Cedar Siding, Moss and Mildew: Repainting and Restaining West Coast Homes

Cedar is everywhere on Vancouver homes, from the shingles on a Craftsman bungalow to the board siding and trim on a newer build. It is a beautiful, naturally durable wood, but our mild, damp climate is also exactly what moss, algae and mildew love. If the north side of your house has turned green or grey, or your stain looks blotchy after a few winters, this guide explains what is going on and how we approach restoring and protecting cedar on the West Coast.

Key takeaways

• Moss, algae and mildew thrive on shaded, damp wood. Cleaning them off properly comes before any coating.
• Painted and stained cedar need different maintenance, so decide which look you want before the next refresh.
• Pressure washing too hard can damage cedar fibres. Gentle cleaning and proper drying time matter more.
• Keep wash water and cleaning chemicals out of storm drains.

Why cedar siding goes green on the West Coast

Long, wet winters, frequent cloud and plenty of tall trees mean many walls in Metro Vancouver rarely dry out completely between October and spring. Organic growth takes hold wherever moisture lingers: the north face of the house, walls tucked behind hedges, boards under dripping gutters and the lower courses closest to the ground.

It helps to know what you are looking at:

• Mildew usually shows up as black, grey or green speckles on the surface of paint or stain.
• Algae tends to form a green film, often on shaded walls and fences.
• Moss forms soft green clumps, most often on shingles, sills and horizontal ledges where water and debris collect.

Surface growth is mostly a cosmetic and maintenance issue, but it holds moisture against the wood. Over time that can soften the surface, lift coatings and, in the worst spots, contribute to rot. If boards feel spongy when you press them, they likely need repair or replacement before refinishing.

Painted or stained? Know what you have

The right plan depends on the current finish, so start there.

Painted cedar

Paint forms a film on top of the wood. It hides the grain and can last a long time when the surface is well prepared, but when water gets behind it, paint tends to peel and flake. Repainting usually means scraping loose paint, sanding edges smooth and spot-priming bare wood before the finish coats.

Stained cedar

Penetrating stains soak into the wood instead of forming a thick film. They show off the grain and tend to wear away gradually rather than peel, which makes recoating simpler. The trade-off is that stains usually need refreshing more often than paint, especially on walls that get full sun or heavy weather.

Switching from stain to paint is generally easier than going the other way. Once cedar has been painted, getting back to a natural stained look can mean stripping or replacing boards, so think about the long-term look you want.

How we clean cedar before refinishing

A new coat will not stick well to dirt, chalky old coatings or living growth. Proper cleaning is the step that most affects how long the result lasts.

• Use a cleaner made for the job. Mildew and algae removers and wood cleaners are designed for exterior wood. Follow the label for dilution, dwell time, rinsing and protecting plants.
• Go gentle with pressure. Cedar is a relatively soft wood. A pressure washer set too high or held too close can raise the grain, gouge the surface and drive water deep into the boards. Low pressure and soft brushes do the job without the damage.
• Brush off moss by hand on shingles and ledges before washing, so you are not just pushing it into the gaps.
• Let it dry. Cedar that has just been washed can hold moisture for days in our climate. Coating damp wood is one of the most common causes of early failure, so we wait for the wood to dry out before priming or staining.

Rinse water from cleaning can carry chemicals, paint flakes and debris. The City of Vancouver's bulletin for painting contractors is clear that wash water must not go into street drains or other storm drains, because storm sewers lead to local waterways. Plan where your run-off will go before you start.

Choosing a coating that suits our climate

There is no single best product for every wall, but a few principles help:

• Pick products rated for exterior wood and, where it suits the wall, ones that list mildew resistance on the label.
• Prime bare wood before painting, using a primer suited to cedar. Cedar contains natural extractives that can bleed through some finishes as tan or brown stains, and the right primer helps block them.
• Match the sheen to the job. Ask about sheen when choosing colours, since it affects both appearance and how easily the surface can be cleaned.
• Follow the label for minimum temperatures, recoat times and the time needed before rain. These vary between products.

Keeping growth from coming back

A good finish buys time, but the house still lives in a rainforest climate. Small habits make a big difference:

• Trim trees and shrubs so walls get more air and light.
• Keep gutters and downspouts clear so water does not spill down the siding.
• Keep soil, mulch and firewood away from the bottom courses of siding.
• Rinse off early growth gently each spring before it gets established.
• Touch up scrapes and cracked caulking before water finds its way in.

Frequently asked questions

Can I paint over moss or mildew?

No. Paint or stain applied over growth will not bond properly, and the growth can come back through the new finish. Clean, rinse and dry the surface first.

Should I pressure wash cedar siding?

Only gently, if at all. High pressure can damage the soft surface of cedar and force water into the wood. A suitable cleaner, soft brushing and a low-pressure rinse are usually safer.

How often does stained cedar need recoating?

It varies with the product, the exposure and the colour. Check the manufacturer's guidance and look for fading or water no longer beading on the surface as signs it is time.

What about cedar decks and fences?

The same rules apply: clean off growth, let the wood dry and choose a product rated for horizontal or vertical exterior wood as appropriate. Decks take more wear and usually need more frequent care than siding.

Ready to get started?

Whether your cedar needs a deep clean and fresh stain or a full repaint, we can help you choose the right approach for your home and the West Coast weather. Get your free painting quote from 1-800 PRO PAINTER.

Photo: Zane Lee / Unsplash