Last month, our article addressed how constant weather exposure can make your chimney a potential safety hazard. No matter what, all masonry chimney materials, even stone, will suffer deterioration with prolonged contact with water—especially to the freeze and thaw process we experience every winter in the Midwest.

So how can you prevent this water damage and waterproof your chimney?

The main source of water intrusion is driving rain, wind or airflow changes, trees, plants and micro-organisms such as algae. However, there are many chimney components that can help protect against damage or deterioration.

Properly Fitted Chimney Caps

Chimney caps are probably the most inexpensive preventive solution that can help prevent water penetration and damage to the chimney. Chimney caps have long been considered important safety and damage prevention components. Without a properly fitted chimney cap, your fireplace can collect large amounts of snow or rainwater and funnel it directly to the chimney interior. A strong, well-designed cap will even prevent birds and animals from entering and nesting in the chimney. And, caps can prevent sparks from landing on the roof or other nearby combustible material.

But, not all chimney caps waterproof your chimney. Your cap should be constructed of sturdy, durable and corrosion resistant material and easily removable to facilitate inspections or cleanings. Chimney caps can be designed to cover a single flue, multiple flues, a large portion of the chimney or the entire chimney top. While a full coverage cap may be a larger initial investment, it is considered the best investment for long-term protection since it protects the entire chimney crown.

Well-Constructed Chimney Crowns

Chimney crowns are the top component of a masonry chimney that cover and seal the top of the chimney. Poor crown construction is one of the leading causes of chimney deterioration. The overhanging drip edge, directing the run-off away from the chimney, helps prevent erosion of the brick and mortar in the chimney’s vertical surfaces. A proper chimney crown should be constructed of a Portland cement-based mixture and cast or formed so it provides an overhang projecting two inches beyond all sides.

Mortar Joints Repointing

Mortar joints on the exterior of the chimney can also be a dangerous entry point for water. Gaps, missing mortar or a shape that does not direct water out of the joints will allow the mortar to become more absorbent which leads to deterioration. A common repair for deteriorated mortar joints is called repointing. This will give the chimney a much longer life span and often enhances the appearance.

Repair or Preplace Flashing

Flashing, or the seal between the roofing material and the chimney prevents rainwater or snow melt from running down into the living spaces where it can damage ceilings and walls or cause rot in rafters. This chimney component joins two dissimilar materials and allows both the roof and the chimney to expand and contract at their own rates without breaking the waterproof seal. Problematic areas include the base of the chimney, the intersection of the chimney and roof and at the chimney crown.

Install a Cricket

A cricket is a water deflector that directs rainwater away from the chimney. This chimney component is recommended on chimneys more than 30-inches wide and important on steep roofs.

Waterproof Masonry Materials

Like most masonry materials, common brick is like a sponge that absorbs large amounts of water drawing moisture to the chimney’s interior. Defective mortar joints or the use of improper mortar or brick can greatly increase water absorption to the interior of the chimney.

Several products are available to use as waterproofing agents on masonry chimneys. These formulas are 100% vapor permeable and prevent water from entering from the outside. They are also five- to ten-year warranty. Paint or clear sealer should never be used as a waterproofing agent because they will trap water vapors and moisture inside the chimney causing further deterioration.

Always keep in mind that waterproofing is a preventative measure. If specific chimney components damage or deterioration exists, the chimney should be repaired before the waterproofing agent is applied. Also, the exterior of the chimney may need to be cleaned prior to applying the waterproofing agent.