Mistake #6: Choosing a Contractor Whom uses Consumer Grade Equipment and Cleaners. Cheap equipment may be a sign of a "fly-by-night" company. Big, high- dollar, skid- mounted pressure washers are not necessary to do a quality job. But, if the contractor uses the same little 2.2 gallon per minute pressure washer that you saw on sale at the home improvement store, you might want to reconsider hiring him. Most quality contractors use 3.5 to 5.5 gallon per minute cold water units for residential use. If a contractor is using consumer grade equipment, he is probably using consumer grade cleaners, also. House, deck, and concrete cleaners, that are sold to consumers, have to be safe to handle, therefore, they are not very concentrated or very effective. Contractor grade cleaners sold through distributors are still environmentally safe but are more concentrated and must be handled with care. Contractor grade cleaners are necessary in order to achieve quality results, without using high pressure, which could lead to damage.