The liner is the smooth material covering the surface of the flue. Most masonry chimneys have either metal (stainless steel or aluminum) liners or clay tile linings. Water leakage can cause metallic liners to rust and clay tile liners to corrode and crack.
Here, all you need to verify the presence of water damage is the rust itself. Remember that rust may also be hidden. So, a thorough inspection may be needed.
Finally, damage to the chimney occasioned by exposure to water can also cause chimney leaks. First off, bricks and water both pass water. Moreover, we’ve seen that water damage can cause bricks to crack and mortar to spall. The resulting large gaps within the masonry may allow water from outside to find a way inside your home.
Secondly, leaks can originate from the chimney crown. The crown is the cement part of the top of the chimney. Cement passes water too. Like in brick and mortar, exposure to water can cause cracks within the cement, allowing even more water into the chimney.
If you can see pooling water on the floor right below the chimney, it may be water leaks. Another sign of water leaks is the rusting of the stove and the damper inside.
What is a Chimney Water Repellent?
Chimney water repellents are treatments, usually in liquid or powder form, that penetrate masonry, often up to ¼ inch or more depending on the material’s surface porosity and moisture content at the time of repellent application.
These solutions work by reacting with the minerals in masonry to form strong permanent bonds beneath the masonry material’s surface that prevents water from penetrating the material while allowing moisture to escape via the same chimney walls.
Though the majority are spray-on, chimney water repellents come in different types. Some are solvent-based, while others are water-based. Your chimney technician will help you determine the right type for your application.
Most experts recommend water-based repellents. Water-based chimney water repellents are typically vapor-permeable, i.e., release water vapors that would otherwise pass to the bricks when the chimney is in use. They effectively block 99.9% of water penetration.
Benefits of Chimney Water Repellent
The benefits of waterproofing your chimney via water repellent solutions are endless. The following are just a few reasons to strongly consider this option;
- Save on future repairs: Left unchecked, chimney water damage can rage your chimney, necessitating expensive repairs down the line. Waterproofing with chimney water repellent prevents such damage.
- Increase chimney efficiency: A leaky chimney is an inefficient chimney. The water dropping from above greatly compromises the combustion process down in the stove, resulting in poor flames. Waterproofing helps eliminate this problem.
- Slow down chimney damage: It’s impossible to prevent the chimney’s natural wear and tear. However, by preventing spalling and cracking, you significantly slow down the deterioration process.
- Prevent staining and fungi: A leaky chimney quickly undergoes efflorescence (water staining). The seeping water may also compromise the chimney’s natural appearance and potentially cause the growth of mildew. Applying water repellent helps address these issues.
Things to Consider When Choosing the Best Chimney Water Repellent
There are a couple of things to keep in mind when shopping for chimney water repellent. First off, there are two main types of water repellents – solvent-based and water-based. Most people prefer water-based repellents as they are more breathable.
The other consideration is the size of the chimney. The amount of repellent needed to complete the project will depend on the surface area of the chimney. Calculate the area of each surface and add them up to determine the total area.
Finally, it’s also worth considering the warranty of the product. Long warranties back the best chimney water repellants, typically ten years or longer.
Chimney Water Repellent FAQs
Why Does the Chimney Leak when it Rains?
There can be many reasons. Perhaps the chimney cap is missing, or the chimney flashing is leaky. It could also be the result is a leaky top pan on the chimney chase. However, often, it’s a sign of deteriorated mortar, chapped chimney crown, and, in general, leaky masonry.
Why Should You Waterproof a Chimney?
The main reason you should waterproof your chimney is that chimneys are naturally exposed to rainwater and snow. Rainwater and snow can cause massive damage to the chimney, from rusting of the stove down below to flue staining and spalling. Over an extended period, these damages can necessitate costly repairs.
How Much Does it Cost to Get Your Chimney Waterproofed?
The average cost of a chimney waterproofing job is $250. However, the actual price may vary depending on the exact tasks of the waterproofing project.
