The Rise Of Modern Polyurea Spray Coating Technology
For decades, coating and lining systems have been used for many applications. These initial systems, though complex in preparation at the time, were fairly simple to install. The common installation technique mainly involved brush/hand application.
Modern system developments and spray application evolution have enhanced coating and lining performance. New regulations and the move to higher solids content coating and lining systems required new means of application technique and equipment. This gave rise to the plural component application equipment. Due to the extremely fast reactivity and cure of the 100% solids polyurea elastomer technology, plural component equipment is required. This system must also be heated during processing, not for reactivity control but for the ability to atomize and spray correctly. High-pressure proportioners deliver the product to the impingement mix spray gun properly.
Proportioning Pump Basics:
To process these coating/lining systems, consideration must be given to the processing equipment. The key to processing is within the proportioning pump and the
spray gun. This is the “life support” system for proper installation and application. There are two types of proportioning pumps, vertical and opposed horizontal. These can either be air operated or hydraulically driven.
Proportioning Pump Types
Ideally, one would like to see comparable viscosities between each component. This aids in delivering equal volumes of material to the spray gun. Most systems
are processed at a 1:1 volume ratio. For proper proportioning and application of Polyurea spray elastomer systems, you must have the following:
• and Volume material flow.
Regardless of the type of proportioning pump used, these pumps must be able to heat the two components of the polyurea spray elastomer system. Heat is not required to promote the reaction of the system. That is built into the formulation. Heat is required to lower the mix viscosity of the two components as the reaction is initiated inside the mixing chamber of the spray gun. This initiation reaction causes a rapid viscosity build in the mixed system. The heat allows for proper atomization and spray ability of the polyurea system. This is much like high heating solids, conventional coating systems such that they properly atomize and spray. The heating output should be such that the delta T is a minimum of 70°F at full operation. Preheaters can be installed to aid in this for cooler climate conditions. It has been shown that the optimum spray pressure for the proper application of polyurea spray systems is at or above 2000 psi, coupled with a high flow rate and heat. Higher pressure allows for complete impingement mixing.
Material flow rate is essential if one uses vertical or horizontal instead of proportioning pumps. Many utilize a proportioning unit that will develop high pressure but lacks material output capacity to feed the spray gun properly. This is the same scenario when one uses a low-cost household pressure washer. You have “high” pressure but will not get the job done without volume water flow. This high pressure, low volume flow will result in the poor mix, atomization, and installation
of the material due to the fluid pressure drop at the spray gun.
The gun output
The proportioner capacity ratio must be less than 0.75 for proper operation and application. Careful consideration must also be given to the spray hoses. These must be heated hoses also. Depending on the overall length, the setup should include a “step-down” to
minimize pressure drop at the spray gun. The hoses may have an “accumulator” effect, so have a larger ID hose at the proportioning pump with a smaller ID section near the spray gun.
Hose Pressure Drop Chart
Remember that if you are in the bedliner business, the proportioning pump and spray the gun used may not be sufficient for high productivity field coating/lining applications.
Joint Sealant / Caulk Application:
While the main processing application of a polyurea system is spray applied, certain polyurea systems can also be dispensed using low pressure, low output units via a static tube mix procedure. These units are typically smaller than the spray units, although a conventional spray proportioning unit can be adapted for that use. This application finds a large market in joint sealant and caulk application areas.
Joint Sealant / Caulk Units
The units can either be a modified proportioning unit or a continuous delivery gear type pump. Since the polyurea systems are slower to react and have excellent flowability, high pressure and high output are not required. Remember that you only use this equipment to fill a small joint or saw cut on a horizontal surface.
Spray Gun Requirements:
Now that we have the pump basics described forgetting the conventional mix block and static mix application for polyurea spray elastomer systems. There are two types of impingement mix spray guns, those with a fixed
mixing chamber with a moving valving rod and those with a moving mix chamber/valving rod combination. Only the impingement mix types are appropriate for the fast cure, 100% solids aliphatic polyurea spray systems for the spray guns.
Impingement Mix Spray Guns
The basic concept for the mixing gun is that the material must enter, mix and then leave the mixing chamber of the spray gun as quickly as possible. Flow should not be restricted into the chamber concerning the overall volume of the mixing chamber of the spray gun.
