Protecting Chimneys from Water

Structural Damage Caused

by Water Intrusion:

Water is the arch-enemy of mortar, capable of damaging it severely in three significant ways:

(1) By leaching lime: Water draws lime out of mortar, resulting in mortar increasingly porous and unstable.

(2) By chemically reacting with creosote: Uncapped chimneys, cracked crowns, deteriorating mortar and bad flashing allow water into a flue.

The water chemically reacts with creosote to form a highly corrosive acid that begins to crumble cement bonds from the inside, making a chimney increasingly structurally unstable.

(3) Through frost-wedging: Water expands 7% by volume when it is frozen.

If a freeze should occur while porous mortar and brick are water-logged, it can generate enough force to literally pry open cracks in the mortar and push (or “spall”) bricks away from the chimney, and onto the roof & ground below.

Frost-wedging can literally pry apart entire sections of the chimney:

When bricks and mortar are involved, this can mean sections weighing hundreds of pounds:

Of even greater concern, because mortar is necessary to support the thousands of pounds of bricks unstable sandy mortar can risk a structural chimney collapse:

How Do I Make My

Chimney Water-tight?

There are many possible entry points for rain water to make its way into a chimney, so keeping a chimney water-tight requires the concerted “teamwork” of various components, all of which work together and depend upon each other to work properly.

The following are the five primary ways to prevent water intrusion into a chimney:

1. Install a Chimney Cap:

Chimney caps prevent direct water penetration into the chimney flue.

This is the most fundamental thing one can do to protect a chimney from water damage.

Our chimney caps also incorporate a metal mesh that acts as both an animal guard (preventing birds and small mammals from entering and nesting in the chimney, and preventing sparks and embers carried up by draft during a fire from landing on the roof).

2. Build (or repair) a chimney crown: The crown covers the top of the chimney by setting a water-proof slope that redirects water that runs off the rain cap.

A proper chimney crown should be mixed with an elastic (& water resistant) compound such as MascoSeal ®.

3. Flashing: “Flashing” is a metal barrier that prevents water from entering the chimney where it meets the roof.

Proper flashing is actually composed of two elements: “base” flashing and “counter” flashing.

The base flashing is an “L”-shaped piece of metal that presses up tightly against the corner where the roof and chimney meet. The counter-flashing is embedded directly into the chimney right above the base flashing, and is bent downward over base flashing--acting like a mini-umbrella, it directs rain water away from the chimney.

4. Tuck-point:

If the mortar binding the bricks together is weak and porous, it will literally wick water into the flue (through the process called “adhesion”), where it can do serious damage.

This problem can be resolved with tuck-pointing (using a high-speed grinder to grind away 1/2” to 1” into the and mortar separating the bricks, then refilling it with fresh mortar that will resist water and add significantly more structural support).

5. Water Seal: Even carefully-struck mortar bonds and high-quality brick are inherently slightly porous.

For this reason, we use a professional specialized polymer spray-on compound (Siloxane®) to make the brick and mortar on the outside of your chimney water resistant. Think of it as the equivalent of Scotch-Guarding® the outside of your chimney.

And, unlike paint, which accelerates mortar damage by trapping water that has already entered the chimney, our commercial-grade sealant is vapor permeable, meaning that any moisture coming from the inside of the chimney will be able to get out (but not back in).

Our water seal application comes with a 10-year warranty.

Give Yourself Peace of Mind.

Schedule an Appointment Today.

(503) 775 - 3085