When most people think about cleaning a deck, they picture a pressure washer blasting years of grime off wood. And while pressure washing is a key part of professional deck restoration, using it incorrectly is one of the most common causes of premature deck damage we see. The alternative — soft washing — is often the smarter first step. Here's how professionals approach this decision.
What Is Pressure Washing?
Pressure washing uses high-pressure water (typically 800–3,000+ PSI depending on the machine) to mechanically remove dirt, stain, mold and weathered surface material from wood. At the right pressure, it's highly effective. At too high a pressure, it raises the grain, splinters the surface, drives water deep into the wood and can structurally damage softer wood species.
For most residential deck wood (pressure-treated pine, cedar, SPF), professional deck crews use 800–1,200 PSI with a fan tip nozzle (25° or 40°). Going above 1,500 PSI on softwood risks visible damage — the grain will raise and the surface will feel rough even after drying. Going above 2,000 PSI can physically erode the wood surface.
What Is Soft Washing?
Soft washing uses low pressure (typically 100–500 PSI — about the pressure of a garden hose on a high setting) combined with specialized cleaning solutions to do the work chemically rather than mechanically. The chemistry handles the heavy lifting:
- Sodium percarbonate or oxygen bleach — breaks down mold, algae and mildew at the cellular level without damaging wood
- Wood brighteners (oxalic acid) — neutralize tannin stains and restore a fresh, even colour to weathered grey wood
- Surfactants — help the cleaning solutions penetrate deeply into the wood grain and lift out embedded dirt
The solution dwells on the surface for 10–20 minutes before being rinsed with low pressure. No grain raising. No splintering. Just chemistry doing what brute force can't.
How Professionals Use Both Methods
The best deck cleaning combines both approaches, and the sequence matters:
- Pre-wet the deck with plain water to prevent the cleaner from drying too fast in sun
- Apply the soft wash cleaning solution and allow it to dwell — this is where most of the actual cleaning happens
- Agitate stubborn areas with a stiff brush if needed
- Rinse with low-to-moderate pressure (800–1,000 PSI) to remove the solution and loosened debris — working with the grain, not across it
- Apply wood brightener if the wood is significantly weathered to restore its natural colour
- Final rinse and allow to dry completely before sanding or staining
Using this combined method, we can clean a deck more thoroughly than high-pressure washing alone — with zero grain damage.
The DIY Pressure Washer Problem
Consumer pressure washers from hardware stores often run at 1,500–2,500+ PSI and come with narrow-angle nozzles that concentrate the pressure. Many homeowners use these on their decks at full pressure with a 0° or 15° tip — which can visibly streak and fuzz the wood surface in a single pass.
The damage looks like this after drying:
- Raised grain (rough, fuzzy surface texture)
- Streaks running with the grain direction
- Visible "cleaning lines" where passes overlapped
- Lighter coloured patches where surface wood was removed
This damage doesn't mean the deck is ruined — it usually can be sanded smooth — but it adds time and cost to the restoration process. Prevention is simpler: use a wide-angle tip (25° or 40°), stay at least 12 inches from the surface and move continuously to avoid dwelling in one spot.
Special Cases: When Soft Washing Is Mandatory
Certain situations call for soft washing exclusively, with minimal or no pressure:
- Older, weathered cedar — cedar gets softer as it ages and can be significantly damaged by high pressure
- Composite decking — most composite manufacturers specify maximum 1,000–1,500 PSI from at least 8–12 inches away; some composite systems require soft washing only
- Decks with existing failing stain — high pressure over peeling stain makes a bigger mess, spreading fragments across the deck and into crevices
- Painted decks — if you're trying to preserve the existing paint, soft washing is the only safe cleaning option
The Bottom Line
Effective deck cleaning isn't about using the most pressure — it's about using the right combination of chemistry and controlled pressure for the specific wood, finish condition and level of contamination. Professional deck crews dial in these variables for every job. DIY approaches with consumer equipment often use too much pressure and too little chemistry.
If your deck needs a proper clean before restaining, or if it's been years since it had any attention, contact Restore My Deck for a free quote. We handle the full process — clean, sand, repair and stain — with the right tools and the right technique for your specific deck.