Roof Coatings Articles

Building a Commercial Roofing Rig

Photo courtesy of CJ Spray, Inc.

Editor’s Note: To find out more about how to choose the proportioner, check out this article from the 2016 Roof Coatings Supplement of CoatingsPro here.

Choosing the necessary spray equipment for a roof coating project, especially one that includes spray polyurethane foam (SPF), can make a big difference. In addition to choosing the right proportioner, you must also choose a generator, air compressor system, and container.

Generating Power

If the kitchen is the heart of your home, a generator is the heart of any mobile spray rig. SPF proportioners have become very advanced over the last few decades. This technology requires consistent and reliable power to keep the electronics running correctly and safely. Under-sized generators create spikes in voltage and frequency fluctuations.

Look at the total power requirement of all equipment in your mobile rig, which may consist of the sprayer, air compressor, air drying equipment, heaters, air conditioners, lights, and other tools. Once you have your total amp draw, add 25 percent as a buffer. Most roof rigs use a 40–45 kw diesel-driven 240-volt, 3Phase generator. For budgeting purposes, also consider you will have additional costs and components for installing such items as a main on/off disconnect, breaker panel, wiring, and conduit. You will also need to properly exhaust the diesel fumes outside your rig. Building a dividing wall separating the generator and spray/work room should also be done to further protect workers from exhaust and noise.

Air Compressor System

An SPF spray system has multiple air-operated pieces of equipment that will require an air compressor. As you did with a generator, you will need to add up the total air requirement of the equipment you are using and add a buffer. Feed pumps go into both the A and B component drums to push the material to the proportioner. Each will require between 4 and 7 CFM (0.1‒0.2 m³/min.) depending on the pumps you choose. Spray guns take approximately 4 CFM (0.1 m³/min.), but that air requirement is when the feed pumps aren’t running so you do not have to add that to the feed pumps’ air consummation for you total air usage.

You may also choose to have a high-pressure breathing system, which is especially important when spraying in any kind of confined environment. There are other air-operated accessories, such as foam scarfer equipment that shave off excess foam, and have large air requirements. Most contractors use an electric air compressor that will take power from the generator, so be sure to use that in your calculation.

Electric reciprocating (piston driven) compressors take a large in-rush of current when they first turn on, so when buying a reciprocating compressor make sure you add a constant run valve. This means it does not stall and turn off when it reaches pressure. The compressor will bleed the pressure off and the motor will continue to run, providing a constant power draw from the generator. This means the compressor is running all day while you spray, so buying a high quality reciprocating compressor is important for longevity.

With compressors, you get what you pay for. Commonly, contractors will purchase a 5–7.5 hp reciprocating compressor, which provides 17–23 CFM (0.5‒0.6 m³/min.). If more air is required for running your breathing systems, tools, or a pneumatic proportioner, you may want to look into a screw or rotary vane style compressor. There are also manufacturers that build combination generator and compressor units that are specifically designed for the SPF industry.

It is also important to remove the moisture created from the air compressor. Most spray guns used in the SPF roofing industry are air purged, meaning the residue of A and B is blown out of the mix chamber with air supplied from the compressor. Any moisture in the air will increase gun maintenance. Clean, dry air will also improve the longevity of the feed pumps and agitator (if required). A well planned mobile rig will have a high quality moisture trap and electric refrigerated dryer. The moisture trap is installed inline after the compressor and removes water particulates. The air then passes into the electric dryer, which is 110 volt and will provide reliable dry air by lowering the dew point.

When sizing an electric dryer, make sure it is rated for both the CFM of the air compressor and the inlet temperature of the air. Air exiting the air compressor is hot and varies by the type and size of the compressor. For example, a screw compressor will have hotter air than a reciprocating compressor requiring a higher performing dryer. You should be able to collect the air outlet temperature from the air compressor manufacturer’s specification sheet.

