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Problem Solving
INDUSTRIAL FLOORING: ADVANCES IN MATERIALS AND APPLICATION
Thomas J. Murphy Abstract: This article focuses on the state of the art of industrial flooring. Tradition technology and application techniques are reviewed. Installation of these floors has improved modestly but they continue to be time and labor intensive. Improving the speed of installation has necessitated the need to look at different chemistries and application techniques. Polyurea systems can address installation speed and functionality in many cases, but cannot be expected to address all applications. INTRODUCTION As an overview of the state of the art of industrial flooring technology, it is beyond the scope of this paper to review the methods and developments in surface preparation. It is however, emphasized that regardless of the chemistry and application techniques discussed here, the most critical step in the successful installation of any flooring system is good surface preparation. Standards and guidelines have been established for surface profile of concrete and means by which to achieve the desired results. 1 TRADITIONAL FLOOR TREATMENTS
Although concrete provides most of the industrial flooring substrate, it does not serve
as a good long term wear surface due to the nature of the product. Continuous traffic
will cause concrete to dust and spall. Exposure to impact, vibration and heavy loads
will result in cracks and potholes.2 Moisture and chemicals will penetrate the porous
surface and can cause a variety of physical and chemical changes to the concrete itself.
In extreme conditions these chemicals may eventually pass through the concrete to
contaminate the ground or aquifer system. In addition, clean industrial environments,
such as food, beverage and pharmaceutical applications, require finished concrete to
seal the surface preventing contamination from the substrate.3
A variety of floor finish treatments have been used, including wood block, rubber,
linseed oil treatment and silicate concrete hardeners, each of these has met certain
objectives but cannot be considered as an ideal surface for the broad based industrial
market. Wood block was widely used in heavy manufacturing because of its ability to
withstand impact, absorb oils and maintain a relatively skid resistant surface.
Wood, however, will deteriorate in these conditions and replacement of these blocks
required excessive labor and plant shutdown. Rubber floors also handle impact
conditions and are slip resistant in wet environments, but they are susceptible
to tears and gouges. Rubber flooring is most frequently installed in sheets
leaving the seams as weak points, which may create undercutting, disbondment
and concrete contamination. Concrete treatments such as linseed oil and sodium
silicates provide a denser concrete surface that is less porous than untreated concrete.
However, these treatments do not protect concrete over the long-term in heavy industrial
applications.
Penetrating concrete sealers and hardeners provide minimal wear resistance, thus coatings which yield a build of 6 to 20 mils have been universally accepted as the treatment for light duty industrial or warehouse applications. Epoxy and urethane coatings have been widely used due to the overall performance and economy of their application. Coatings can improve the facility lighting through high reflectivity and brightness and have a smoother finish that can help with facility maintenance. These one or two coat systems are installed in relatively short time frames with either roller or spray application. Average millage of application is 8-15 mils and the durability and service life can vary from one to five years depending upon the traffic. Epoxy technology has improved over the past ten years making 100% solids, zero VOC and low odor the standard. Polyurethane technology, on the other hand, is primarily solvent based with only a few premium products available that meet the 100% solids, zero VOC and low odor benchmark set by epoxy products. One of the disadvantages of coating applications is their inability to handle heavy traffic, impact and long-term wear.4 For this reason, high build heavy-duty systems have been installed as either self-leveling slurry or mortar systems. The amount of material, installation time and cost of application is significantly higher than coatings. Mortars are selected for surfaces that may require thermal shock resistance due to steam cleaning or process related temperature changes. Mortars are also used in conditions with heavy traffic, steel wheel carts, or if the concrete requires "resurfacing". By modifying the type and amount of aggregate that is added to the resin, a slurry or self-leveling system results. Self-leveling systems are much more resin rich and will, by their nature, follow the profile of the concrete. These systems are ideally suited for aisles that will have rubber wheel traffic and on surfaces where the concrete to be finished is in relatively good condition. Maintenance and repair of these systems is also dependent upon the conditions of use, but most situations only require the recoating of these systems to maintain both a functional as well as aesthetically pleasing floor. Mortars and self-leveling systems are available in a variety of chemistries. Bisphenol A based epoxy is the most widely used binder resin due to its typical physical properties and relative cost. Epoxy can be formulated to meet specific application demands such as cure time, finish texture, color, gloss, viscosity and chemical resistance. This flexibility in chemistry has made epoxy a workhorse product as a primer, binder resin and topcoat. Novolac, vinyl ester, or other resins can be substituted in these systems for more chemical resistant applications. A relatively new innovation in epoxy chemistry is the formulation of internal flexibility. These flexible epoxies do not use plasticizers as a means interfering with full cross linking, as this technique will result in an embrittling of the epoxy over time.5 Instead, the polymer backbone is designed with lower cross-linking functionality.6 7 Application of this material in the industrial environment has proven to be effective in areas with heavy impact or in areas that may experience rapid temperature changes. Broadcasting aggregate into the flexible epoxy provides an excellent wear surface. Unlike polyurethane elastomers used for waterproofing applications, the flexible epoxies provide outstanding adhesion to the concrete and the aggregate in the wear course.
