Cleaning concrete is every new contractor’s favorite place to start. The work is relatively easy (with the right tools and cleaners and sealers) and relatively free of pitfalls.
Soft-wash techniques for cleaning concrete are not necessary since the surface of cured concrete can withstand thousands of PSI of pressure. Therefore, most contractors use a direct-wash method. The direct-washing of concrete can be done with a standard wand and nozzle, with a turbo-nozzle, or with a surface cleaner. Let’s look at the relative efficiency of each of these methods:
Washing with a typical fan nozzle, usually a 25-degree (green) nozzle, takes the longest amount of time. Using this method, it frequently takes 2-3 hours to fully clean a typical 1200-square-foot driveway. Spots are easily missed that don’t show up until the driveway actually starts to dry.
Washing with a turbo-nozzle is much more efficient because of the width of the path it cleans and because you effectively hit each area twice in every pass – making it highly unlikely that you miss any spot. Washing a typical driveway with a turbo nozzle usually takes about 1 to 2 hours to do.
Washing with a surface cleaner is easily the fastest and most efficient method. Your cleaning path will probably be 18” to 30” wide (depending on your equipment). The time to clean a typical driveway with a surface cleaner is often well under one hour. This is the most efficient method to use. The cost of purchasing a high-quality surface cleaner is less than $1000 and often will pay for itself well before the 10th driveway. Not buying one of these is usually a bad business decision.
Don’t be fooled into believing that “the larger the surface cleaner, the faster I will get the job done”, however. In fact, your pressure washer’s cleaning power determines your speed. If you buy too large a surface cleaner, you will have to move it very, very slowly. If you buy a small surface cleaner, you will be able to move quickly across the surface. As a rule of thumb, with 4 GPM equipment you must stick to a two-arm (a.k.a. two nozzle) surface cleaner. You are most efficient staying in the 18” to 21” diameter range.
The direct-wash method is open to using either the dwell method or the injection method. With the dwell method, you apply the cleaner at the proper concentration. Let it sit on the surface for about ten minutes or so and then begin washing. With the injection method, you downstream the cleaner through your equipment. The injection method sometimes uses a little more cleaner but saves you a little time. Some contractors use one method while others use the other method. It comes down to personal choice.
In either method, it is common to scrape excessive old oil from the surface and pre-treat spots before beginning the wash.