Techniques of Pressure Washing

Mobile Power Pressure Washing:  Tips, Techniques, and Chemical Usage Guide

SUMMARY:  Simply choosing the right pressure washing equipment is only the start. After receiving proper training in how to use it, all the elements must be put together properly for optimum effect. This article provides information on how to get the most out of your pressure washer and equipment.

In this article, you will find advice to help you get the most out of your mobile pressure washer. For further information, contact customer service at at 614-465-6479. Our experienced power wash professionals will be glad to assist you.

Washing Tips and Techniques
Nozzle Selection
Understanding PSI (Pounds per Square Inch)
Wet Sandblasting
Soda Blasting
Painting after Paint Stripping
Stain Removal
Removing Carbon Deposits (smoke) from Engine Exhaust
To Stop Spotting
Cleaning Copper Trim
Spider Webs
Chemical Selection Guide for Products
Mixing Instructions
Car Washing
Pickup and Van washing
Tractor and Trailer Washing
Trailer Decal Removal:
High-Pressure Wax Rinse
Heavy Equipment Washing
Engine Steam Cleaning
Aircraft Washing
Building Fire Damage Washing
House Washing
Boat and Ship Washing
Aluminum Siding Washing
Vent-A-Hoods Washing (Non-Asian Restaurant)
Vent-A-Hoods Washing (Asian Restaurant)
Asphalt Road Washing
Concrete Washing
Asphalt and Tar Removal
Aluminum Trailer Brightening
New Masonry
Paint Stripping
Fabric Awning Cleaning
Vinyl Awning Cleaning
Related Articles

Washing Tips and Techniques

  • Always fog or presoak the surface with a detergent, degreaser, or chemical presoak. Presoaking reduces wash time and chemical cost.
  • Hot water is a better solvent than cold water.
  • Always rinse the detergent off the surface before it dries.
  • Commercial contractors generally use 4 to 6/gpm at 1500 to 3,500/psi for most cleaning applications. An exception to this is wood cleaning. Here 500 to 2,000/psi is preferred with chemical cleaning to reduce the furring of the wood. Water flow rates of less than 4 gallons per minute – found on general consumer (homeowner) units – are not high enough to be competitive because of increased cleaning time, which raises labor costs.
  • Chemical dilution is largely a matter of personal preference. For most mobile power washing work, chemical costs run from three to five percent of gross sales, labor accounts for 30 to 45 percent, and fuel for heat is two to four percent. If chemicals and heat costs are reduced, labor costs increase because of increased work time. A slight increase in chemical and fuel costs actually reduces labor costs, because work time decreases.  Work smarter – soap and heat are cheaper than labor – not harder.
  • Washers with chemical injection before the pump, start out with the metering valve open 1/4 turn. Then adjust as needed.
  • W-200 Spray Wax is similar to spray wax used in coin-operated car washes. Apply the wax hot and follow with a cold rinse for fine surfaces like cars and pickups. On heavier surfaces, like homes and trailers, the cold rinse is not necessary. The application of wax extends the life of the wash job, makes subsequent cleaning easier, and enhances the overall appearance. Note: Because the application of wax will extend the life of a wash job, some contractors choose not to use it because they prefer to wash more often. There are two sides to this. While the use of wax may reduce your income because of the extended life of your cleaning, the enhanced appearance, and extended life may generate more business because of the perceived quality of the work.
  • For fleet washing, wax in the rinse water reduces dirt adhesion and lessens subsequent washing time. In heavy concentrations, wax reduces cement adhesion on concrete trucks.
  • The tips provided in this section will reduce brushing to about five percent of the total workload. Typically, contractors only brush in the spring or the fall, or as needed.
  • Brushing once or twice per year at a specified time allows the contractor to prepare and schedule extra, short-term, help for those designated times.
  • For Environmental Power Washing Techniques read Report 507.

Nozzle Selection
There are two factors that need to be considered when choosing the proper nozzle: the nozzle orifice size and the spray angle. These determine the gallons per minute at a particular pressure of the water flow. To determine a nozzle size you need to know the GPM (gallons per minute) and PSI (pounds per square) necessary for the job you are doing.

When the nozzle size increases, the psi of your pressure washer is reduced while the flow remains the same. By reducing the pressure of your washer with the unloader, you will decrease both the psi and GPM. Knowledgeable contractors reduce the psi of their pressure washers by increasing nozzle size in order to keep the GPM at its maximum.

Choices for spray angle range from zero to 65 degrees. 25-degree angles fit the natural wash pattern of most contract cleaners. However, many contract cleaners prefer a 40-degree spray angle because they can hold the nozzle closer to the surface, obtaining the same width of contact, while at the same time delivering greater impact pressure and higher temperature at the point of contact. It is necessary to keep the nozzle a consistent distance from the surface.

A zero-degree nozzle concentrates all of the cleaning power in a very small area with a high degree of cleaning power at the center of impact. While this provides tremendous power and cleaning ability, it can cause streaking similar to chicken tracks, and sometimes the entire track of the wand’s wash pattern is visible. A zero-degree rotating nozzle like the ST-58 or Rotomax solves this problem. They provide the power of a zero-degree nozzle and the coverage of a fan nozzle and, when used properly, do not leave the wand marks (tracers). Consult our catalog for detailed information on nozzles.