Although epoxy mortars have proven to be an excellent material for heavy industrial applications, the overall time and labor required to install these systems is considered a disadvantage in fast track projects and plant shut down schedules. Mortar systems are installed by blending the epoxy resin with the selected aggregate and troweled onto a prepared and primed concrete surface. Large application areas allow installers to use power tools such as power screeds for more rapid placement of the mortar, and power trowels to compress and compact the mortar. Although this process can be scheduled and manned efficiently, the mortar must be allowed to cure for 8-20 hours prior to finishing the application with grout and or topcoats. These finish coats must cure for 12-24 hours prior to returning the areas to service. This "built-in" timetable necessitates a 3-4 day minimum schedule for small areas and more time for larger facilities.
Improving the speed of installation and decreasing the return to service time required the review of different materials. Another relatively young development in chemistry of flooring systems is the urethane mortar systems. This complex chemical reaction between cement and urethane involves isocyanates, polyols, calcium silicate and calcium hydroxide. The benefit this technology brings is relatively quick turn around time. These systems are available in either slurry or mortar consistency and can be installed within a 24-hour window. Installation techniques do not vary significantly from those utilized to install epoxy flooring and no special equipment is necessary. It is the faster cure time and few installation steps that account for the quicker installation time.
Methyl methacrylate (MMA) chemistry has also been used due to the speed with which it cures and can be installed. This technology has a broad installation temperature range and has good color stability. MMA systems have been successfully used in both decorative and industrial applications. MMA is a free radical catalyzed polymerization reaction. Moisture in the area and in the concrete can interfere with this mechanism by scavenging the free-radical catalysts. Odor has also been a major problem with the installation of MMA. Both in new construction and renovation environments, airflow and ventilation must be maximized to prevent adverse affects on building occupants and other trades.8 NEXT GENERATION Installation speed and short turn around times are becoming increasingly important in the construction industry and especially on-going manufacturing. Heavy duty flooring systems that require multiple step application with overnight cure between applications are by definition time consuming to install and labor intensive. Speed of application without sacrificing performance is the driving force of the flooring industry. Epoxy, MMA, and polymer modified cement mortars require the installation of heavy-duty flooring using traditional manual techniques. Either the labor process or the cure rate of the chemistry employed limits the rate of installation. The ability to utilize polymers that have set times shorter than 1-2 hours requires the use of different application techniques. Spray application of paint and coating materials brings efficiency and speed to the coating process. Utilizing this application process has opened the door to the use of faster polymeric chemistries for both coatings and industrial flooring applications. There are currently a few unique systems available which improve the efficiency of application in combination with the speed of the polymerization. In an effort to build upon the advantages proven by epoxy mortar flooring, the system has been modified to be applied with the aggregate in a single step "liquid" application to provide a ¼" heavy-duty industrial floor. The principal difference and advantage over slurry type epoxy systems is the accelerated rate of cure and the use of pumps and spray delivery equipment. The combination of a faster chemistry and quicker installation often allows for rapid turnaround and reduced labor cost. It must pointed out that although the application of material using spray techniques can significantly decrease the time of installation in wide open areas, masking, over-spray control, and working in more confined areas may not enjoy any time savings. Coupled with a more rapid installation process, the speed of the chemistry can be taken to an extreme. Polyurea and polyurethane polymerization reactions are measured in seconds and minutes versus hours. Both of these technologies have been utilized in spray applied membrane applications. 9 10 The physical and chemical properties of each of these options are comparable. Comparison of Polyurethane and Polyurea Physical Properties
Comparison of Polyurethane and Polyurea Chemical Properties
The key differences between these two technologies are based upon the fact that polyurethane is a catalyzed reaction rendering it susceptible to problems due to both moisture and temperature during application.11 Polyurea has a much broader application temperature range and can be installed as low as -20 degrees F. Both of these base chemistries produce a strong, abrasion resistant flexible membrane material. Spray application of these materials is widely used in waterproofing, lining and steel coating applications.