A spray tip is often a must, even on the fixed mixing chamber, single valving rod spray guns to hold back pressure and finish off the mixing. No free flow of material.
Correct gun setup is crucial to a successful installation, as with conventional spray guns.
Something often overlooked with the spray guns is the filter screens used. Those used should be of the size that lets optimum material flow into the spray gun yet still filters any particles that would plug the chamber orifices.
Particle Size Conversions
US Mesh Inches mils Microns mm
30 0.0232 23.2 595 0.60
40 0.0165 16.5 420 0.42
60 0.0098 9.8 250 0.25
80 0.0070 7.0 177 0.177
Regardless of the spray gun is used, if you have a mixing chamber with 0.020-inch orifices, any gun filter screen used greater than a 40-mesh will only result in restricted
the flow of material into the mixing chamber and possible off-ratio application.
80-Mesh vs. 40-Mesh Screens
It must be noted that not all polyurea spray systems supplied are the same. Different processing conditions/spray gun setups may be required for optimum mix and performance. You might also require different spray gun configurations for different types of application areas. Refer your system supplier for the proper spray gun configuration for the system being used. And most importantly, a gun flush/service kit to properly clean and service the spray guns with all the functional accessories.
Material flow throughout the equipment setup must be matched. What does that mean? Well, you have a spray gun set up for 1.2 gallons per minute, and the proportioner can deliver up to 3 gallons per minute. Still, your material supply pumps (drum pumps) only put out
about 0.8 gallons per minute for low viscosity materials. With this setup, you are asking for trouble. This would lead to severe cavitation problems and off-ratio spray areas.
Many 1:1 drum pumps give good material flow rates at relatively low material viscosities. For the plural component systems, viscosities are much higher than typical paint systems. The 1:1 drum pumps just may not keep up during high output, large field applications. Therefore, 2:1 drum pumps are recommended. Ensure the material output for the product being applied as not all 2:1 pumps are the same.
Diaphragm pumps are also used quite successfully with plural component systems. For these pumps to work properly, a foot valve must be installed on the bottom of the dip tube. Otherwise, the material will drain from the pump and tube and lead to cavitation. Also, the supply hose diameter should be such that the higher viscosity material uses a larger hose ID. As much of the plural component application equipment technology has
derived from plural component rigid polyurethane foam systems, the material supply hoses concept has followed into the coatings area. For polyurethane foam systems, the resin blend component tends to have a higher viscosity than the isocyanate component; hence the hose for the resin was a larger ID. This is typically just the opposite for coating systems, especially polyurea systems. The material supply hoses should be at least the same ID, recommended at 0.750 inches (19 mm) each. This will ensure a good feed of material to the proportioning unit. An insufficient material supply package is a common oversight in equipment setup!
Generator / Air Compressor:
The generator and air compressor are essential for properly operating the application equipment. This is an area where many applicators and contractors fall short on. Before you set one up, you need to know the complete electrical requirements of your equipment
and the air pressure and flow rate needed to operate drum pumps properly, spray guns, and some proportioning units. All of this information is provided in equipment manuals. Sounds simple enough, but you would be surprised about what is used to cut corners
and costs. The air supply is only required for a hydraulic proportioning unit to operate the drum pumps and the spray gun. The airflow requirements may be slightly higher when using an air purge gun. For the air-operated proportioning units, a significantly higher airflow is needed. It should also be noted that air-operated proportioning units may be prone to freeze in cold, humid environments.
For the air compressor needs, the following is a general guide as published in the equipment manuals:
Equipment Air Flow at 100 psi
Drum pumps 2.0 cfm, each
Spray gun 2.0 – 4.0 cfm
Hydraulic proportioner 0 cfm
Pneumatic proportioner 50 cfm
Pneumatic drum mixer up to 75 cfm
To properly run a hydraulic proportioning unit, a minimum 10-hp air compressor, fitted with an 80-gallon tank, will be needed. For a pneumatic proportioning unit, a self-contained, commercial-grade diesel generator capable of continuously delivering 100 – 125psi at a minimum of 75 cfm will be required. From the generator perspective, there is also a considerable amount of discussion about whether you should have a single or 3-phase spray unit for the US market. The notion is
that the single-phase, 220-volt unit can simply plug into a normal power supply. The most common 220-volt service will not handle the required 75 – 100 amps
to power the unit properly. A 3-phase unit only requires a minimum of 50 amps for proper operation. A 3-phase setup also runs more efficiently.
