Pollution Prevention Tips for Spray Painters
A Publication of the Georgia Pollution Prevention Assistance Division
Many companies across Georgia apply paint using spray guns. Some companies apply paint as their main business, such as automobile repainters. Others apply paint as a sideline or for maintenance of their buildings. Here are some steps that can reduce waste and save money.
A typical painter will use a high pressure spray gun to apply coatings. High pressure guns are powered by compressed air. The purpose of the gun is to turn the liquid paint into a mist (atomize) and propel the paint toward the surface to be painted. When the wet mist contacts the surface, some of it sticks and some of it bounces off of the surface. Under ideal conditions, only about 30% of the paint sprayed sticks or is transferred to the surface using a high pressure spray gun. This is termed transfer efficiency; high pressure spray guns have a maximum transfer efficiency of 30%. This means that if a gallon of paint can coat 300 square feet, it will only coat 90 square feet if applied with a high pressure spray gun. In real life, the transfer efficiency is often as low as 15%; that gallon of paint will now only coat 45 square feet. This becomes important if the cost of the paint is considered, as one gallon can cost $20.00.
There are several common causes of low transfer efficiency. High pressure spray guns operate best at about 50 pounds per square inch (psi) air pressure; the correct pressure varies depending upon the gun manufacturer. Spray systems are often incorrectly operated at 100 psi; this results in more bounce back of the paint and much more waste.
Another cause of low transfer efficiency is use of poor painting practices. Painting requires skill and knowledge. Many painters have never been trained in painting methods that will reduce waste and improve quality. Holding the paint gun too close to a surface will result in increased bounce back and poor quality due to runs. Holding the gun too far away will result in paint drying before it reaches the surface and reduced coverage. Maintaining the correct distance between the gun and work surface, moving the gun at the correct speed, maintaining an overlap of 50% between strokes, and moving the gun perpendicular to the surface (not in an arc) will result in higher transfer efficiency and better quality. Correct painting methods and correct gun pressure settings can increase transfer efficiency from 15% to near 30%.
The cost savings can be substantial. For example, painting 3,000 square feet of surface with a transfer efficiency of 30% will require 33 gallons of paint costing $666.00 at $20 per gallon. Painting the same 3,000 square feet using poor methods (15% transfer efficiency) will require 66 gallons costing $1,333. Paint and equipment vendors, technical schools, and trade organizations are all good sources for obtaining training for painters.
Another method of increasing transfer efficiency is to use a High Volume, Low Pressure (HVLP) spray gun. These guns are capable of a transfer efficiency of about 65%; some are capable of 90% in specialized situations. If an HVLP gun with a transfer efficiency of 65% was used in the above example of coating 3,000 square feet, only 15 gallons of paint costing $300 would be needed. Using an HVLP gun would save at least $366 in paint cost. HVLP guns are available from many sources including popular catalog suppliers. A basic HVLP gun will cost about $350; an HVLP gun would have paid for itself in the above example. If a company completed ten jobs annually, the savings would be $3,600.
Transfer efficiency is only part of the equation. Cleanup of paint equipment between jobs is another major consideration. Painting should be scheduled so that color changes are reduced. Color changes often result in washing paint guns and lines; this generates air emissions of cleaning solvents and results in the loss of any paint still in the paint cup or lines. Even when color changes are required, changing from a light color to a dark color often requires less cleaning.
Another way of reducing air emissions is to switch to water-based or high solids paints. Both types use a reduced amount of solvent. A typical solvent-based paint may contain 6 pounds of solvent per gallon of paint; high solids or water-based paints may contain less than 3 pounds of solvent per gallon. Water-based paints will have about the same coverage as conventional solvent-based paints; high solids paints can have twice the coverage per gallon, about 600 square feet. This is important to know when comparing costs. Drying time and performance, in addition to coverage, of high solids and water-based paints can be different from conventional paints.
Pollution Prevention Check List for Spray Painters
The Pollution Prevention Assistance Division (P2AD) is available to help Georgia companies reduce waste and increase profits through pollution prevention. Services range from telephone assistance to on-site evaluations and consultations. The service is free, confidential, and non-regulatory. For more information call Jancie Hatcher at 404.651.5120, 800.685.2443 in Georgia, or e-mail at firstname.lastname@example.org.