Leak repairs, for instance, cost $150 to $350, sealing costs $180 to $350, and flashing costs $200 to $350. Water repellent application (including labor) costs around $50-$100.
Best Chimney Water Repellent
1. Chimney-RX Brushable Chimney Crown Repair
- Fast-setting, Flexible Coating that Seals and Protects Chimney Crown Tops - Repairs Cracked Chimney Crowns and Prevents Chimney Leaks
- Stops Chimney Water Leaks & Repairs Chimney Crown Cracks
- Specifically Formulated to Repair and Protect Fireplace & Chimney Crowns from Water Intrusion
- Covers Approximately 40 Square Feet per Gallon
- Easy to Apply With a 3 Inch or 4 Inch Paint Brush, & Cures in 2-4 Hours
Chimney-RX Brushable Crown Repair is a fast setting elastomeric coating that forms a flexible waterproof membrane. It’s specifically created for use in repairing and protecting the chimney crown from water intrusion.
The sealant is easy to apply. All you need is a 3-4-inch paintbrush. The formulation is already in good order – no further mixing is needed. You also don’t need any special bonding agents.
Above all, the component compounds are solvent-free, thus don’t harm the environment. The sealant cures within as little as four hours, though you may need to wait for up to four hours for some chimney types. Weather conditions, especially humidity and temperatures, are other factors that affect drying times.
Consider this crown repair sealant whenever you need a long-lasting exterior waterproofing membrane, such as when repairing chimney crowns, chimney corbels, and tops of chimney masonry. One gallon serves approximately 40 square feet.
- Fast setting, flexible coating
- Cures in 2-4 hours
- Clear in color
- One gallon = 40 square feet
- You need to work fast (as it dries quickly)
- No warranty
2. Chimney Brick Sealer, Clear Water-Based Siloxane Sealer
- CLEAR PROTECTION – Provides a long-lasting, non-glossy invisible coat to masonry surfaces. Will never leave any residue or alter the color or appearance of your brick chimney, stone chimney, or other type of masonry chimney. Masonry waterproofer that will last for up to 5 years
- WATER REPELLENT – Water-based, siloxane penetrating brick sealer that bonds with the minerals in masonry to provide with you long-lasting water protection. The breathable sealer causes the water to bead instead of seeping into the brick pores, causing chimney leaks
- POWERFUL CHIMNEY SEALER – Keep your chimney leak free and protect it or other masonry surfaces from spalling, flaking, or cracking. Best suited to protect against freeze thaw damage, and white efflorescence.
- EASY TO APPLY – First step is to ensure your chimney or masonry surface is fully cleaned and clear of dirt, dust, grease, oil, efflorescence, etc. Use a low-pressure pump-up garden sprayer to evenly coat your chimney. 1 gallon will give 90-150 sq.ft. of coverage
- 5 YEAR WARRANTY – MasonryDefender offers a 5 Year Limited Warranty on Vertical Masonry Surfaces
The Clear-Protection Masonry Defender chimney brick sealer is another water-repellent solution that provides a long-lasting, non-glossy invisible coat to protect your masonry from water penetration.
It doesn’t leave any residue or alter your brick chimney’s color/appearance or stone chimney and can last up to five years before reapplication.
The repellent is water-based, thus eco-friendly, but penetrates brick exceptionally well and bonds with the masonry minerals to provide long-lasting protection. The breathable sealer causes water to bread rather than seep into your chimney masonry. This effectively prevents chimney leaks.
It’s an easy-to-apply sealant. Just make sure your chimney masonry is cleaned up and clear of dirt, grease, oil, efflorescence, etc. then, use a low-pressure pump sprayer to coat your chimney evenly. One gallon can serve 90-150 square feet.
