Illustration for Water Repellent on a Brick Chimney

A homeowner in Durham, North Carolina, asked about exactly this on a home forum in June (community discussion). The house sits on a shaded, wooded lot; the chimney crown was cracked, moss was growing near the top, and a salesman added $1,350 to pressure wash and apply water repellent to the brick. The poster said the product carries a 10-year warranty. One reply said the crown was the bigger priority and suggested a gentler chemical wash over pressure. Another said a 5-gallon pail of sealant had cost about $250 for a different job (stamped concrete), and that doing it yourself could save $700 to $800.

What a water repellent does, and doesn’t

The Brick Industry Association’s technical note on clear coatings sets out the limits:

  • A water repellent isn’t necessary for water resistance on brickwork with normal exposure, when it was built and maintained properly.
  • Fix the conditions that let water in before applying any coating.
  • Penetrating repellents seldom stop water through cracks wider than 0.02 inch, and their effect against wind-driven rain is limited.
  • Use only breathable coatings, with a water vapor permeability of 0.98 or more, and consider a siloxane or siloxane/silane blend.

The note warns that with film-forming coatings and repellents below that breathability, salts can get trapped under the coating and damage the brick. That’s why “breathable” is the word to look for on a quote.

What it costs

Job DIY cost Contractor price Notes
Water repellent only 5-gal ChimneySaver Advanced: $268.87 (Copperfield) to $409.99 (Rockford Chimney Supply) $150 to $400 (Dr. Sweep, Detroit area); $200 to $500 (Murphy Masonry blog, Minnesota; a typical range for sweeps’ waterproofing) About 125 sq ft a gallon, per the seller
Waterproofing with prep Not a DIY line $387 to $884 (Seattle Chimney Pros) Includes mortar joint repair before sealing
Crown repair (fix first) Not a DIY line $332 to $995 (Seattle Chimney Pros) Have a pro inspect first

Prices from each company’s own page, checked October 2026. How we research: methodology.

Against those numbers, $1,350 for a wash and repellent is above the repellent-only ranges, though the wash and the unknown scope may explain part of it. Ask for the product name, whether it’s breathable, how it’s applied, what the wash method is, and what the 10-year warranty covers. The forum poster later learned the crew sprays the repellent and wets and tarps the surrounding surfaces first.

Clean before you seal

Cleaning and sealing are separate steps. The brick note warns that stains or salts on brick treated with a clear coating may be difficult or impossible to remove. For brick cleaning, see our guides to black streaks on brick and white haze on brick.

Shade and rain make it more tempting

The forum poster’s lot is shaded and the region humid. Raleigh-Durham averages about 46 inches of rain a year, with about 75 days of 0.10 inch or more, per NOAA’s 1991–2020 normals. The brick note allows that under certain conditions a clear water repellent may be beneficial; ask the contractor which conditions apply to your chimney, once the crown is sound.

Inspect first

Have a chimney or masonry pro inspect the chimney. The Chimney Safety Institute of America follows the NFPA 211 standard, which says chimneys should be inspected at least once a year. For a house with historic brick, see washing a historic house the gentlest way.

Sources

Based on 9 sources · How we price