I don’t know if the professor told us at the time, but the National Park Service says the Colorado River gobbled up all that missing rock, transporting it to the ocean in just 6,000,000 years. It did this with just 14.2 pounds of normal atmospheric pressure pushing down on the water flowing over the rock, not 2,400 pounds as many pressure washers produce.
In other words, water just normally flowing over dense hard rock will erode it. Think of how much destructive force is created when you plug in your pressure washer or pull the start cord on its gasoline engine. I witnessed an agonizing example of this destructive force on a trip to Old San Juan, Puerto Rico, in October 2019. Months before, anti-government protesters had spray-painted slogans on many of the buildings.
The governor dispatched workers to remove the paint, and they decided to use a pressure washer. One of the buildings was built using hard oolitic limestone. The operator of the machine removed the paint, but he also eroded the actual stone, permanently etching into the building facade that had been spray-painted. It was hard to stomach, because one would think within a few minutes the operator could see he was damaging the stone itself.
Think of the things in your home that are much softer than hard limestone — the likes of which many of the buildings in Washington, D.C., are made, including the Washington Monument! That oolitic limestone was chosen for a reason: because it’s so long-lasting and gorgeous.
In other words, if you don’t know how to use a pressure washer and aim that cleaning wand at your wood deck, railing or steps, in a matter of seconds you’ll transform smooth treated lumber into a weathered fishing pier where the soft springwood in between the darker bands of summerwood has been worn away.
Do you use your pressure washer to clean your brick paver driveway, sidewalk or patio? I’m talking about the interlocking bricks made from concrete that have dry pigments added to them. These pavers can be had in an assortment of earthy colors and tones.
That color you see at the surface is just an ultrathin coating of cement paste that has the dry pigments in it. It’s child’s play for your pressure washer to blast away this thin film of color, exposing the actual color of the small stones used to make the concrete. Put the spray wand too close to the brick and you’ll actually blast away some of the small, fine sand used to make the brick.
I see professionals improperly use pressure washers all the time. Many are painters who use them to wash the outside of a house before applying a fresh coat of paint. All too often I see the operator aiming the cleaning wand up to clean things above his head or shoulders. This is a huge mistake.
We builders construct homes thinking about how rain falls. Rain falls down, and in rare instances it can hit a structure sideways during a powerful storm, nor’easter or hurricane. But Mother Nature rarely has rain blowing up to the sky.
Builders lap siding, trim, flashings and so forth so that the falling water doesn’t get behind the outer skin of your house. An operator aiming a pressure washer up can drive water behind the outer skin of your home in short order. Never aim a pressure washer wand up on the outside of your home.
Is your house covered with vinyl siding? Have you ever paid attention to how the pieces of siding overlap at a joint along a long wall? Don’t ever aim a pressure washer wand so the water lifts the overlapping siding and gets behind the vinyl. The same is true for where the vinyl trim is up against windows and doors. There’s a seam there, and the pressure washer can drive lots of water behind the siding that otherwise shouldn’t be going there.
First and foremost you should read cover-to-cover any manual that comes with your pressure washer. The manufacturer may have all sorts of warnings about how to use the machine with different materials.
At the very least, use your own critical thinking skills. Do experiments. Instead of aiming the pressure wand at a 90-degree angle to the surface you’re cleaning, try 45 degrees or even 10 degrees! If you’re using a high-pressure stream of water to remove flaking paint, it’s best to hold the wand almost parallel with the painted surface. The stream of water will burrow between the paint and the surface and blast it away usually doing little harm to the siding or trim.
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