Chimney Exterior Cleaning: What It Involves and Why It Matters

The exterior of your chimney is exposed to everything the Pacific Northwest climate throws at it — rain, moss, algae, lichen, and freeze-thaw cycling. Regular exterior cleaning removes biological growth before it causes lasting damage. Here's what the process involves.

What Grows on Chimneys

Moss is the most common and most damaging biological growth on chimneys in Southwest Washington. It retains moisture and physically penetrates masonry with its root system.

Algae appears as green or black streaking on masonry. It's less structurally damaging than moss but indicates sustained moisture on the surface.

Lichen is a combination of algae and fungus. It's more tenacious than moss and more difficult to remove. Lichen roots penetrate deeply into masonry and can cause significant damage over time.

Efflorescence is the white, powdery deposit that appears when water moves through masonry and carries dissolved salts to the surface. It's a sign of water infiltration rather than biological growth, but it often appears alongside moss and algae.

The Cleaning Process

Professional exterior chimney cleaning involves:

1. Assessment: Identifying the type and extent of growth, and checking for existing masonry damage
2. Biocide application: Applying a professional-grade moss and algae killer to the affected areas
3. Dwell time: Allowing the biocide to penetrate and kill the growth
4. Removal: Brushing or low-pressure rinsing to remove dead growth
5. Efflorescence treatment: Applying an efflorescence cleaner if needed
6. Preventive treatment: Applying a treatment to slow regrowth — or consider waterproofing to protect the masonry

What We Don't Do

We don't use high-pressure washing on chimneys. The pressure required to remove stubborn moss can damage mortar joints and force water into the masonry. Low-pressure rinsing combined with effective biocides achieves better results without the risk of damage.