Best Chimney Waterproofing Products: Stop Leaks & Protect Your Masonry (Review)
Water is the silent destroyer of masonry. Unlike the catastrophic damage of a chimney fire, water damage is insidious. It seeps into the microscopic pores of your bricks, freezes, expands, and slowly crumbles your chimney from the inside out. By the time you see the moss growing or the spalling bricks on your lawn, the structural damage is already done.
If you have noticed a leaky chimney or simply want to extend the lifespan of your masonry, applying a high-quality water repellent is one of the highest ROI maintenance tasks a homeowner can perform. But not all sealers are created equal. In fact, choosing the wrong “sealer” (like a film-forming paint) can actually accelerate damage by trapping moisture inside.
In this comprehensive guide, we test and review the best chimney waterproofing products on the market. We analyze their chemical composition (Silane vs. Siloxane), breathability rating, warranty, and ease of application to help you shield your home against the elements.
Quick Comparison: Top Waterproofing Picks
| Product | Best For | Base Type | Warranty |
|---|---|---|---|
| ChimneySaver Water Repellent | Overall Best (Pro Choice) | Siloxane | 10 Years |
| SaverSystems Chimney Rx | DIY Friendly | Silane/Siloxane | 10 Years |
| Ghostshield Siloxa-Tek 8500 | Heavy Duty Industrial | Silane/Siloxane | 100 Years (Structural) |
| Rain Guard Water Sealers | Eco-Friendly | Micro-Lok Acrylic | 5 Years |
Why “Sealing” Your Chimney is a Mistake (Read This First)
Before we dive into the product reviews, we must clarify a massive misconception in the industry: the difference between sealers and water repellents.
The Breathability Factor
Bricks are like sponges—they are naturally porous. They absorb water during rain and release it through evaporation when the sun comes out. If you use a film-forming sealer (like a clear coat paint or a generic concrete sealer found at big-box stores), you create a plastic-like barrier over the brick.
While this stops rain from getting in, it also traps internal moisture (from your home’s humidity or flue condensation) inside the brick. When that trapped moisture freezes in winter, it expands, popping the face of the brick off—a process known as spalling. This is why you should check out our guide on best paint for chimney brick to understand which coatings are breathable.
The Solution: Penetrating Water Repellents. The products listed below are 100% vapor permeable. They dive deep into the pores to create a hydrophobic zone that blocks liquid water but allows water vapor to escape. This is the only safe way to waterproof a chimney.
Deep Dive: The Best Chimney Waterproofing Products
1. ChimneySaver Water Repellent Top Choice
The Industry Standard used by Chimney Sweeps across North America.
If you hire a professional chimney sweep to waterproof your stack, there is a 90% chance they are using ChimneySaver. This is a commercial-grade, siloxane-based water repellent specifically engineered for vertical masonry surfaces.
Unlike hardware store sealers that degrade under UV light within 12-24 months, ChimneySaver forms a chemical bond with the silica in the brick. It creates a hydrophobic barrier that is practically invisible, maintaining the natural look of your brick without a glossy sheen.
Pros
- 100% Vapor Permeable (allows bricks to breathe)
- Non-glossy finish (invisible protection)
- Resistant to mildew and fungus
- 10-Year Warranty available
- Prevents efflorescence (white salt stains)
Cons
- More expensive than hardware store brands
- Requires proper overspray protection for windows
- Requires dry weather for application (6-hour cure time)
Verdict: If you want to do the job once and not worry about it for a decade, this is the product to buy. It is the best defense against freeze-thaw damage.
2. SaverSystems Chimney Rx Masonry Chimney Water Repellent
Best DIY-Friendly Option for Older Bricks.
From the same parent company as ChimneySaver, the Chimney Rx line is formulated specifically for the consumer/DIY market. While sharing much of the same DNA as the pro version, Chimney Rx is slightly more forgiving during application.
It utilizes a silane/siloxane blend. The silane molecules are smaller, penetrating deep into the substrate for structural protection, while the larger siloxane molecules stay near the surface to bead water. This “one-two punch” makes it excellent for older, slightly more porous chimneys that haven’t been maintained in years. It pairs excellently if you have recently repaired joints using the best mortar for chimney repair.
Pros
- Deep penetration (up to 1/4 inch)
- Excellent water beading effect
- Water-based (lower VOCs than solvent-based)
- Easy cleanup with soap and water
Cons
- Can darken some very light sandstones slightly
- Not intended for horizontal surfaces (like the crown)
3. Ghostshield Siloxa-Tek 8500
The High-Tech Heavyweight for Extreme Climates.
Ghostshield creates industrial concrete sealers, and the Siloxa-Tek 8500 is a marvel of nanotechnology. If you live in an area with harsh winters (heavy snow, ice, and rapid temperature fluctuations), this is your armor.
It is a highly concentrated silane/siloxane sealer that you often buy in a concentrate and mix with water. Its defining feature is its resistance to de-icing salts. While you likely aren’t salting your chimney, coastal homes exposed to sea spray will benefit immensely from this salt-resistant formula. It helps prevent spalling and cracking better than almost any other consumer product.
Pros
- Industrial strength nanotechnology
- Resistant to salt degradation (great for coastal homes)
- Very high coverage rate
- Does not alter surface appearance
Cons
- Often sold as concentrate (requires mixing)
- Higher price point per gallon
- Overkill for mild climates
4. Rain Guard Water Sealers (Brick Sealer)
The Eco-Friendly, Budget-Conscious Choice.