- Provides long-lasting repellency
- Non-film forming
- One gallon serves up to 150 square feet
- 5-year limited warranty
- Warranty only applies to vertical chimneys
- Slight darkening may occur on dense surfaces
3.Rainguard Blok-Lok 1-Gallon Professional Grade Water Repellent Sealer
- 100 percent breathable water repellent for vertical concrete, brick and masonry surfaces
- Dries with a natural finish that will not yellow
- Protects against water intrusion, efflorescence, lime, spalling, freeze/thaw damage, stains, mold, mildew, and uv damage
- , water-based, & made in usa
- Backed by FIVE year material
The Rainguard Blok-Lok Silane water repellent is another value-for-money choice when shopping for a sealant to protect your chimney from rainwater and snow penetration.
It is a ready-to-use, 100% active, water-based sealant with low volatile organic compounds (VOC) content. It also very clear, thus doesn’t change the appearance of masonry chimneys.
The formulation comprises a unique blend of silane/siloxanes and exclusive Micro-Lok elements, forming a long-chain water-repellent barrier that repels water and salts while remaining highly vapor-permeable.
You don’t need to mix it with any compounds or solvents – use it right out of the container. Every purchase earns you a 5-year labor and material warranty (you need to fill a warranty form).
This sealant is best for vertical concrete, block, brick, and other porous surfaces and forms a long-chain water repellent barrier. Each gallon can serve up to 100 square feet.
- 100% moisture-permeable
- 93% chloride ion intrusion reduction
- 1 gallon covers up to 150square feet
- 5-year warranty
- May contain carcinogens
4. Rubberseal Liquid Rubber Waterproofing and Protective Coating
- Liquid Rubber Waterproofing and Protective Coatings Product
- Insulating, Ceramic Properties Great for Roofs and RV Roofs
- Resistant to Aging and UV Exposure
- Low VOC, Excellent Elongation
- Spread Rate: 60 sq ft/gal at 20 imperial mils
Rubberseal Roll-On liquid rubber is a water-based, low VOC, UV resistant, EPA star rated rubber membrane designed to protect and waterproof various household and industrial items.
It offers superior flexibility and extra durability for applications requiring waterproofing. That’s because it’s a high-end emulsion that exhibits tremendous bond strength and offers exceptional chemical resistance.
It is also puncture resistant and offers excellent elongation. The best part is that it installs easily, cures quickly, and develops unmatched film strength.
The sealant is ideal for waterproofing in the most demanding applications. Aside from sealing chimneys to keep water out, you can use the remaining solution in fountains, drainage systems, ponds, RVs, and even gutters.
- Covers 60 square foot per gallon
- EPA Energy Star Rated
- Resistant to aging and UV exposure
- Self-healing and excellent elongation
- Has a dark grey color
5. Dry-Treat Stain-Proof Premium Impregnating Sealer
- DEEP CLEANING: Our powerful sealer includes a super penetrator to access dense granite and marble.
- REINFORCED PROTECTION: Our sealer protects against stains and damage from water, salt, and oil.
- BREATHABLE: This formula allows water vapors to escape freely, preventing harmful moisture buildup.
- MAXIMUM STAIN REPELLENCE: This sealer has 3 custom sealing molecules for 3 levels of penetration.
- VERSATILE: Our sealer works on many countertops, like basalt, bluestone, concrete, and quartzite.
Dry Treat’s Stain-Proof Premium Impregnating Sealer is an invisible and breathable sealant that provides premium long-lasting protection.
Aside from water, it helps protect against oil-based stains, efflorescence, picture framing, and freeze-thaw damage. Another thing that sets it apart is that the treated surfaces are easier to clean and retain breathing ability.
The sealant works excellently in nearly all masonry chimney types, from tile to concrete and brick. It can also be used on countertops, building facades, floors, walls, showers, and swimming pools. You’ll also appreciate that it stands up to alkaline cleaners and pressure washing. It’s also resistant to dissolved salts, often found in rainwater.
Stain-Proof impregnating sealers are a little different from typical ware repellents. The molecules penetrate deeper into porous material and bond permanently inside the pores without blocking them. This ensures a long life of weather resistance.
