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Frequently Asked Questions
It is not a good idea to utilize a polyurea system in constant exposure to gasoline. The solvent level in gasoline will cause the polyurea to soften and swell as you have indicated. The softening could very well progress to the point of failure and certainly the systems other physical properties would be significantly compromised. There may be some systems available that can tolerate constant gasoline exposure. You should call a few of the PDA member manufacturers to get some references.
At least 70% of all coating / lining application failures over concrete are due to poor or improper surface preparation. This is a true statement that is discussed in many of the NACE, SSPC and ICRI courses on concrete coatings work. There are some very valuable pieces of information that you have omitted from your description of this application, namely size of the area and time to do the application. You have already noted that there are some pits, but in what condition is the remainder of the concrete? Your prep work may involve the use of degreasers or other cleaners to remove contaminants. An abrasive blasting procedure may also be required to remove laitance that would lead to delamination of the applied coating system. As you can see, there is no simple, fast cure answer. With regard to your question on a fast cure material for filling the pits, agrigate filled epoxy systems have been used quite successfully for this purpose. Many of these are low viscosity systems in the neat form that penetrate into the substrate. The agrigate would then be used in the "filler coarse" of the system. Typically, polyurea spray system can be applied over these within a matter of hours. Another very viable method would be to use a slow cure polyurea joint sealant type system to fill the pit areas. This procedure has also been used quite successfully and is being used today. Agrigate can be introduced, depending on the depth of the pit. The whole surface area would need to be prepped and then primed with a good penetrating primer system. The pit areas could then be filled, allowed to cure and then coat with the polyurea system. I would suggest that you keep all traffic, or as much as possible, off the prepared substrate before completing the project. Small "spot repair prep work" may be required before final application of the polyurea system. Another material would be the fast set cementicious materials. Caution must be used here as thin films of these do not "cure" properly and leave a very friable / dusty substrate. This would lead to disbonding of the coating system. The best advice would be to refer to the polyurea system supplier for guidance on compatible
A polyurea system which may have the ANSI/NSF-61 has complied with certain criteria required by that testing protocol, however, it is important to review the proposed installation configuration to know whether the "approved system" has met the particular aspects of the ANSI/NSF-61 protocol which is relevant to that proposed use. There may be subdivisions of use within an "approved" category and unless a system meets the requirements for a particular subdivision it may still be inappropriate for that particular use. It is recommended that contact with the supplier of the system be made and full analysis of the intended use covered with that company. The ANSI/NSF-61 testing does not cover physical properties of the system such as elongation, tensil or chemical resistance. There may be a general relationship between the qualities in a system necessary for becoming approved and those physical properties, but again the proper procedure would be to contact the vendor about their particular system and the proposed use. As per UL's ANSI/NSF-61 approval, the published companies on their web site and product is as follows: Semstone 403 from Plasite EnviroLastic AR 520PW from General Polymers.
There are several ANSI/NSF-61 qualified pure polyurea systems available from member manufacturers. The rather wide joint will need to be filled with a high quality two-component urethane caulk or grouted with a semi-rigid epoxy filler before the coating over everything with the polyurea system, but otherwise this is a pretty typical application for polyurea systems.
First off, "polyurea" is a generic term used to describe a type of technology. This is the same as "epoxy" and "polyurethane" for other types of technologies. As there are numerous formulation possibilities for polyurea systems, which include spray, joint sealants, aromatic and aliphatic based, it is not possible to get "polyurea" approved through UL or any other certification system. It would be appropriate to achieve certain approvals on specific formulations / product trade names. In this case, I assume that you are referring to UL approval from the standpoint of fire rating. At this point, we are not aware of any polyurea system where the sole material has the UL approval. There is a "coating system" that does have approval. This is comprised of an aromatic polyurea base coat with a top coat of a moisture cured polyurethane system. This is being supplied by one of the PDA Member companies. In addition, there are two aromatic based polyurea systems that have the UL ANSI/NSF-61 potable water approval. This does not mean that "polyurea" is approved, but these 2 specific systems / formulations are. It would be possible to receive the UL rating for insurance purposes that you are referring to. It would be up to the individual "polyurea" system supplier to submit for this testing and then follow the guidelines for application / installation. Unfortunately, the Polyurea Development Association is not in a position to submit and receive such approvals.
The polyurea technology in general has good resistance to low concentrations of sulfuric acid at normal operating temperatures. In concentration of less than 10%, at relative ambient conditions, polyurea systems perform well. If that concentration is exceeded, or if the exposure temperature is increased, breakdown of the polymer can and will occur. The same holds true for hydrocarbon exposure. Certain low molecular weight hydrocarbons may tend to penetrate the polymer and are absorbed causing swelling and softening. This is a characteristic of the polymer backbone of the various formulations. Much of the chemical resistance of the polyurea technology is significantly dependant on the specific polyurea formulations used. There are some that have better acid resistance than others while certain formulations offer better hydrocarbon resistance.
There are many versions of the "polyurea" technology as with "polyurethane" technology. While the PDA is mainly focused on the plural component type materials that are "field" applied at this time, your question opens the door to an new age of the technology. The term "polyurea" is a descriptive one that identifies the type of organic linkages found in the polymer backbone. There are numerous possibilities of how that linkage is formed, or put together if you will. There are numerous references to a variety of "polyurea" polymers that are also used in medical applications. The "polyurea" technology in general is very resistant to water and common printing inks, though the printing inks may stain the polyurea depending on the complete polymer backbone. The "polyurea" you have come across in the patent search is produced in an aqueous type media such that spheres / balloons of the polyurea polymer encapsulate the ink material. This can then be deposited to various substrates such as that found in carbonless carbon copy paper. When pressure is applied in localized areas, the spheres burst and release the ink to make a "mark". This that is described is oversimplified of course of the actual procedure. "Polyurea's" can be deposited by vacuum though we don't feel that any of the current members of the PDA have any experience in this area. Most of the application techniques we see are those where the "polyurea" system is applied via plural component technique. The 2-components that form the polyurea polymer are mixed in either a high pressure, high temperature impingement mix spray gun and applied to surfaces at film thickness of 0.38 mm or greater or by using a low pressure pour / static mix technique for joint sealant applications. For the application you speak of, the "polyurea" would need to be formed in a solution / suspension and deposited on the substrate. That solution / carrier media would then dry / evaporate and the polyurea polymer film formed. As far as the MSDS is concerned, there are many specific MSDS's relating to individual companies 2-components of the polyurea system. We are not aware of any MSDS on "polyurea".
Its the period of time during which another coat of product may be applied to previous coats of product and still obtain good adhesion/results......a window of time. Different products have different periods during which acceptance of additional coats will be optimized.
Polyurea membrane systems are indeed excellent waterproofing materials. They can be applied over wood surfaces using the proper steps. Typically wood, especially plywood or OSB, has significant moisture content and general porosity that make the use of systems producing heat upon cure problematic. Usually to successfully coat a wood surface with the typical sprayed polyurea system it is necessary to apply a good primer that will effectively seal the surface against moisture/vapor emission. There are a several polyurea based systems that might be considered for this type of application depending on the objectives for appearance and the budgets for application. There is a fairly wide range of costs for the different types of systems. The inquirer should contact product manufacturers listed on the PDA membership list to get specific recommendations for his project.