Rain Guard offers a distinct technology called Micro-Lok. Instead of relying solely on silanes, it uses a proprietary blend that creates a mechanical bond. It is incredibly popular due to its eco-friendliness—it has low VOCs and is safe to use around plants and pets, which is a concern for many homeowners spraying chemicals from a roof.
While it may not have the 10-year longevity of ChimneySaver, it is significantly more affordable and easier to find. For a quick weekend project to seal a chimney before the rainy season, Rain Guard is a solid contender.
Pros
- Very affordable
- Eco-friendly and safe for plants
- Ready to use (no mixing)
- Fast drying time (1-2 hours)
Cons
- Shorter lifespan (needs re-application sooner)
- Less penetration depth than silanes
Buying Guide: How to Choose the Right Product
Before you click “buy,” consider these factors to ensure compatibility with your specific chimney setup.
1. Water Base vs. Solvent Base
Water-based repellents (like ChimneySaver water-base) are easier to clean up, have less odor, and are compliant with strict VOC laws in states like California. Solvent-based repellents cure faster and can sometimes be applied in colder temperatures, but they are messier and smell stronger.
2. The “Crown” Exception
Remember, the products listed above are for the vertical brick walls of the chimney. They are NOT for the chimney crown (the concrete slab on top). The crown requires an elastomeric coating because it faces direct vertical rain impact and snow accumulation.
If your crown is cracked, you need a different product entirely. Check out our guide on best chimney caps for rain and crown repair solutions.
3. Climate Considerations
If you live in the Northeast or Midwest, where freeze-thaw cycles are brutal, invest in the Siloxane based products (ChimneySaver or Ghostshield). If you are in a milder, rainy climate like the Pacific Northwest, a standard silane/siloxane blend works perfectly.
Step-by-Step: How to Waterproof Your Chimney
Buying the product is only half the battle. Application technique determines success. For a full detailed walkthrough, read our master guide: How to Waterproof a Chimney. Here is the condensed version for this product review:
Step 1: Inspect and Repair First
Do not waterproof a dirty or broken chimney. If you have missing mortar, the water repellent won’t bridge the gap.
- Fix cracks with chimney flashing sealant or new mortar.
- Remove moss and mold using a pressure washer (low pressure) or a stiff brush.
- Remove efflorescence (white stains) with a specialized cleaner.
Step 2: Calculate Coverage
Most gallons cover 100–150 square feet. A typical single-story chimney might need 1 gallon, while a large two-story stack might need 2–3 gallons. Always buy a little extra.
Step 3: Application
Use a garden pump sprayer for the best results. Start from the bottom and work your way up. This prevents “rundown” streaks that can stain the brick below. Apply a “flood coat”—meaning you spray enough that the liquid runs down the face of the brick about 6 inches. This ensures deep saturation.
Beyond Waterproofing: Total Chimney Health
Waterproofing protects the bricks, but water can enter through other vulnerabilities. To fully seal your system, consider:
- The Flashing: The metal seal between the chimney and roof is a common leak point. Learn more in our guide to best chimney flashing sealant.
- The Cap: An open flue is a bucket waiting to catch rain. Ensure you have a quality cap installed (read our review here).
- The Crown: As mentioned, use a brushable crown sealer for the top slab.
If the damage is already severe (loose bricks, leaning stack), waterproofing is a band-aid. You may need professional masonry work. Check our guide on best chimney services to find a pro.
Frequently Asked Questions
Can I use Thompson’s Water Seal on my chimney?
While Thompson’s is a popular brand, many professionals advise against using standard deck sealers on masonry. Some formulations are film-forming and can trap moisture, leading to spalling. Always check the label to ensure the product is 100% vapor permeable and approved for vertical masonry.
How often should I waterproof my chimney?
If you use a high-quality professional siloxane product like ChimneySaver, it can last 10 years or more. Cheaper hardware store brands typically need re-application every 2 to 3 years. Visual inspection is key: spray water on the bricks; if it darkens the brick instead of beading up, it’s time to re-apply.
Will waterproofing change the look of my bricks?
Most silane/siloxane water repellents dry clear and matte, leaving the brick looking natural. However, some can slightly darken the substrate or leave a slight sheen if over-applied. Always test a small, inconspicuous area first.
Can I apply water repellent over painted brick?
No. Penetrating water repellents need to soak into the pores of the masonry. If the brick is painted, the pores are blocked. You would need to strip the paint first or simply maintain the paint layer. For painting tips, see our guide on chimney paint.
Final Verdict: Which Product Should You Buy?
Your chimney is highly exposed to the elements. Protecting it now saves thousands of dollars in tuckpointing and rebuilding costs later.
- For the best long-term protection: Go with ChimneySaver Water Repellent. It is the gold standard for a reason and offers the best breathability profile.
- For harsh, freezing winters: Choose Ghostshield Siloxa-Tek 8500 for its industrial durability against salt and ice.
- For a budget-friendly DIY fix: Rain Guard is a safe, easy entry point.
Don’t wait for the first freeze of the year. Apply your waterproofing while the weather is mild and dry. If you are unsure about the condition of your chimney structure, always consult a certified sweep. For more maintenance tips, check our article on how often should you clean a chimney.