Parking Deck
The inherent flexibility and moderate chemical resistance of polyurea has made it an excellent selection as a membrane for secondary containment, mechanical equipment rooms and parking decks. 12
Secondary Containment
Extending the application of polyurea chemistry into more aggressive industrial environments requires modification of the system to handle more abrasive conditions. Although parking decks do not experience the same conditions as heavy industrial plant floors, some parallels can be drawn. Parking decks require a membrane material to provide crack bridging and waterproofing, as well as a wear surface that provides an impact resistant, skid-resistant, and abrasion resistant surface. Industrial applications can also utilize a membrane for crack bridging and thermal shock resistance in combination with a more durable, slip resistant wear course. Polyurea has been successfully installed in these applications using a rapid set spray applied membrane over a prepared and primed concrete substrate. Over this membrane a second application of "textured" polyurea provides a slip-resistant wear surface. 13 As an alternative, a slow set (3 minutes) polyurea formulation can be used for applying the membrane into which an aggregate is blown in immediately after application. When using this later method, it is recommended that a polyurethane topcoat be applied to "lock" the aggregate into the system and to enhance the color stability and aesthetics of the system. The use of polyurea spray applications in heavy industrial environments needs to address the following conditions:
The inherent flexibility, tensile strength and abrasion resistance of polyurea cover most of these points. The potential for gouging of the elastomeric material must be addressed with a harder finish treatment. A second step application of a slow set polyurea variation or a fast set epoxy allows for the introduction of aggregate to form the skin or armor for the system. In chemical exposure conditions it will also be necessary to apply the finish coat using the best available chemical resistant products. A Novolac epoxy, for example, may be required in high sulfuric acid conditions such as battery plants or wastewater treatment facilities. In food plants, on the other hand, a highly chemical resistant urethane finish can be specified. DETAILS The successful installation of any flooring system is dependent upon attention to details, transitions, terminations and repair ability. Systems that cure rapidly can present some unique problems that must be addressed for overall success. Fast set chemistries have been suspect when applied to concrete surfaces due to the fact that they do not have time to penetrate into the concrete substrate. For this reason it becomes more import to properly repair the surface, remove contaminants, and to apply a primer that more easily penetrates into the concrete. A polyurea water-based primer has a longer pot life, thus penetrates into the concrete and can be recoated within 2 hours. Using an epoxy primer is also possible but the epoxy must cure to a tacky state to prevent the isocyanate in the polyurea from scavenging the epoxy amine. When using these primers, adhesion of the polyurea system to concrete has been measured to exceed the concrete tensile strength.14 Repairs are an equally important issue in providing a long lasting heavy industry flooring system. Regardless of how durable the system might be, there are situations where excessive abuse will result in areas that need repair. A heavy impact that exceeds the tensile strength of concrete may in fact not fracture the system but instead will crush the underlying concrete leaving the system intact but not bonded. Polyurea, like epoxy systems, bonds very well to itself when properly prepared and primed. Therefore, repairs can easily be preformed using a brush grade, long pot life (5 minutes) formula. After removing all affected areas and repairing the underlying substrate if necessary, a special tack coat primer is applied followed by reapplication of the system using the brush grade version of polyurea (slow set).
Joints and cracks can easily be addressed with polyurea due to their inherent strength and flexibility. A self-leveling slow set version of polyurea is available for protection of control joint edges and filling routed cracks. This product has similar physical properties to flexible epoxies used for these applications but the area can be reopened for service one hour after installation.