In any event, a minimum of 25 – 45 kW generator will be required to properly power up the spray unit and any auxiliary equipment in most equipment setups. An air-driven proportioning unit does not exclude one from the noted electrical requirements. The primary heaters and hose heat do draw a considerable amount of current.
A very important aspect of the successful operation and application of the polyurea spray elastomer technology is your transportation trailer and truck layout. Now that you have the equipment, how will you lay it out? While everyone may have ideas about the individual layout, some important considerations exist. These notations will save you time and money by keeping everything organized and within easy access.
• Must have enough room for machine, material, and auxiliary equipment.
• Should have a good workbench with storage space/tool trays/surface deck.
• Workbench/area should include a vice for holding spray gun.
• Spray machine should be secured but not permanently attached.
• Load distribution should be such that no excess/overweight is placed on the tongue.
• Easy access doors (with the ramp) for loading drum sets of material.
• Hose storage rack.
• Good interior lighting with numerous approved electrical outlets.
• Good air compressor with supply / manifold system with air dryer.
• May also consider an air cooling system to reduce moisture build.
Various Trailer / Truck Views
The inside height clearance is one of the most overlooked aspects of setting up a trailer or truck. Why is this important? Well, what happens when you run out of a drum set and try to switch to another full set of material? If the inside height of the trailer is not enough, then you will not be able to insert the drum pump into the new material without trying to tilt the full drum. Good luck; these drums are full and weigh about 500 lbs (227
kgs). You will surely spill material and have a mess.
• Material drums are 34 inches (86 cm) tall
• Material drum pumps are 54 inches (138 cm) tall
• Inside height must be a minimum of 7.5 feet (2.3 meters)
“Moon Roof” Installation for Pump Removal
The organization is critical for production and performance in setting up your trailer/truck. A customer’s observation of how you might be organized goes a long way to the job you may do. Remember, visual appeal and how you are perceived in the industry carry a lot of weight!
The importance of proper safety equipment associated with applying plural component polyurea elastomer systems can’t be stressed more than enough. This includes respiratory protection and skin, eyes, and other people in the area. It may have been implied that only a dust mask was required in the early days. This is simply not enough!
The SSPC has recently issued Technology Update No. 8, “The Use of Isocyanate- ” Containing Paints as Industrial Maintenance Coatings,” which notes the use of “polyurea” systems. The report contains detailed information concerning the use of isocyanate types and the required respiratory protection. At a minimum, you will require an appropriate organic cartridge respirator fitted with HEPPA filters for dust particles. A prescribed cartridge change-out procedure will also be required. The isocyanates are not the only part of the system that requires safety. Since the resin blend component is a labeled corrosive material, appropriate skin protection is a must. Remember that you are also dealing with these materials under pressure; proper safety eye protection is also required. In addition to the information presented in that report and others, you must also follow the required rules as presented by OSHA and the local Department of Transportation. Transporting the materials also requires proper paperwork.
Safety in handling these materials and spray application is a major issue, and this paper is not designed to deal with all aspects. As an applicator, you are responsible for
Implement a safety program and directly communicate with your system supplier regarding the required safety equipment when working with their systems. It would help if you had an ample supply of related safety equipment:
• Extra masks: includes extra cartridge filters, STORE PROPERLY, use log;
• Fresh Air Supply: must be in a clean area, stored properly;
• Safety glasses/goggles: face shield for spray/splashback in hose depressurization;
• Hearing Protection;
• Communication Radios: between applicator and trailer person;
• Hard hats;
• Steel toe boots;
• Portable eye wash station;
• First Aid kit;
• Fire extinguisher;
• Blue nitrile gloves: approved for materials used;
• Tyvek suits;
• Drinking water;
• Industrial paper towels;
• Cat litter: makes good absorbent;
• Empty pails: for waste materials and gun flushing;
• Broom / Shovel;
• Trash bags;
• Iso Decontamination Solution for spill cleanup.
