Soft Washing Cedar Siding: The Right Way to Clean Wood Without Damage

Cedar siding is beautiful, durable, and notoriously easy to damage with improper cleaning. High-pressure washing blasts off the soft grain, forces water into joints, and can cause warping and splitting. But untreated mould, algae, and lichen cause just as much damage over time — darkening the wood, lifting stain, and accelerating rot in shaded areas. Soft washing cedar requires a different approach than vinyl or brick: lower concentrations, careful chemistry, and a wood brightener step that most contractors skip.

Why Cedar Requires a Different Approach

Cedar is a softwood with an open grain structure, which means it absorbs both moisture and chemicals more readily than harder materials. Standard soft washing concentrations used on vinyl or asphalt can bleach the natural tannins out of cedar, leaving it with an uneven grey-white appearance that requires re-staining to correct. The goal with cedar is to remove biological growth without stripping the wood's natural oils, raising the grain, or creating a blotchy colour result.

Cedar also has a natural pH that reacts to highly alkaline or strongly acidic cleaners — both of which can affect how stain adheres later. A professional cleaning a cedar home should understand these chemistry interactions and calibrate their solution accordingly.

The Right Soft Washing Process for Cedar

Step 1 — Pre-wet: Saturate the cedar siding with clean water before applying any cleaning solution. This prevents the dry wood from absorbing solution too aggressively and concentrating chemicals in one spot.

Step 2 — Low-concentration SH solution: Apply sodium hypochlorite at 1–2% (compared to 2–4% for vinyl) with a surfactant, using low-pressure spray equipment. Allow to dwell for 5–10 minutes — shorter than for vinyl siding. Watch for any colour change in the wood that indicates the dwell is sufficient.

Step 3 — Gentle rinse: Rinse thoroughly with low pressure (below 500 PSI) following the grain direction. Work from top to bottom. Avoid spraying directly into joints or overlaps.

Step 4 — Wood brightener (critical): Apply an oxalic acid-based wood brightener after rinsing. This step neutralizes any remaining alkaline residue, restores the natural wood tone, and opens the grain so stain or sealer can penetrate evenly. This is the step most contractors skip — and the step that determines whether the cedar looks like it was properly cleaned or just bleached.

Treating Mould and Lichen on Cedar

Lichen (the hard, crusty grey-green growth common on shaded cedar) is more challenging to remove than soft algae or mould. On cedar, the standard approach is to treat with SH solution, allow the organism to die (which usually takes several days for lichen), then rinse. Attempting to physically scrub or pressure wash live lichen off cedar almost always damages the wood surface. Once dead and dried, lichen releases from cedar more easily with gentle rinsing.

Heavy lichen colonization on cedar may require a follow-up treatment 2–4 weeks after the initial cleaning once the organism has fully died and loosened from the wood surface.

Soft Washing as Prep for Re-Staining

Soft washing cedar before re-staining is one of the most valuable applications of the process. Stain applied over old, mould-contaminated, or organically soiled cedar fails prematurely — the stain bonds to the biofilm rather than the wood. A proper soft wash and brightener treatment before staining extends the life of the new stain by years and produces a more even, professional finish.

D&D Home Services provides cedar siding soft washing with wood brightener treatment across the Kitchener-Waterloo and Cambridge region. Contact us to book a free estimate, whether for maintenance cleaning or in preparation for re-staining.

D&D Home Services Team Exterior Cleaning Experts — Kitchener-Waterloo

With years of hands-on experience cleaning hundreds of homes across Kitchener, Waterloo, Cambridge, and Guelph, our team shares practical, locally-relevant advice you can trust.