Cove base and vertical applications with spray-applied polyurea have been addressed in tank lining and waterproofing applications. A small radius cove may be applied using a flexible sealant prior to coating the floor and wall with the polyurea membrane. This allows for easier cleaning and fewer voids to harbor dirt. As an alternative, a pre-coat of polyurea may be applied to the cove area to increase the build at the vertical angle.
Terminations at edges and drains require the same treatment as other flooring systems. Edges to be terminated must be saw cut and keyed to allow for a strongly bonded straight edge. Floor drains must be keyed to the edge of the drain, not carried over the lip. This allows the drain to function properly while the polyurea system flexes with the drain movement.
Given the obvious advantages of fast cure chemistries such as polyurea, the initial inclination is to use these products for all applications. Although fast cure and fast application techniques can dramatically reduce installation schedules for large open areas, situations with machinery, piping, and other mechanical details will require pre-installation masking, protection and detailing which may exceed the time savings of spray application. Bond strength is also a concern with fast chemistry of polymerization. The substrate must be carefully prepared and penetrating primers must be used to maximize the concrete bond. Intercoat adhesion is also suspect when topcoating a polyurea with a different chemistry. When considering multicoat systems, installers must adhere to manufacturer's recommend products and recoat windows. Aesthetics of a fast system may suffer. The advantage of using fast set materials to apply high build systems and continuous floor to wall application also presents a disadvantage. Installation contractors do not have the luxury of fixing small inconsistencies in the material surface and the products themselves are so fast that they will not self-level. SUMMARY Overall, there are a number of flooring products and systems that work well in heavy industrial environments. Traditional epoxy systems have proven over time to provide an excellent wear surface for most facilities. Due to the requirement of faster turn-around times, a number of alternative polymeric systems have been developed. Methyl methacrylate and polymer modified cement systems have addressed the issue of installation time but lose performance properties as a trade off. The ability to utilize spray and pump application allows for the utilization of polyurethane and polyurea chemistries. These systems set within minutes, not hours, and entire installations can be realistically returned to service within 1 to 2 days. Polyurea systems have a broader range of application temperature and can be modified to handle the details required for proper flooring installation. There are some industrial flooring applications that will benefit from the advantages of polyurea technology. No technology, chemistry or application technique can satisfy all environments. Polyurea industrial flooring offers one more option. REFERENCES 1. ICRI/SSPC Surface Preparation Standards 2. Johnson, Robert. Understanding Volume Changes of Concrete Before Resurfacing. Concrete Repair Bulletin, September / October 1998. 3. Murphy, Thomas. Selecting a Coating. Plant Services, 1999. 4. Murphy, Thomas and Durig, John. Selecting a Flooring System: Considerations for a Seamless Flooring System. Plant Services, June 1998. 5. French, Gary. Comparison of Flexible and Rigid Epoxy Systems for Concrete Protection. Concrete Repair Bulletin, January/February 1999. 6. Durig, John. New Flexible Epoxy Technology. SSPC Coatings for Asia 1999, September 1999. 7. Durig, John. Internally Flexible Epoxy. Concrete Repair Bulletin, November, December 1996. 8. Silikal Acrylic Resin Flooring Systems. 1992. 9. Primeaux II, Dudley J. Polyurea Spray Technology in Commercial Applications. 60 Years of Polyurethanes: International Symposium and Exhibition. 10. Whipple, Ron. The Next Step in Floor Protection. Plant Services, September 2000. 11. Hare, Clive H. A Review of Polyurethanes: Formulation Variables and Their Effects on Performance. JPCL, November 2000. 12. Primeaux II, D. J. and Hillman, K. M. Polyurea Elastomer Technology: Bridging the Gap to Commercial Applications. Polyurethanes EXPO '98, September 17-20, 1998. 13. Primeaux, Dudley J. Application of 100% Solids Plural Component Aliphatic Polyurea Spray Elastomer Systems. 2000. 14. Huntsman Corporation. Polyurea Spray Technology Information (1004-996). Technical Bulletin, 1996.
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LIMITATIONS OF SPEED