Can You Power Wash a Slate Roof?

Removing moss from your roof will dramatically improve the look of your home. When left on slate tiles, moss and lichens can cause them to become porous and hold onto moisture. Over time, this can cause the slate to look and feel less smooth.

When moss builds up on a driveway, a quick power wash will fix the problem. But can you power wash a slate roof?

Unfortunately, the simple answer to that is no.

You should never power wash a slate roof. While power washing is ideal for concrete surfaces, slate tiles are too delicate to be blasted with a power washer. To avoid damaging your roof, it’s better to use an alternative cleaning method.

How Should You Wash a Slate Roof?

The best way to clean a slate roof depends on the debris build-up. In most cases, it’s best to remove the bulk of the moss and debris by hand using a scraping tool and then apply a nonaggressive treatment to the tiles to kill the biofilm.

The treatment will continue to work over a few weeks, with the weather helping out. While the results aren’t immediate, the tiles will start to self-cleanse once the treatment has started working. Not only is this method less harsh than pressure washing, but it also protects the tiles from regrowth for many years to come.

Why Should I Remove Moss?

To keep your slate roof looking and working great, you need to clean it regularly. When moss is left on the roof, it acts like a sponge holding onto moisture. Not only can this stain your tiles, but it can also lead to the tiles splitting during the winter when the moisture freezes over.

Slate is a sedimentary rock with thin layers that split easily. This quality is what makes slate a suitable roofing material. When used on a roof, the rock absorbs water and can naturally de-laminate during the freeze and thaw cycles of colder months.

When cared for correctly, a slate roof can last a lifetime. A properly laid slate roof will have high-quality flashing and fasteners that don’t fail before the tiles need replacing.

Slate roofs are known as hundred-year-roofs and have the potential to outlive their owners when appropriately maintained. Despite having the potential to last a lifetime, a slate roof is also very delicate. Understanding both the fragility and toughness of your roof will help you learn how to care for it.

Maintaining a Slate Roof

To maintain your slate roof, you should have it inspected every year after the winter. This inspection will help catch issues early to avoid big problems and repair costs in the future. When the weather is cold, the last thing you want to do is get up on a ladder and inspect the roof yourself. To avoid the hassle and ensure a thorough inspection, employ a professional to inspect your slate roof.

When a slate roof is damaged, it may not be obvious unless you know what you’re looking for. If you try to inspect the roof yourself, the first you know of the damage might be when water leaks into your house. To avoid this, hire a slate roofing company that specializes in maintaining slate tiles.

After winter each year, hire them to come out and take a look. Ask them to take photos and write notes about any damage so you have a reference. This way, you can keep an eye on any issues and have them fixed when necessary.

Cleaning a Slate Roof

A dormer window with slate tiles

To clean a slate roof, the easiest option is to hire a professional. However, it’s possible to clean the roof yourself if you want to save some dollars. When cleaning your slate roof, use a medium roughness brush with a regular household cleaner. Be gentle and make sure to wash away the soapy water once you’ve finished.

Never use a power washer or any harsh industrial cleaners as they can cause damage to the slate. It’s also worth noting that you can damage a slate roof by walking on it. If you absolutely have to walk on the roof, make sure you’re wearing soft-soled shoes.


For a thorough clean, check what sort of slate is used on your roof and how it is best cleaned. Natural slates require a different technique to artificial slate, so it’s important to check which you have before getting started.

During your roof inspection, make sure that the underlying roof is checked as well as the slate tiles. The underlying roof must be totally waterproof before you start cleaning, or you may cause water to leak into your home. The connection with the roof gutter must also be good before starting the cleaning process.


After the inspection, you can start on the cleaning process. The best way to clean the roof depends on the type of slate and the level of debris. For most roofs, you should first spray a biological cleaning solution onto the slate and leave it to soak.

Once the product is absorbed, rinse it off with clean water. If you hire a professional, they do this using a special accessory that sprays downwards. This way, the water cannot get underneath the tiles.


Once the roof has been cleaned, it’s time to disinfect the slate. By doing this, the remaining mold spores are killed, and the moss takes longer to regrow.


When the roof has been cleaned and disinfected, it’s advisable to have it coated. However, this is only necessary for artificial slate. Over the years, the protective topcoat of artificial slate wears off. By treating it with a coating it won’t become dirty again.

So, can you power wash a slate roof?

Unfortunately, no. However, other cleaning techniques can leave your slate sparkling and protect it for years to come.

Washing Stuff
Login/Register access is temporary disabled