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How To: Pressure Wash an Old House

By The Craftsman on Jan 21, 2013

How to Pressure Wash Wood Siding

Using a pressure washer on an old home is not as simple as you might think. While it may be a great way to clean dirty siding and prep for new paint, if not done properly it can cause more harm than good.

You can cause damage to wood or older soft masonry and force water into the structure of your old house.

So to help you prevent this, I put together a quick primer on using a pressure washer properly to protect your biggest investment.

Don’t Get Too Close - This is the number one problem with pressure washing a house. People put the nozzle right against the surface to get those stubborn stains. Inevitably, this will dig out portions of the wood or mortar and ruin perfectly good siding. Stay at least one foot away from the surface at all times.

Pressure Washer Damaged WoodPhoto by Jon Chapman

Photo by Jon Chapman

Use a Lower Strength Washer - Some commercial pressure washers are way too powerful to be used on an old wood house. They may be perfect for cleaning driveways, but they will blast right through wood siding, especially if there is any wood rot. I prefer a 1500 psi pressure washer. Even if I slip up I won’t cause nearly as much damage as a powerful commercial washer.

Keep the Stream Wide - Many pressure washers have an adjustable nozzle that allows you to make the stream of water go from a wide fan all the way down to a single jet stream of water. That jet stream can dig a hole through asphalt! Don’t even think about using it on your house.

Use Vinegar For Mildew - White vinegar is a great cleaner around the house and a natural choice for cleaning mildew off the exterior of your house. Put it in a spray bottle and apply it in small sections. Let it sit about 30 seconds to a minute and then use the pressure washer to rinse it away.

Scrub, Scrub, Scrub - For the really stubborn areas, the best you can do is give up on the pressure washer and use a strong scrub brush with soap and water. Screw one on an extension pole to reach those hard-to-get areas.

Keep Good Aim - If you aren’t careful with your aim, you can shoot pressurized water up under the clapboards or shingles and into the walls. And there are plenty of things inside your walls that don’t react well to pressurized water. Try to wash downward along the natural path that water from rainfall would take.

Let it Dry - Once you’re finished pressure washing, if you plan to paint, make sure you give the house ample time to dry out. Painting wet wood is a great way to waste money on a paint job that won’t last. Depending on your climate, 12 to 24 hours probably isn’t enough. 48 hours is a safer bet, but you’ll never have a problem from waiting too long.

Follow these simple rules and you shouldn’t run into any big surprises when you go back to examine your work.

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