Deck & Patio Cleaning

Wood is soft and grain-directional, and that is the whole reason deck cleaning goes wrong. A pressure washer tears out the soft spring wood between the harder grain lines and leaves a corduroy texture behind. It looks fine wet. Two weeks later it is fuzzy, it holds dirt in every groove, and it hands out splinters. We use a sodium percarbonate wood brightener at low pressure instead. It kills the mildew, lifts the gray oxidation layer, and leaves the grain closed.

The gray itself is not dirt. It is a thin layer of dead wood cells created by UV, sitting on top of perfectly sound board. Take it off chemically and the wood underneath is the color you remember. Take it off with pressure and you take good wood with it.

Different decking wants different handling. Pressure-treated pine is the most common out here and the most dramatic to clean. Cedar carries natural oils that give it rot resistance, so it gets a cleaner that will not strip them. Ipe and other tropical hardwoods are dense and oily and get the highest care and a dedicated formulation. Composite is its own thing entirely: the mold on a Trex or TimberTech board grows on the surface film rather than in the material, so it lifts easily, but the wrong detergent will haze the cap layer and that damage is permanent.

Two problems are specific to decks under trees, which out here is most of them. Leaves left sitting over winter leach tannin and leave black blotches that people mistake for rot. And moss on north-facing steps is a genuine slip hazard by March, more than it is an appearance issue. Both come off, but the tannin needs dwell time rather than force.

Stone and pavers are the opposite problem: grime ground into a hard surface. The risk there is not fuzzing, it is joint sand. Blast a paver patio and you wash the sand out of the joints, which is what lets pavers shift and weeds come through the following spring. We run a surface cleaner at reduced pressure and check the joints afterward. Bluestone and flagstone are sedimentary and will spall under a concentrated tip, so those get soft washed. And if you have a white haze on stone or pavers, that is efflorescence, mineral salts migrating up from below, and it is not a cleaning failure. It needs a different product than soap.

Stamped concrete has one trap worth knowing. It is almost always sealed, and the color is in the sealer. High pressure takes the sealer off and the color goes with it. Stamped surfaces get a surface cleaner at low pressure and nothing more aggressive.