– water 90 – 95 parts
– aqueous ammonia solution 3 – 8 parts
– liquid detergent 2 – 5 parts
One of the keys to a successful installation is being prepared and ready for that installation. As difficult as it
may seem for some, YOU NEED TO BE ORGANIZED!
This organization starts with having the correct “tools” to do the job, including having your “tools” in a readily accessible fashion. The same holds for your spray application equipment. The following suggestions will help keep you organized and ready to spray promptly.
While your spray equipment purchase includes a small toolbox, this is not enough. It is suggested that this toolbox be used for the commonly used wrenches, pliers, drivers, etc.
You should also get a toolbox with sectional drawers and compartments to store all the backup spray gun parts. This includes the modules, Pattern Control Disks, gaskets, seals, and trigger rebuild kits. In this fashion, you can quickly assess your stock and order replacement parts before depleting your supply. If you have several types of guns, you should have a separate box. That way, you will not mix up the parts.
A full copy of the equipment manuals should be kept inside your trailer/truck cabinet. You can easily refer to the required parts or equipment troubleshooting. It is also recommended that you make copies of the pages out of the equipment manual that shows the exploded views of the pump and gun configuration, laminate, and post them above the workbench of the trailer for easy reference during disassembly and reassembly work. Also, have electrical schematics for proper troubleshooting in the field. In addition to the normal tools you may carry, these are some additional items that will come in handy out in the field:
• Gun flush kit: a must-have item for properly cleaning the gun;
• Spare parts:
• Bench vice: this is an important item and aids in the disassembly of the gun and
• Bung wrench: this is to open the bungs on the drums;
• 2″ bar stock: have a piece about 1 foot in length, 3/8″ thick. Use this with a
large pipe wrench to open those stuck or frozen bungs;
• Heat Gun: electrical heat gun to heat and help loosen stuck bungs;
• Vaseline: apply to threads on drum bungs to keep from sticking;
• Drum cart: makes moving drum a whole lot easier; pneumatic tires;
• Funnels: for transfer of material to avoid spills;
• Grease: white lithium grease or super-lube for lubrication of drum pumps,
air motors and trigger assemblies in the spray gun, drum bung threads;
• Duct tape: the wonder material has several roles;
• Volt Meter: for checking incoming volts, hose heat wattage (very important);
• Paper towels: might also have a box of cloth rags for cleanup work
• Misc: wood blocks (4″ X4″) for under drums edge, rope, staple gun, tie wire, electrical tape, hand cleaner.
Material Storage / Use:
A very important aspect of a successful coating application is proper material storage. The manufacturers and suppliers of the system do give recommendations for proper storage. These must be followed to ensure a good life in the system.
These basic procedures require that the materials be stored away from cold temperatures, extreme heat, and moisture. This means that the materials must be stored inside a building for protection.
The most sensitive part of the system is, of course, the isocyanate component. This material must be protected from freezing temperatures, moisture, and prolonged extreme heat. Isocyanate producers and suppliers note that the isocyanate will freeze when exposed to temperatures below 40°F (5°C) for extended periods. Technically, the material will begin to “polymerize” at temperatures below 70°F (21°C). When this happens, small crystals will form, and if left unattended, this will ruin the isocyanate component.
A general characteristic of using an isocyanate component that has been exposed to low temperatures for extended periods is that the resulting elastomer system may exhibit cracking when applied to “unsupported” substrates. This would include spraying over a geotextile membrane or bond-breaker type joint.
The isocyanate will also react with moisture, especially water. This will cause the product to solidify and this is not reversible. If moisture or water gets into the drum
and then seals, extreme pressures will be generated, and the drums may explode!
It is always a good practice to treat the resin blend component the same as that for the isocyanate component even though it is not sensitive like the isocyanate component. For the resin blend component, moisture will not “react in,” but it can contaminate the
component, which will lead to foaming in the elastomer system during processing. Some polyurea systems are less sensitive to these conditions than
polyurethane systems, but following good practices is a good idea. This will save you time and money.