Understanding PSI (Pounds per Square Inch)
Water pressure from the pressure washer is measured in pounds per square inch or psi. This pressure is the amount of force delivered to the surface being cleaned and is the critical factor in breaking debris from that surface. PSI is determined by the orifice size of the nozzle tip and the flow rate (gallons per minute). For labeling purposes, the standard nozzle size for measurement is a #4 orifice, which delivers 4.0/GPM at 4,000psi. As nozzle sizes increase or decrease, psi fluctuates accordingly.  The nozzle chart in our catalog lists the psi with different flow rates and nozzle sizes. Nozzle selection depends on the work, and the amount of pressure a surface can withstand before it is damaged.

While psi is a constant at the tip of the nozzle, the pressure decreases as its distance from the targeted surface increases. Experienced power wash contractors understand how to manipulate these distances to maximize both cleaning power and their time.

Because the pressure that contractors need varies a great deal, they get the most out of their equipment by adjusting the distance between the nozzle and the surface being cleaned. For less pressure and heat in the application, they hold the nozzle back, thereby increasing the distance from the surface. For increased pressure and heat, they hold the nozzle closer. Larger contract cleaners will use pressure washers that produce 4 to 6 GPM at 3,000 to 3500 psi at 200⁰ F for concrete cleaning. Vehicle washing can be accomplished using 1,500 to 2,000 psi.

Heat provides a tremendous advantage when cleaning grease and oil. A few Vent-a-Hood cleaners will use steam heated to 310⁰ F, while others will use units that deliver 3,000psi at 200⁰ F. However, some vent cleaners use electric, 1,000 PSI cold water washers hooked up to hot water (they must hand scrape more for this to be effective).

The psi for decks and other wood surfaces varies from 200 to 3,000 and must be carefully tested first, as too much pressure will cause the wood to fur. If this happens, you will need to sand the affected areas with fine sandpaper or steel wool to knock off the furred surface. Many professional deck cleaners use a variable pressure wand (like the ST-54 36″ Double Lance Wand) so they can adjust the pressure as necessary. Using low pressure, and letting the chemical (like’s DSR-49 Deck and Siding Restorer or DSR-50 Deck and Siding Restorer plus Stripper) do the work helps avoid furring. Test the effect of pressure on the underside of the deck.

Wet Sandblasting
A wet sandblasting attachment for a pressure washer with 4/gpm at 3,000/psi will use fifty pounds of sand for every twenty minutes of continuous use, making it half as effective as commercial air sandblasting unit. As such, the market for wet sandblasting is profitable only for small jobs on which the pressure wash contractor is already working, environmental jobs where wet sandblasting is required, or for some building restoration jobs in areas where chemical cleaning does not work.

Soda Blasting
Baking soda blasting is an environmentally friendly alternative to sandblasting and does not require any clean-up because of the materials used. It is also a milder abrasive that will remove surface material without damaging the underlying materials. There are several industrial applications for this technology, including monument and statue cleaning.
Painting after Paint Stripping

Note: The measurement of whether a surface is acidic or alkaline is a number on the pH scale. The scale runs from one to fourteen, with seven being neutral. Color-coding is also used, with red being the most acidic, deep blue highly alkali, and green neutral. Most paints need to be applied to a neutral surface. As paint strippers are high in pH, it is necessary to neutralize the surface after stripping it, before a coat of paint is applied. This requires the application of an acid that has a lower pH. You will need pH (litmus) test paper to tell you what the pH level is. Oxalic acid, phosphoric, and aluminum brighteners are commonly used as neutralizing agents.

For concrete, masonry, and used equipment, using A-400 Aluminum Brightener, followed by washing with R-109 to neutralize the A-400, and then finishing with a clear water rinse has been successfully used as paint prep.
Stain Removal

Stains are difficult, and no single product removes all stains. Three things affect stain removal:

*Source of the stain
*How long the stain has set
*The surface into which the stain has set

For stains on concrete or masonry surfaces, use an aluminum brightener, like A-400 or Delta 60™. Scale Away De-liming Acid Coil Cleaner is also a good stain remover.

For stains on painted surfaces, try DNB-1430 undiluted (caution: undiluted DNB-1430 can remove some paints) then A-400 or A-402 Aluminum Brightener.
Removing Carbon Deposits (smoke) from Engine Exhaust

Pre-spray with V-500 or DNB-1430 Liquid Concentrate cut 5 to 1. Wash with R-109, DNB-1430, or V-502. Alternately, pre-spray using A-400 Aluminum Brightener cut 20 to 1, and then wash using R-109 or DNB-1430.
Brushing also helps with heavy carbon deposits and smoke.
To Stop Spotting

Try the following procedures in the order given (the least expensive is first).

  1. Add W-200 Spray to your rinse. Refer to the section on W-200 Spray Wax for more information.
  2. Add RA-130 Liquid Concentrate to your rinse water, and cut 50 to 1.
  3. Add a water softener.
  4. Add a de-ionized (DI) or a reverse osmosis (RO) water rinse. Call Culligan to see which option is less expensive in your area. This always works, but costs have to be considered.

Cleaning Copper Trim
Almost any over-the-counter toilet bowl cleaner will clean and restore copper trim.

Spider Webs
Nothing will dissolve spider webs without dissolving paint and wood as well. D-limonene-based cleaners and ammonia work fairly well but may streak the paint, so it is best to test them before using them. Both 15- and Zero-degree nozzles (like the X-jet) work well for removing spider webs when using your pressure washer.  Grocery stores and janitorial supply stores sell “Spider Web Brooms” for removing spider webs. Fabric softener sheets will drive spiders away, so leave some scattered around, if possible.

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