Choosing the right masonry pressure washer

Words: Daniel AbitboulNot unlike a hammer or wrench, a pressure washer is a universal tool applicable across a range of service fields. Pressure washers can tackle the relatively light job of cleaning vinyl siding, up to the tough removal of caked-on mud or grease from heavy equipment. Not to mention, they can erase centuries of grime from brick buildings, concrete pillars and other stonework.

Pressure washers are purpose-built machines. If you choose an underpowered product, the results will be disappointing, yet going too large adds inconvenience and extra cost. Not to mention, a risk of damaging property.

It takes an understanding of the machine, the application and the cleaning process to determine what type of pressure washer is needed.

Hot or cold?

Two basic types of pressure washers are available — hot or cold — the latter of which is the most popular. They’re compact and economical, and they’ll do the trick for a large number of cleaning jobs. Generally, cold-water units are best at washing away dirt and mud. That covers a lot of applications, including cleaning concrete.

Where cold water falls short, however, is removing grease or grime (dirt that is ingrained or clinging to a surface). A cold pressure washer may push these substances around, but that’s it.

In this case, a hot pressure washer is usually a better choice. Hot water cuts through grease, loosening it from the surface before washing it away. They’re also useful for cleaning when outside temperatures are too cool for cold water. However, the U.S. General Services Administration (GSA) recommends water temperatures not exceed 160 degrees Fahrenheit for masonry applications.

The chemical equation

Using cleaning chemicals can enhance the performance of hot or cold pressure washers. Hot-water pressure washers with additional alkaline cleaners are effective when removing paint, grease or oil from masonry. Hot water is not effective in conjunction with acidic masonry cleaners, however, and using temperatures that are too hot with some chemicals can actually cause surface discolorations or streaking.

The GSA also recommends that high pressures not be used for applying cleaning compounds to masonry. Low-pressure spray equipment of 50 psi or less is preferred to completely rinse and remove cleaning compounds. If too high of pressure is used, trace cleaning compounds can be left behind, resulting in severe remedial problems and staining.

Powered preference

Both hot and cold pressure washers are available with electric motors or gas-powered engines. This decision is largely based on where the machine will be used. If operated outdoors without adequate electrical sources nearby, a gas-powered unit is preferred. Otherwise, many people choose electric motors for the cost efficiency, low maintenance and quiet operation. Keep in mind that many of the higher powered electric pressure washers require a 230-volt, three-phase power source, which isn’t readily available everywhere.

If selecting a hot pressure washer, one must also choose from three options for heating the water: oil-fired, gas-fired or electric. The most likely choice for masonry work is oil fired, which can use diesel, fuel oil or kerosene to heat the water. These units are highly portable, and the fuels are affordable and easily accessible.

After deciding on the type of pressure washer, one must determine what specifications will best meet his needs. Pressure, volume and horsepower ratings are often misunderstood, but they play a large role in the performance of a pressure washer.

Under pressure

Start by considering pressure, which simply helps break the bond between the contaminant and surface being cleaned. Pressure that is too low means the bond won’t break without extra help from hot water or detergents. If pressure is too high, the dirt will blow around more, and the spray may even damage the surface.

Most masonry-cleaning contractors prefer pressure washers that can be adjusted from 500 to 2,000 psi. Pressures between 1,000 and 2,000 psi typically are used for preparation cleaning, however most masonry cleaning ratings range from 500 to 1,000 psi. The GSA cautions using high-pressure cleaning on older or delicate surfaces, suggesting instead medium- or low-pressure cleaning that ranges from 800 to as low as 100 psi.

Go with the flow

Volume in gallons per minute (gpm) equally affects cleaning performance. After the pressure has broken the contaminant-surface bond, the contaminant must be washed away. The greater the flow of water, the more easily the substance rinses clean.

The GSA recommends higher volume pumps for masonry cleaning, because they allow flexibility in adjusting the water pressure as necessary. They also provide a flow that is strong enough to thoroughly rinse dirt and cleaner residue from a surface.

Horsepower and nozzles

Then there’s the matter of horsepower, which determines how much pressure and volume a pressure washer can produce. For example, a 3,000-psi, four-gpm unit requires at least an 11-horsepower gas engine to achieve those outputs. Anything less than 11 horsepower will deliver less pressure and volume than the pump’s actual rating.

Basic formulas can be used to calculate the minimum horsepower requirements of a machine. Note that electric-powered units use a different equation than gas-powered:

Electric motor horsepower requirement: (PSI x GPM)/1460
Gas engine horsepower requirement: (PSI x GPM)/1100

Another way to look at the pressure and flow ratings is through cleaning units. This factors into both psi and gpm to help compare the cleaning power of pressure washers. To come up with this number, simply multiply the pressure and volume specifications. For instance, a 3,500-psi, 3.8-gpm machine would have 13,300 cleaning units, while a 3,000-psi, 4.5-gpm unit would have 13,500 cleaning units. In this scenario, the second unit would offer higher performance.

Finally, there is the matter of the size and type of spray nozzle. For masonry work, a fan-type nozzle with a 15- to 40-degree fan is preferred. Laser tips, O-tips or any fan spray narrower than 15 degrees should not be used on masonry, as these types of tips generate a concentrated stream of water that can damage concrete, brick and similar stone surfaces.

Complete package

Reliability also plays an important role. Before deciding on a pressure washer, carefully inspect the unit. Thick steel frames, a quality engine or electric motor, and ceramic plunger pumps are all signs of a quality machine designed to run for thousands of hours.

The guidelines for picking a pressure washer aren’t complicated, but they’re important. That’s because your money may be wasted if you spend it on an inadequate unit that does a poor job.

Even worse, the cleaning project could end up costing much more than anticipated if you damage a surface with an oversized pressure washer. In the end, learning these guidelines will be well worth the time. And getting the job done right will be well worth the investment.
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