Guide for Selecting Roof Coating Spray Equipment
Spray Equipment Overview
While roof and wall coatings can be applied via roller, brush, squeegee or spray, the most cost efficient way (especially for large jobs) is the airless spray. Using this method, the coating is pumped from the container to a pump where it is pressurized to several thousand pounds per square inch (psi). The coating is then sprayed through a gun with a small orifice, or tip (usually 0.025- 0.040 inches). The coating comes out of the tip at very high pressure and when it is exposed to the atmospheric pressure it disperses into discreet droplets.
Typically airless spray units are characterized by their spray rate, listed as gallons per minute (gpm), and their pressure. The number of spray guns that can be operated from the same unit are often listed also. Larger units will allow for longer hose runs. This can be helpful on large roof jobs where the coating and the airless spray unit can be kept on the ground and only the hose and gun are actually on the roof.
When deciding if an airless spray unit should be powered by either an electric motor or gasoline engine, consider the following: A gasoline airless sprayer is fully self contained. In contrast, an electric motor, although less prone to the complexities associated with a gasoline engine, may require a very long extension cord. There is an appreciable electrical current drop when using a long extension cord, and this can adversely affect the motor’s efficiency.
If the airless spray unit has a filter, this should be removed. While the filter is needed for applying fine finishes and enamels, it merely increases the “back pressure” on the unit and lowers coating throughput.
There have been recent innovations in airless sprayers for home painting use, making them more affordable for the “do-it-yourselfer”. However, these typically have low volume and pressure, making them inefficient for applying coatings.
Spraying Acrylic Coatings
Using the airless spray method, pressurized acrylic coating comes out of the gun at atmospheric pressure. The pressure reduction then causes the coating to atomize into small discrete droplets. The main benefit of using this method is that any entrapped air is released.
For successful acrylic coating application, the equipment should have a delivery rate of 1.5 gpm, and the pressure should be at least 3,000 psi. A “Reverse-A-Clean” tip with a minimum tip size of 0.033 inches is recommended. However, The tip size can be increased to 0.045 inches for greater throughput. Note: Always size the tip to the pump output.
Spraying Asphalt Emulsion Coatings
Much larger volume equipment is recommended for the application of asphalt emulsion coatings. These emulsions are typically applied, with or without scrim or strand reinforcement, at a much higher rate than acrylic coatings. Sometimes as high as 5 gallons per Square (100 ft2), per coat. In this case, the asphalt emulsion acts as the primary waterproofing, and this high film thickness can build slope and fill in alligator cracks and cover gravel ballast.
Because of the high throughput volume required for the application of the asphalt emulsion; the emulsion isn’t sprayed, but rather fluid applied. While the acrylic coating airless spray is fully atomized into discrete droplets, the asphalt emulsion streams out in a flat, fan shaped array. To achieve this, the largest tip size should be used, sometimes as large as 3/16 inches.
For successful asphalt emulsion application, the equipment should have a delivery rate of at least 3-4 gpm, and up to 15 gpm. Pressure should be at least 1,000 psi. The tip size should be at least 0.035 inches. Note: Always size the tip to the pump output.
Spray Equipment Recommendations
Intech Equipment & Supply, a leading spray equipment distributor for commercial roofing, offers a number of customized Graco spray packages that have proven to be very reliable for the spray application of acrylic coatings and asphalt emulsions. Below are a few recommendations:
For applying acrylic coatings, the GH833 has a maximum output of 4000 psi at 4.0 gpm, and maximum tip size of .065. The GH300 is a lower profile spray package that has a maximum output of 3300 psi at 3.0 gpm, and maximum tip size of .055.
For asphalt emulsions the GH1017 has a maximum output of 1000 psi at 16.5 gpm, and the GH2570 supplies material at 2500 psi at 7.0 gpm. Larger diameter fluid hoses are typically used to minimize the pressure drop in the fluid hoses out to the spray tip.
An excellent “all around” sprayer that can apply both acrylic coatings and asphalt emulsions is based on the GH733, and supplies coating at 3500 psi and 3.0 gpm, and maximum tip size of .055. Adding a 1017 pump lower is commonly used for emulsions and has a maximum output of 1000 psi at 16.5 gpm. Larger diameter fluid hoses are used, and we recommend that they be dedicated for emulsions only. Coatings and Emulsions will each have dedicated fluid sections including a pump lower, hoses and spray gun or dispense valve. The GH733 has 5 different pump lowers that allow you to match the best pump output pressure and flow rates for each material. Intech Equipment & Supply, with 6 full service branches in the U.S., can customize your spray equipment by properly sizing fluid hoses and lengths, and adding productivity enhancing accessories to match your material and application requirements.