Waterproofing Chimney Masonry in Orland Hills: When It Helps and When It Does Not
By Dan Joel, Elite Sweepers Inc.
Water is the main thing destroying chimneys in this climate, so anything described as waterproofing sounds like an obvious purchase. It can be a good one. It can also be money spent sealing in a problem rather than solving it, and the difference comes down to what condition the masonry is in when it is applied.
What masonry water repellent actually does
The short answer: it reduces how much water the brick absorbs, while still letting moisture already inside escape as vapor.
Brick and mortar are porous by design. They take on water, and in a climate that crosses the freezing point repeatedly, absorbed water is what drives freeze-thaw damage. A breathable water repellent penetrates the surface and makes it far less absorbent, so rain runs off rather than soaking in. Crucially, it remains vapor-permeable, meaning moisture inside the masonry can still dry outward.
Why breathability is the whole point
The short answer: a sealer that traps moisture inside does more damage than no treatment at all.
This is the single most important thing to get right. Products that form a film on the surface, including many general-purpose sealers and paint, stop water going in and also stop it coming out. Masonry always has some moisture in it, and a chimney has moisture arriving from the flue side as well as the weather side. Seal that in and it has nowhere to go but into freeze-thaw cycling behind an impermeable skin, which spalls the brick faces off. A product intended for chimney masonry is formulated specifically to avoid this, and it is not interchangeable with a generic waterproofer.
When it genuinely helps
The short answer: on sound masonry, after any needed repairs, as preventive protection.
- The joints are intact and the brick faces are in good condition.
- Any repointing, crown repair or cap work has already been completed.
- The chimney is fully exposed, which every chimney is, and takes weather on all sides.
- You want to slow the deterioration process on a chimney that is currently fine.
Used that way it is a sensible, relatively inexpensive measure that extends the life of good masonry.
When it does not help
The short answer: when water is entering somewhere other than through the brick face.
Repellent does nothing for a cracked crown, because water there goes down an opening rather than soaking through a surface. It does nothing for failed flashing at the roofline, which is a metalwork problem. It does nothing for an uncapped flue taking rain straight down. And applied over joints that have already receded, it seals the surface of a problem that is now progressing underneath it. In every one of those cases the repair comes first, and the treatment goes on afterward as protection for the finished work.
Our chimney repair page covers repointing and crown work, and our chimney caps and crowns page covers the top of the system, which is where most water actually gets in.
Establishing what you need first
The short answer: an inspection, so the money goes to the right thing in the right order.
We would rather tell you your chimney needs its crown sealed than sell you a treatment that will not address the leak you are worried about. A chimney inspection establishes where water is actually entering, and the sequence follows from there. For local scheduling, see our chimney service in Orland Hills, with costs on our pricing page.
Elite Sweepers Inc is insured and bonded, works seven days a week from 7 AM to 7 PM, and gives you the price before any work begins. Call (708) 432-3977.
Chimney Waterproofing Questions
Should I waterproof my chimney?
On sound masonry, after any needed repairs are done, a breathable water repellent is a reasonable preventive measure in a freeze-thaw climate. On masonry that already has open joints or an unaddressed leak, the repair needs to come first.
Can I use regular sealer on chimney brick?
No. Film-forming sealers and paint trap moisture inside the masonry, which accelerates freeze-thaw damage and spalls the brick faces. Chimney masonry needs a vapor-permeable product formulated for the purpose.
How long does chimney waterproofing last?
It varies by product and by how exposed the chimney is. It is a treatment that needs periodic renewal rather than a permanent measure, so it is worth asking about the expected interval for whatever is applied.
Will waterproofing stop my chimney leak?
Only if water is genuinely soaking through the brick faces. Leaks from a cracked crown, failed flashing or an uncapped flue are entry points that a surface treatment cannot address, and those are the more common causes.
Does waterproofing change how the brick looks?
A proper breathable masonry repellent is designed to be essentially invisible once dry, without gloss or color change. Products that visibly coat or darken the surface are usually the film-forming type to avoid.
When is the best time to apply it?
During dry moderate weather, on masonry that is dry through, with enough time to cure before freezing conditions arrive. That makes late spring through early fall the practical window here.
Does the crown need waterproofing too?
The crown is usually addressed separately with a crown sealer or repair, because it is a horizontal surface taking direct weather and cracks rather than absorbing. Treating the brick while ignoring a cracked crown leaves the main entry point open.
Is waterproofing worth it on an older chimney?
It can be, once the masonry has been repaired and is sound. On an older chimney with receding joints or spalling brick, applying it first would seal the surface of a problem that continues underneath.
Published September 23, 2026