Slate Roof Cleaning & Restoration

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No matter the presentation or cause of your roof’s unsightly appearance, you can trust Pacific Exterior to safely and effectively restore it to its original, natural beauty!

Discoloration is one of the most common problems with slate roofs. Safely treating discoloration and restoring your slate roof to its natural beauty is our specialty.

Bio-contaminants such as mold, mildew, bacteria, algae, lichen and moss can drastically detract from the appearance of your natural slate roof. Depending on what is growing on the surface, you may see discoloration in any variety of colors: brown, green, black, red, or even white. It may present as an overall dingy appearance or in a streaky pattern.

As any qualified slate roofing professional will tell you, Extreme care must be taken when working with slate. Even though it is a type of stone, slate can very easily be damaged. Your slate roof represents a significant investment in your home or commercial facility. We recommend you leave it to professionals who are experienced in restoring natural slate roofs.

Pacific Exterior is Northern California’s original Non Pressure Roof and exterior cleaning and restoration professionals. We are a building contractor and certified roof inspector with decades of experience. Since 2010 we have dedicated ourselves to effective cleaning and restoration methods. We are founding members of the National Soft Wash Alliance. Our "Safe Wash" approach has been developed over years of experience and proven results.

Our slate roof restoration is highly effective because it is more than a superficial cleaning – it eliminates the problem at the source with a 100% kill rate against bio-contaminants. We confidently guarantee the beautiful results to last for years.

As a general building contractor, we have been family owned and operated for over 16 years. You can trust us to take care of your slate roof as if it were our own.


Delamination is a common issue with natural slate roofs. This problem is increased with the growth of moss as well as mineral and moisture reactions. While this is a natural occurrence, the use of high pressure to power wash slate roofs will highly accelerate the break down of your slate roof and generally delaminate the slate, leading to costly replacement to damaged slate.

Caution: Slate roof manufacturers and experts warn against the use of washing with high-pressure systems, due to increased risk of damage!

Pyrite Staining

If your slate roof has a reddish or rusty stained appearance, it is likely caused by an oxidizing metallic mineral, such as pyrite, pyrrhotite or marcasite. These are naturally occurring stains that emanate from the slate itself and cause staining. This type of discoloration has been deemed by many slate professionals and organizations to be a natural stain that cannot be removed.

Using specialized cleaning products and processes, Pacific Exterior can completely remove or significantly reduce the appearance of these rust-like stains – leaving your roof beautifully clean and restoring the natural color of each natural stone. This restores the desired color variation of your slate roof.


We are NRCIA certified roof inspectors. While performing our cleaning & restoration services, we will alert you to any observed issues with your slate roof with photo documentation. Some issues that are common to slate roofs are...

Cracked, broken or blistered tiles
Misaligned or missing tiles
Delaminated tiles
Failed flashings (i.e. pin holes, open seams, loose or misaligned elements, etc.)
Broken or clogged downspouts

For professional slate roof cleaning and restoration in the Monterey Bay and San Francisco Bay Areas, fill out our online request form or call, Bay Area (650) 687-0895 or Monterey Bay (831) 275-1296.

What Our Clients Say

We are genuine, friendly, professional and absolutely committed to customer satisfaction.

Bob Fitzgerald, Play by play announcer for the Golden State Warriors. Satisfied customer of Pacific Exterior.

“ Pacific Exterior did an incredible job cleaning my clay tile roof.  They were professional, on time, very thorough and I would recommend them for any and all cleaning situations for any home.  Extremely pleased with their work. ”

Bob Fitzgerald

Golden State Warriors TV Play by Play Announcer
P Schumann - Santa Cruz, CA

“Everything looks great. You did an outstanding job, it's really beautiful.”

P. Schumann

Dr. Scott Fross of Menlo Park. A satisfied customer of Pacific Exterior.

Exceptionally detail oriented. I would highly recommend them to anyone seeking this type of work.

Dr Scott Fross

Menlo Park
M Eschen - Santa Cruz, CA

“It's AMAZING! The crew was professional, hard working and went above and beyond. Would highly recommend them to anyone.”

M. Eschen

"Leading experts. Experienced professionals. Passionate ownership."

Frequently Asked Questions

It is easy to see on most homes while the growth is in process; there are dark black streaks, particularly on the north facing roof, though once the algae has fully taken over it is sometimes hard to tell. (It's never too late to remove.) The best place to look to find out if your roof is dirty is below metal roof jacks flashing and sky lights. There you should find lighter colored streaks or patches...that is the original color and that is what your roof will look like after we have completed our service!

Yes. Pressure washing will dislodge the granules from the surface of the shingles and can scar the shingles causing more problems than you started with. Shingle manufacturers make it very clear that no pressure should be used to clean roofs. Although leaving the roof apparently clean looking, pressure washing alone does not kill the algae and the problem quickly returns. Tile roofs are also susceptible to damage from pressure, particularly the glaze finish and color pigment. The typical result is that the tile loses its color and is left far more porous. The new porous surface fosters the regrowth of algae, lichen, and moss. Removing the outer surface of roof tile using pressure also allows moisture to enter the tile which accelerates degradation.

As soon as you notice any signs of the shading or staining. The gloeocapsa magma bacteria is relatively easy to remove. Moss and lichen require much more time and effort. Even after the treatment, a small amount of dead moss will remain, left to decompose over time. The best time to treat a dirty roof is before signs of moss or lichen.

Yes. Cleaning your roof can save you money in more ways than one...

  • First, the algae and fungus that grows can cause premature roof granule loss, and shorten roof shingle life. So you save money because your roof lasts longer
  • Second, when the algae turn your roof black, it becomes less reflective, and it retains heat; If you use an air conditioner it has to work harder to overcome the increased heat load, costing money in electric bills.
  • Third, the aesthetics of cleaning your roof when it comes to selling your home can not only save you money but can make you money too.

Yes. We have many happy customers who would love to share their roof cleaning experience with you, Most likely, some in your neighborhood. Please feel free to request a list by e-mail.

Yes, we are properly insured and send proof of current insurance out with all proposals. All employees are covered by workers compensation insurance. We are registered with the DIR for governmental work and prevailing wage jobs.

Trusted and Certified

Safe and Environment-Friendly.
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