- Forms permanent bonds in porous materials
- Creates a permanent oil and water-repelling barrier
- Useful in many application, domestic and industrial
- Retains natural surface and color
- No mention of warranty
6. Liquid Rubber Waterproof Sealant
- PROTECTIVE FINISH FOR - Flat roofs, metal roofs, sloped roofs, planter boxes, foundations, sheds, basements, metal, wood, concrete and more
- HIGHLY FLEXIBLE & DURABLE - Final membrane has over 1000% elongation preventing adhesion failure, and is UV Stable stopping the sun from degrading the product
- COVERAGE - Vertical Surfaces - 1 gallon/30 sq ft (2.8 sq m). 3-4 heavy coats to achieve a 30 mil (0.76 mm) membrane. Flat/Ponding Surfaces - 1 gallon/15 sq ft (1.4 sq m). 4-5 heavy coats to achieve a 60-80 mil (1.5-2 mm) membrane
- ENVIRONMENTALLY FRIENDLY - Liquid Rubber Waterproof Sealant/Coating is water based, containing no solvents, VOC's or harmful odors. Safe for humans and pets alike, can be used indoors and outdoors with no special breathing apparatus
- FOR A BULLETPROOF SYSTEM - Bridge joints, seams, vents, gaps, protrusions…. With Liquid Rubber Seam Tape or Liquid Rubber Geo-Textile where possible movement may occur
Another protective finish ideal for many different applications, the liquid rubber waterproofing sealant from LR is a highly durable and flexible membrane with a 1000% elongation.
This makes it an excellent choice for roofs, foundations, basements, and concrete surfaces, among others. It is UV-stable and highly adhesive.
The liquid rubber sealer is water-based, thus environmentally friendly. It contains no solvents, VOCs, or harmful odors. A gallon of the sealant can cover 30 square feet when used in vertical applications and about 15 square feet for horizontal applications. Remember that you need multiple coats (ideally 3 or 4) to achieve the best sealing membrane.
The sealant is easy to apply. Also, you don’t need to mix it with any other solutions. Just open the container and start applying it. Use a brush or roller for application.
- Exceptionally flexible
- Easy to apply
- Endless applications
- No solvents or VOCs
- No warranty
- It can harden if left for too long
7.Eco Advance EACON16CON Waterproof 16oz Concrete/Masonry Water Proofer
- Liquid concentrate formula makes 1 gallon of commercial grade water proofer
- Ideal for use on concrete, brick, stucco, stone (natural and synthetic), EIFS, pavers and more
- Protects against water damage, oil, stains, mold, mildew, de-icing salts, and pool/spa chemicals
- Water-based, non-toxic, non-flammable formula does not harm landscape plantings
- Vapor permeable (breathable) water proofer can be used on new concrete and masonry
Finally, the spray-on Eco Advance formula is another low-cost solution when shopping for a chimney sealant. It is a commercial-grade water-based repellent with excellent breathing qualities, allowing for long-term product and substrate performance.
It also has a way of preventing moisture from being trapped in the masonry. Trapped moisture can lead to rapid degradation of the substrate.
The repellant can be used on new or existing concrete and masonry chimneys and provides invaluable protection from harmful UV rays. It dries without changing the chimney’s surface appearance and protects from water damage, mildew, de-icing salts, and most chemicals.
The 16oz container is enough to seal a 240 square-foot area. Therefore, you can use the sealant for several rounds of application. Alternatively, you can use it for pavers, stucco, split-face blocks, and exterior insulation and finish systems.
- Cures in less than two hours
- Eco-friendly and low VOC content
- Low odor formula
- Vapor permeable
- No mention of warranty
- Application device not included
Water is arguably the chimney’s biggest enemy. Extended exposure to water sources, including moisture, rainwater, and snow, can cause the chimney masonry to crack, spall, and chip away.
It can also cause staining and chimney leaks. If you haven’t done so yet, consider waterproofing your chimney with a chimney water repellent to prevent costly repairs.