House Exterior Cleaning - Pressure Wash Services

As I mentioned on a recent post regarding roof maintenance, this is the time of year that I see contractors come out of the wood work with their pressure washers unleashing havoc on unsuspecting home owners.

Many contractors offer services to pressure wash the exterior walls on homes. This is especially prevalent on stucco homes. In the worst case scenario, the contractor will even add a soap dispenser to the gun.

Pressure washing any building component is usually a bad idea. You are blowing water at high pressure at surfaces that are not water proof. This water often migrates below the cladding's surface where it can become trapped for weeks or even months in the wall assembly. The water will often migrate to large areas behind the cladding utilizing capillary action (water can travel in all directions when a small gap/crack is present). This trapped moisture can then start to deteriorate the building paper or wrap, change the properties of the paper or wrap (once these materials are wet for over an hour, they loose most of their ability to shed water - no protection during next rain storm). These actions then can lead to the underlying structure (Plywood/OSB sheathing) getting wet and starting to deteriorate. A secondary problem is that any part of the wall assembly that has been previously saturated tends to attract water in the future (even if it has completely dried out) lowering its defence during subsequent rain events. Finally, just the pressure itself can lead to mechanical damage of the wall components.

Adding soap to the mix really escalates the problems. Soap contains surfactants. These surfactants change the molecular makeup of building papers and wraps substantially reducing their effectiveness to shed water (on a permanent basis). You have now compromised the buildings sole defence against water ingress (the cladding is only considered a water shedding surface not a water resistant surface).

Most wall cladding can be cleaned with a simple brush and low pressure garden hose. For stucco, you might want to try specific cleaners formulated for this application. They are sprayed on, allowed to soak for minutes/hours and then rinsed off. You may also benefit from one of those car washing wands that attach to a garden hose and have a spinning head. Just stay away from the pressure washer. This includes trying to remove loose paint prior to re-painting. You will often create the problems mentioned above and the wood surfaces are often still wet (on the underside surface) when the cladding is re-painted leading to a paint job that will not last as blister form as the trapped moisture evaporates in the sun and causes a vapour bubble to form below the paint's surface.

Do not be duped by these contractors. Do your research and get informed. Say no thanks to any contractor who offers to pressure wash any part of your home's exterior.