Polyurea is an organic polymer that is the reaction of isocyanate with an amine terminated polyether resin, forming a plastic-like or rubber-like compound that may be used in many of the same ways as older technologies - polyurethane, epoxy, vinyl ester, neoprene; to name a few.
Polyurea requires special training and equipment for field application, whether used as joint filler or as a field applied coating. VersaFlex has an ongoing program of contractor training in place. There are qualified applicators in all regions of the U.S. and an expanding network of qualified applicators throughout the world.
As a general rule, VersaFlex polyurea can be employed to contain any substance that may be directly discharged into normal sanitary sewer systems. It may be easier to give examples of environments where polyurea should not be used. As a general recommendation for constant exposure to direct chemical attack VersaFlex polyurea products may not be installed for attack by:
• Halogenated Solvents: 1. Carbon tetrachloride 2. Chloroform 3. Methylene chloride 4. Tetrachloroethane 5. Trichlorethene 6. Trichloroethane
• Non-Halogenated Solvents And Ketones: 1. Acetone 2. Acetonitrile 3. Acetophenone 4. Benzene 5. Butanol 6. Camphor oil 7. Cyclohexanone 8. Diethyl ether 9. Diisobutyl ketone 10. Ethyl acetate 11. Hexane 12. Methyl ethyl ketone 13. Methyl isobutyl ketone 14. Pentane 15. Phenol 16. Toluene 17. Xylene
• Acidic compounds with a total composite pH range equal to or below 4
• Basic compounds with a total composite pH range equal to or above 11 Note: Non-aqueous (anhydrous and anhydride compounds in granular, crystalline, or powder form) protected by an air drying system may be contained by polyurea. Consult VersaFlex.
• Amine Attacking And Amine Containing Compounds Strong, inorganic acids, organic acid halides, aldehydes, isocyanates, organic anhydrides. 1. Aminoethylethanolamine 2. Aniline 3. Ethylamine 4. Methylamine 5. Pyridine 6. Toluenediamine
VersaFlex polyureas begin to develop their physical properties within minutes of application. Among several very desirable properties are their quick gel time and their glass transition temperatures that average -40 degrees F and +480 degrees F. Heat of deflection under no load is +250 degrees F. Safe upper limit of working temperature is +350 degrees F, under no load. Polyurea will exhibit thermal shock debonding when subject to repeated periodic blasts of live steam. While polyurea has high glass transition and heat of deflection temperatures, it will burn when exposed to direct flame. It will self extinguish when flame is removed.
Polyurea may be either hard or soft depending on the particular formulation and the intended use. Durometer ratings may range from Shore A 30 to Shore D 80.
VersaFlex has run abrasion resistance testing according to ASTM D 4060 using the most aggressive abrader, the H-18 wheel. The abrasion loss is as noted in our material specification data sheets for the appropriate material. This test was utilized because it most nearly typifies the type of abrasion attack found in industrial environments.
The industry standard testing for polyurethanes uses the abraser CS-17 wheel. This wheel is a much smoother, less abrading mechanism than the abovementioned H-18 abrader wheel. The most severe utilitization of polyurethanes is found on parking deck coating systems.
The hard polyurethane topcoats used in these systems generally have CS-17 losses between 5 - 10 milligrams. FSS 45DC and FSS 50DM report H-18 loss between 180 and 250 milligrams. This loss is actually much less severe than a loss of 5 – 10 milligrams on the CS-17 wheel.
VersaFlex polyurea may be applied to properly prepared A-36 metal substrates. The metal should be blasted to Near White or White, and have a blast profile of 5 mils. Adhesion values will exceed 1000 psi without using primer.
There is no hard and fast number that is useful to the designer. Generally, an adhesion value is a compromise between the type and condition of concrete substrate, the stresses placed upon the membrane prior to project completion, and the requirements of the membrane to withstand in-place use stresses. Where possible, concrete should have all surface paste removed and be free of laitance of any kind. A texture similar to 80-grit sandpaper as a minimum is desirable.
Since concrete has low tensile properties, especially at the surface faces of large plan areas, one rule of thumb is to expect adhesion to range around ten percent (10%) of ultimate compressive strength of the concrete. The best that can be expected is in the range of 350 psi to 450 psi for 4,000 psi concrete properly cured and of sufficient age to acquire its maximum physical properties.
Polyurea products from VersaFlex are based on diphenylmethane diisocyanate (MDI) or 1,6 hexamethylene diisocyanate (HDI) polymer technology. These polymers have a low vapor pressure which corresponds to a low evaporation rate.
During the mixing, installation and curing process of all polyurea, the release of any free monomers is virtually non-existent. The chemical design of these products entails an extremely rapid reaction between the molecules in each component. This rapid reaction coupled with the lack of any evaporative characteristics allows these products to fall well within safety guidelines established under OSHA and ACGIH. The installation of these products may be made in incidental food contact locations and are certified under the FSIS procedures of the USDA.
Self-leveling polyurea products have been tested under field conditions during application for CalTrans (California Department of Transportation), with the detection of no free molecules in the environment. Review of MSDS information is recommended prior to handling of any products. When polyurea products are spray applied, use of an OSHA/NIOSH approved respirator should be a standard required procedure.
Prior to overcoating polyurea make sure it is clean. For the first several hours after polyurea has gelled it may be suitable for overcoating without further preparation. If polyurea base coat material has been in place for longer than six hours there could be problems with inter-coat adhesion.
Since fewer products are carried in aromatic solvent, which tacktify polyurea you must undertake this process. To assure inter-coat bond apply a liberal amount of denatured alcohol (or more aggressive solvent such as acetone or MEK) to polyurea and allowed to evaporate completely. This will re-tack the polyurea base coat and allow proper adhesion of the follow-on overcoat.
This same procedure should be used when bonding polyurea to polyurea after initial cure has taken place.
Actually there are two different types of aliphatic polyurea systems currently on the market. One is the typical high pressure/temperature sprayed systems and the other is what is known as a "polyaspartic polyurea" type system. This polyaspartic system is different in that it uses an ester based resin component and has a longer pot life. It can be hand applied using close nap rollers; brushes; rakes or even airless sprayers.
The aspartic systems are not the high build coating typical of the "hot spray" polyurea systems. The typical aromatic polyurea systems must be processed through high pressure, heated plural component pumps and sprayed through an impingement type spray-gun. This is true also for the aliphatic version of this type of system, the primary difference being the color stability of the aliphatic systems.
The following ASTM standards can be a useful guide when you prepare concrete surfaces.
For more information on these or other ASTM standards, visit www.astm.org.