how to pressure wash house before painting
Answers
A pressure washer is one of the best time-saving tools to come along in years. Its high-velocity water spray cleans dirt, grime and chalking paint from otherwise sound painted surfaces. Pros like pressure washers not only because they're fast, but because they scour the old paint so the new coat will adhere better. It definitely beats the old garden hose, scrub brush and TSP cleaning method, a task so slow that many people just skip it.
In this story, we'll show you how to pressure wash your home effectively and safely, from start to finish, without ruining the siding or compromising the future paint job. If you're lucky and your paint is sound (no peeling), pressure washing may be the only prep work needed.
A pressure washer excels at scouring away dirt, grime and especially chalking, the powdery pigment left on the surface when old oil and some latex paints deteriorate. The scouring action is so strong that you won't need a cleanser (TSP or non-phosphate substitute) like you would if you washed the surface by hand.First off, look for dirt, especially up under the soffits. And then rub the paint surface to check for chalking. If the previous coating was 100-percent acrylic latex paint, it probably won't chalk. If the painted surface is clean and not chalking, pressure washing is optional. But most pros do it anyway to make sure the new paint will adhere well.
The high-pressure stream of water will blast away loose paint too, but resist the temptation to use it as a paint removal tool. The high pressure can easily gouge wood siding or knock the mortar from between bricks. Besides, the pressure washer can't do a complete scraping job. You'll have to scrape off additional paint anyway, so you won't save much time.
Pressure washing works on wood, vinyl, aluminum siding and masonry, but due to its high pressure, we don't recommend it for hardboard siding. Hardboard is more vulnerable to moisture than wood and it's extremely difficult to repair if you accidentally gouge it.
Pressure washing won't stop mildew. (It'll wash most of it away, but the mildew will soon grow back.) Mildew resembles a dirty-looking blackened area. To identify it, apply a little bleach. If the black spots disappear, you have mildew. Using a scrub brush instead of the pressure washer, wash the area with a mixture of 1 part bleach to 9 parts water. If the bleach test had no effect on the black spots, they're dirt and you can pressure wash them away.
Warning: Pressure washing is not a safe paint prep method if the exterior paint contains lead. If your home was built before 1978 (when lead paint for residential housing was banned) or if you're unsure, have your paint tested or contact your local health department for safe handling instructions.