General procedures for storage:
• Store material at 60°F to 110°F (16°C to 45°C). Do not store outside exposed to
• Store on pallets and not on bare concrete;
• Keep lids sealed and drums away from moisture;
• Keep away from extreme heat;
• Only open containers when ready to use; and,
• Use air desiccant or nitrogen blanket before sealing opened containers;
• Always agitate the resin blend before use as pigments do settle.
For drum mixers, use collapsible mixing blades such that the diameter of the mixing blades fully extended is one-third the diameter of the container or drum. This gives the optimum mechanical mix to the system.5
Collapsible Mixer Blades
Field Quality Control:
“Quality control in the field? I thought that the system supplier handled quality control of the preparation of the system; I just applied it.” That may be true, but the
systems manufacturers may have little to no control over how the applicators apply the system on every job. The coating system manufacturer/supplier uses the utmost quality control to prepare the blends for the coating system. As the applicator, you make the coating/lining product in the field. To have a top-notch, quality organization, a few quality and record-keeping issues should be used when applying coating systems. To protect your interests as the applicator, the application, and the integrity of the coating system, records
of the application and material used must be noted.
To do this, several steps must be followed:
1. Keep daily reports from the field/application;
• Weather conditions/dew point
• Substrate condition / preparation
• Coating systems used, including lot numbers
• Gel / tack-free time
• Spray equipment setup
• Problem areas
2. Spray a free film sample of the material used;
• This can be used in case there is a problem or issue at a later date
• Sample can be sent to test lab for confirming of system’s physical properties
• This sample is also a lasting record of the application
3. Check the film thickness of the system at various locations:
• Can use both non-destructive and destructive techniques
4. Check adhesion of coating system to the substrate:
• Use the Elcometer adhesion test. Having and implementing a Quality Control Program ensures application to application consistency and performance. This quality program can help secure that potential project/application when dealing with the end-use customer or engineering firm. For the program to work, you must use it. You must also have an equipment maintenance procedure in place. This will ensure a trouble-free operation of the application equipment from job to job. Many equipment/system suppliers have documented schedules available.
Now that we have had a look at most of the required individual components, what if we could roll it up into one complete package? This would mean having one unit that could power the application proportioner and be easily towed behind an average work vehicle.
The ability to turn one switch and have a generator, air compressor, and hydraulic application equipment all on and ready to go is not a dream.
Self-Contained / Skid Unit
A self-contained skid unit that utilizes one diesel motor to power the generator, air compressor pump, and drive the hydraulic pump all in an inline configuration is a reality. All are mounted “outside” the unit to allow for quietness and room to work. Using the hot water from the unit radiator will allow one to preheat the material and balance viscosities before entering the proportioning meter. Rather than trying to fight pressure loss and string out more than 300 feet of hose at the site, the skid unit can be easily moved or lifted by a crane within a few feet of the project. The small unit size allows for easy manipulation into very tight spaces. It also allows one to “down-size” the truck so that you don’t have to stop at every scale. The ability to go where no other complete rig can go!
Skid Unit on the Move
Over the past ten years, spray polyurea elastomer coatings have increased in importance as a method of lining and waterproofing applications in building and construction. Whether this coating will continue to grow in effectiveness and popularity or decline rests to a great degree on the job that applicators and contractors are doing now all over the country.
As you have seen, the spray polyurea elastomer technology requires the contractor to pay closer attention to detail than most other materials. Since the spraying of Polyurea involves the fabrication of a lining system on the job site, the process is subject to various environmental factors. The inability of the contractor or applicator to control environmental conditions, such as temperature, wind, and moisture conditions, be it rain
or humidity, requires constantly being alert to immediate and upcoming weather conditions. Due to the rapid gel times and cure of the technology, the processing equipment is very important.
It means storing materials at the job site by the manufacturer’s recommendations. It means checking to see that the materials are not too old and deteriorated. But, most important, it means knowing your spray equipment, how it works, and how to maintain it in good operating condition, especially when processing the polyurea technology.
Properly applying polyurea spray elastomer coating and lining systems does not just have the spray equipment that makes an applicator. It’s that plus all the accessory materials, training, organization, and record-keeping.