Masonry Magazine July 2006 Page. 43
Pressure Washing Advice
Some people think pressure washing is a small pressure washer but it isn't-it's a bull's-eye pressure water concept, which can damage severely. There are articles written where guys have just totally destroyed buildings using these systems. If you get a good unit, they come with a set of nozzles: 15, 25 and 40 degree. My suggestions are always start with the 25-40 degree fan tips with 1,000 psi or less and five gallons a minute.
Taking a different tack is Weil. "High pressure water alone doesn't compare to the results of a hot chemical/water mixture. The chemical is activated by the heat - for every 35 degrees the acid temperature is increased, it becomes twice as active. The chemical does the work without damaging the brick face. Without using a chemical, one is depending on erosion for cleaning. In comparison, erosion will either leave mortar residual or, if the operator keeps blasting water, the risk of damage to brick face, mortar joints or both increases dramatically. The Kem-O-Kleen washer provides the operator with heated high pressure water for initial wet-down and final rinse, chemical-water mixture for cleaning, and hot water for the final rinse."
Since Prosoco makes a line of cleaning solutions, Henry's next comment is expected. "What we recommend is using a good proprietary masonry cleaner that's going to do most of the work of getting the stuff off the wall for you. Then you don't have to use super high pressure that can damage the masonry and joints. We recommend no higher than 1,000 psi to rinse down a cleaned masonry wall. Anything more than that and you take a chance of putting marks on that wall and harming the joint."
He added: "It's not commonly known but it's not really the pressure that does the work for you, but the amount of water you put on the wall. We recommend pressure washing equipment that is going to allow you to put six to eight gallons per minute on that wall. If you do that you are going to thoroughly flush that wall of any residues, dissolved contaminants and spent cleaners, and you are going to get great looking results."
That covers the new work aspects of cleaning. What about restoration? "On restoration jobs it's probably more important than ever to control your psi with the pressure wash," Henry said. "That masonry is often even more sensitive than your new brick and block. On new brick and block, we can pretty much make a blanket recommendation of between 500-1,000 psi, six to eight gallons per minute. On a restoration job every one of those is going to be a little different. As a general rule you want to use a lot of water and limit your psi, but you also want to test before you do anything. And you always want to error on the side of caution. You really don't want to error at all."
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