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Pressure Wash House Before Painting

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Pressure Wash House Before Painting
Pressure Washing Before Painting Graphic
(c) Lee Wallender; Licensed to About.com
Before painting your house exterior, you must clean the siding. Don't think you can skip this step, either. The minute you start washing it and seeing all of that pitch-black water coursing off, you'll be glad you did that.

To Clean or Not to Clean?

I won't preach too many homilies about the value of cleaning before painting, the main one being that clean siding means your exterior paint will last longer. Contrary to what paint manufacturers say, the world will not immediately end if you don't clean before painting. The paint will apply fine, it will adhere; it will look good. It just won't last. By painting dirty siding, you seriously shorten your paint's lifespan. Considering how hard and expensive it is to paint house exteriors, it's a good idea to get it right the first time. Myself, I would rather paint my house every 7 years instead of every 3 or 4 years. I will invest the extra time in thoroughly cleaning the siding to boost the lifespan.

Manual Cleaning vs. Pressure Washing

In another article, I advocated cleaning your house by hand prior to painting. I still think this is the best way.

Have you ever used a touchless car wash? Then you'll know that washing without physical contact produces just-adequate results, but never great. After a touchless wash, you can wipe a white cloth across the vehicle and pick up dirt.

It's the same with cleaning your exterior. Manual makes for cleaner siding. But we've got to be realistic: it's incredibly hard and time-consuming to wash an entire house by hand.

Your Tools

  • Pressure Washer: Washers come in gas- or electric-powered models. Since you want to treat your siding gently, you won't need a high-powered washer; electric will suffice. However, if you have a two-story house, the high-volume gas pressure washers fitted with special nozzles will allow you to clean the upper areas--all while standing on flat ground.
  • Cleaning Solution: Purchase solution made for pressure washers, and specifically for house siding. Never use bleach or bleach-based solutions, as they may damage the pressure washer.

Wash, Not Strip

The point of pressure washing your house siding prior to painting is to wash it, not to strip paint. True, most pressure washers are strong enough to take off paint. But stripping should be a separate step done with a scraper, sander, and heat gun, after the process of washing.

Besides the dangers (listed below), pressure washing simply isn't the most effective way to strip paint. For one thing, in order to remove the paint, you need to inundate the base surface with massive amounts of water. If you have wood siding, you want to minimize raw wood's contact with water.

Etching and Injecting

Pressure washing siding gets a bad name because of these two, very real dangers:
  • Etching: Under certain conditions, pressure washers can cut into concrete and brick. Can you imagine the effect on your cedar, vinyl, or even fiber-cement siding? Disastrous. But this is easy to avoid. First, stand well back. Depending on your washer's psi, this might mean anywhere from two feet to two yards away. Second, ensure that the spray is not set on "stream" at close ranges. This needle-sharp spray can rip lines into siding.
  • Injecting: Be careful of spraying at low angles under siding. The high pressure can drive water deep below the siding. Also watch out for other openings: heating exhausts; vents in the attic or crawlspace; even around windows and doors (their seals may not stand up against the high pressure).

3 Steps to Pressure-Washing Before Painting

  1. Knock Off the Big Gunk: Work from the top down without any cleaning solution. Your intention is only to knock down the big gunk: spider nests, inactive wasp nests, leaves, and the majority of the dirt.
  2. Clean With Solution: Let dry and then do this step when the siding is not in direct sunlight. Next, fill up your pressure washer's tank with the cleaning solution. Spray with the water-solution mixture from the bottom upward. Let soak for about ten minutes. Rinse with fresh water from the top down.
  3. Second Fresh Water Spray: If a couple of weeks pass before you can get to painting, I advise an additional spray-down with fresh water. It's surprising how fast spiders can move in after a cleaning.
Let dry 48 hours before painting or until any bare wood is 100% dry.

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