Deck Cleaning

Our cleaning process goes well beyond pointing a pressure washer at the boards. We assess the wood species, the extent of biological growth (mildew vs. algae vs. lichen are handled differently), the condition of the existing finish, and whether the deck has any soft or checked boards that need flagging before cleaning begins. From there we select the appropriate combination of soft-wash detergent, pressure, and tip angle to clean without damaging wood fibre. Soft species like cedar and older pine can have surface fibres shredded by a high-pressure tip held too close — that leaves the wood looking 'fuzzy' and requires sanding to correct. We've seen it on plenty of DIY jobs, and we avoid it entirely.

Soft-washing uses a low-pressure application of cleaning solution — typically a sodium hypochlorite blend with surfactants and sometimes an oxygen bleach component — that kills biological growth at the root rather than just blasting the surface grey. It's the preferred method for decks with established mildew or algae because pressure alone tends to smear biological material into the grain rather than eliminating it. The solution dwells on the surface for 10 to 15 minutes, doing the actual cleaning work, then is rinsed off at low pressure. The result is a genuinely clean surface, not a pressure-scoured one.

Pressure washing is appropriate for heavier contamination — caked mud from landscaping work, embedded grit on horizontal surfaces, old failing solid-colour stain that needs mechanical help to release. The key variables are PSI (we typically work in the 1,200 to 1,800 PSI range for deck boards), tip angle (25-degree minimum on soft wood), and distance from the surface (never closer than 8 to 10 inches on cedar). Hardwoods like ipe and tigerwood tolerate higher pressure and narrower tips. We adjust for the specific wood species on every job.

After washing, a wood deck is clean but not necessarily ready for stain. Washing raises the pH of the wood surface and, especially on older decks, the grey tannin oxidation remains even after the biological material is removed. A wood brightener — oxalic acid or a citric-acid blend — is applied wet-on-wet after the wash rinse. It drops the pH back to neutral, chelates the iron tannins that cause greying, and physically opens the wood grain. You can see the transformation in real time: the boards go from dull, weathered grey to a warm, honey-toned wood colour as the brightener activates.

Skipping the brightener is one of the most common shortcuts in the industry. The visible result looks fine when the stain goes on, but the stain isn't penetrating into open, neutral-pH wood — it's sitting on a slightly closed, high-pH surface, and the adhesion suffers. On weathered cedar in London's humid summers, skipping the brightener also leaves dormant mildew spores in the grain that reactivate under the new stain layer. We include brightening as a standard part of every deck clean that will be followed by staining.

Not every deck cleaning job is a precursor to staining. Some clients have a relatively new, properly stained deck that just needs a thorough annual clean to remove the mould and pollen that build up over an Ontario summer. Others have a composite deck that doesn't need staining but has developed the green algae film that composite surfaces are prone to in shaded areas. And some homeowners simply want the deck looking sharp before a summer event without committing to a full stain project right now. All of those are jobs we handle as standalone cleans.

For annual maintenance washes, we use a gentler detergent mix without the aggressive sodium hypochlorite concentration required for heavy infestations — enough to kill and remove surface biological growth without stressing the existing stain. We also check the deck surface condition during every clean and flag anything that needs attention: loose boards, fasteners backing out, joist peeking through where boards have shrunk, or areas where the stain has worn through. A short maintenance visit once a year in the London area often prevents a much larger job down the road.