Finally, you must have a way to regulate the air pressure going to the different pieces of pneumatic equipment. Most rigs will have three air regulators: one for each feed pump, typically regulated between 65 and 85 psi (448.2‒586.1 kPa) and one for the spray gun, 100 psi (689.5 kPa).

Containing the Rig

Only you can decide if a truck or trailer fits your needs better, but keep in mind space and gross vehicle weight. Add together the weights of each piece of equipment and then decide how many sets (i.e., the number of drums for A and B sides each) you will need to carry. Trailers also have the added complexity of balancing the load so it tows well.

You need to ensure that it hauls well on the way to the jobsite when you are full of material and on the way home when the drums of material are empty. This is not an easy task, and all too often you see trailers that are tongue heavy where the truck looks like the rear tires are going to blow, or they have such little tongue weight you can’t drive over 40 mph (64 km/hr.). Regardless of what you choose, you should consider the following:

Maintaining Temperature: During storage, material should stay warm and never get below 37° F (2.8° C). During application, the materials in the drum should be between 65 and 85° F (18.3‒29.4° C). If the material is cooler than 65° F (18.3° C), the proportioner will have a difficult time getting it up to spray temperature. If the material gets too hot, you risk the blowing agent (the component that gives foam its expansion) outgassing prematurely, reducing your yield (board feet per lb.), and costing you money. Make sure to well-insulate your container (using spray foam of course), and use heaters and/or air conditioners to maintain temperatures.

Interior Ceiling Height: As you go through material at the jobsite, you will need to swap feed pumps from empty drums to full drums. Depending on the pumps you choose, you will need 6.5‒7' (1.9‒2.1 m) of interior height in your trailer or truck to get the pumps to clear out of the drums. An interior height of 7.5' (2.3 m) is recommended in your rig to easily change out drums.

Prevent Isocyanate Crystallization: Isocyanate is very moisture-sensitive and will begin to harden into crystals with even slight exposure to humidity. Crystalized isocyanate is very difficult to clean and typically results in expensive repair bills. The longer the SPF equipment sits idle between jobs the higher the risk of crystallization. There are some simple tricks to help alleviate the problem. Use a desiccant cartridge when venting the A side drum. It threads into the ¾" (1.9 cm) vent cap on the 55-gallon (208.2 L) drum lid and removes the humidity from the air as the liquid in the drum is replaced by air. Also, use a moisture-resistant supply hose between the isocyanate drum’s feed pump and the proportioner. Even a moisture-resistant hose allows humidity to penetrate over a two-week span and starts affecting the crystallization process. A hydraulic hose, with little moisture resistance, takes half that time. Humidity will also penetrate the heated spray hose, which at $2,000 per 50 feet (15.2 m) is an expensive and preventable repair. Installing a heated hose circulation kit allows you to easily circulate the material from the drums, through the proportioner, down your heated hose, and back into the drums. Do this every two weeks and you should be fine for the shelf life of the material.

Prevent Worker Exposure to Isocyanate: Try to prevent spills and respiratory exposure by sealing drums with the feed pumps’ threaded mounts. Also use construction materials that allow you time to clean up a liquid spill before it soaks into a substrate, such as a floor coating or metal workbench.

Worker Respiratory Protection: When working in any kind of confined space, such as inside commercial or residential buildings, use a positive pressure supplied-air system. These include high-pressure breathing systems that work off your system’s air compressor, portable electric ambient air pumps, or a powered air purifying respirator (PAPR). Do your homework and select what works best for your situation. Ventilating a confined work space is equally important and selecting the right exhaust fans and blowers to remove contaminated air and bring in fresh air is vital.

Tailor Made

Building the right rig for your company’s needs take time and forethought. Of course, certain aspects can be altered if you need more hose down the road, for example, but taking the time to plan ahead now can help save you money and energy in the long run.

About the Author

Chris Bryntesen is president and CEO of CJ Spray, Inc., one of the leading manufacturers and integrators of turn-key spray foam rigs. For more information, contact: CJ Spray,

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