The key to a quality, long-lasting SPF roof system is proper preparation and application.

Since the introduction of spray polyurethane foam in the ‘60’s, more roofing contractors are offering this versatile roofing system to their clients as an alternative to conventional roofing systems. SPF is a two-component fluid material that rises into a closed-cell mass when ratioed, mixed and sprayed. Once cured, SPF is weather resistant, seamless and provides superior insulating qualities. Furthermore, the material can be applied over most surfaces and is easy to maintain.

The key to a quality, long-lasting SPF roof system is proper preparation and application. The roof surface must be clean and dry for proper adhesion. Environmental conditions such as surface moisture, high humidity, wind and low temperatures may lead to a poor roofing job. The correct application equipment is also important to producing a quality sprayed roof. A state-of-the-art SPF unit is easy to use, easy to service, ensures optimum performance from the SPF material, reduces waste and increases production.

A typical SPF application unit or proportioner includes supply pumps, console/electronics, proportioning system, primary heaters, a heated hose and spray gun. Some systems provide data reporting so a contractor can verify that the plural component coating or foam system was applied correctly. A contractor can supply the building owner with this data showing that the job met the roof system specifications.

It's important to remember that optimum temperatures and pressures must be maintained to obtain proper chemical mixing.

System Operation

Low-pressure feed pumps transfer the isocyanate (part A) and resin (part B) from drums to the proportioner. The proportioner must be able to accurately proportion the two components within plus or minus 5 percent by volume. It must also offer enough pressure and heat to adequately pump the isocyanate and resin to the target application area where the materials will be mixed in the spray gun. The viscosity range of most isocyantes is about 250 cps to 350 cps at 70 degrees F while the resins range in from 400 cps to 3,000 cps at 70 degrees F. In addition, the proportioner’s electronics should offer easy problem identification and problem troubleshooting. A state-of-the-art proportioner will provide diagnostics, data reporting, pressure readout, temperature and pressure controls, as well as automatic shutdown capabilities to ensure that the system performs to the material supplier’s specific requirements.

From the proportioner, precise ratios of isocyanate and resin are pumped through a moisture-resistant, heated hose to the spray gun. The hose is usually available in 50-foot lengths. Most roofing contractors prefer hose sections up to 300 feet long. This is long enough to reach multi-story roofs and cover most roof surfaces, while maintaining the correct pressure.

The hoses are designed to maintain temperature to the material’s specs. Typically, application temperatures range from 0 degrees F to 110 degrees F. Proper temperature control of the material to spec should only take a few minutes and the proportioning system should maintain this temperature the entire day.

The last system component and the most important part of the system is the spray gun, according to many contractors. The gun should allow for pattern and output changes and produce a uniform spray pattern. This uniform spray pattern is key to proper product distribution to the target. Although the optimum fluid pressure to spray most foam materials is normally between 800 psi and 1,500 psi, many other plural component systems require maximum fluid pressure up to 2,000 psi.

It’s important to remember that optimum temperatures and pressures must be maintained to obtain proper chemical mixing. Maintaining tight control on these settings produces a rigid polyurethane foam that offers the physical properties represented on the material supplier’s data sheet.

Immediately upon mixing, the two components react chemically and start to expand to approximately 30 times the original volume. As the foam rises, it bonds to the roof surface and sets into a solid, seamless insulation within 3 to 20 seconds.

Applying SPF

Before spraying SPF, remove and repair all blisters, loose flashing and other defects. Thoroughly brush and vacuum the roof, removing loose gravel, dirt and moisture. Observe all safety regulations when working with SPF and wear the proper safety clothing and equipment.

The applicator’s first job is to spray around all pipe sleeves, boxes, ducts, etc. This assures water will not leak around these objects. It also provides extra foam buildup so that water does not pool around them.

Since the hoses are relatively heavy and bulky, it is advisable to have a hose man to work with the applicator. It’s his job to keep the heavy hose out of the way of the applicator. He also supplies a second set of eyes to inspect the job as it is progressing and he can alert the applicator to obstructions in his path or safety concerns.

For mobility, the applicator usually cradles the hose on his shoulder and, keeping the gun perpendicular to the roof surface, works backward, overlapping the pattern by 50 percent. A normal spray pattern is 3 feet to 4 feet wide. The applicator normally sprays the foam between 1/2 inch to 1 1/2 inches thick per coat, building up the thickness to the specified amount.

As the operator triggers the spray gun, the material is mixed in the spray gun’s mix manifold and expelled through the air cap and spray tip. The optimum spray pattern is a perfect circle that is round with a uniform thickness. Pressure and heat controls allow the operator to fine-tune the pattern for optimum performance.

If the temperature of the SPF is too cold, the pattern will tend to spatter and splash the roof surface, resulting in an uneven pattern. If the SPF is too hot, a split pattern will appear. If the pattern is distorted, there may be too much air on the air cap or there is a buildup of foam on the air cap or spray tip.

Keeping a clean gun is important to achieving an optimum spray pattern. New spray guns are designed with special air caps that reduce buildup and tip clogging, as well as check valves and screens that are easy to maintain.

After the SPF has been applied, the cured foam must be covered with an elastomeric coating or aggregate covering to protect the foam from ultraviolet rays and premature surface degradation. Foam begins to weather within 72 hours, so it’s important to get this protective coating or covering down quickly for optimum adhesion of the coatings. Airless sprayers are usually used to apply the elastomeric coating.


New application systems have been designed for easy cleanup and maintenance. The only part of the whole system that contains mixed foam is at the spray gun’s head. In one example, the need for removing this material has been reduced significantly with Graco’s introduction of the Quick Shot grease port. At the end of the day, the applicator simply shoots grease into a port on the head of the gun. The grease forces the mixed material from the air cap and tip, coating the entire fluid section to prevent moisture exposure. It takes only a couple of seconds and ensures that the gun is ready to spray the next day. This feature, as well as many others available on the market, is designed to increase production and reduce waste.

According to several raw material suppliers, system compounders and applicators, the SPF industry has been growing for the last several years. Some estimates range in the double-digit area. Couple state-of-the-art application systems with improved SPF materials, reliable information and better trained, crews, and you’ll be applying a roofing system that will provide decades of protection with little or no maintenance.