A. James Benney responds: Pressure-washing is a good way to remove dirt and loose paint, but you must use the pressure-washer carefully. Add a mild degreaser such as TSP to the water, and wait a day or two for the walls to dry out before applying paint. Many modern latex paints actually allow moisture to breathe out through their dried film. If using oil paints or stains, let the surface dry for an extra day or two before application. The same holds true for decks.
Remember that it is easy to do a lot of damage in a hurry with a pressure-washer, especially to wood siding and decks. Improperly handled, a pressure-washer can gouge soft wood, drive water into the interior of buildings (staining walls and ceilings), break glass windows and light fixtures, and injure the operator or someone nearby.
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