Everywhere you look, you see flat surfaces. Some of those surfaces are floors. Some of those floors have functional problems. Some of the problems have been plaguing you for some time. You want answers, you have questions.
Those are the major premises behind this question and answer session. Imagine yourself, if you will, sitting in a technical session about flooring at a conference. There is a panel of experts seated at the table in front of the room. Imagine them fielding questions from the audience.
We contacted three well known and respected suppliers to the flooring industry for the technical session. Let me introduce you to our panel for this 1997 edition of the flooring Q&A. They are Mark Moran, Director of Rock-Tred, Gary Hall, Eastern Regional Manager of Sauereisen Specialty Cements, Hank A. Bruflodt, Director of Technical Services of Floor Seal Technology, Inc., and Charlie Bloss, Southeast Regional Manager of Floor Seal Technology, Inc. So, let's get on with the purpose of the session.
Q1: We frequently hear the term 100% solids used to describe industrial flooring products. What percentage of industrial products are actually installed as 100% solids? What are these products?
Hall: Probably less than half are 100% solids. Solvents and reactive diluents improve working characteristics, flowability, working time, and reduces cost. However, the 100% solids materials are less permeable, more environmentally friendly, and meet EPA VOC limits. Many times contractors add diluents so systems designed to be 100% solids end up being something else.
Bruflodt/Bloss: With the VOC requirements that are in place, the percentage of this material that is installed is increasing. The term '100% solids' refers to the exclusion of volatile organics from a product. The 100% solids material do not release VOCs into the atmosphere. The current laws dictate that each State formulate their own VOC requirements. However, this could, at some time, become a national requirement that impacts the entire flooring industry.
Q2: When an industrial flooring product is said to cure, what does that really mean? When does the curing process actually stop or reach its completely cured state?
Bruflodt/Bloss: A product is cured when the chemical reaction is complete. This is not to be confused with drying which is generally much quicker. A polymer flooring material may dry in a matter of hours and not completely cure for weeks.
Hall: Cure refers to the chemical reaction that takes place when the components are mixed. The reaction rate determines working time and cure time. There are two stages to curing. The first—called hardening—involves reactions between resin and hardener. Once the mix is no longer fluid or plastic, cross-linking becomes the dominant reaction. Novolac resins harden and cure at exponentially faster rates than bisphenol formulations. Complete curing may require a month or longer. In general, cure rates are directly proportional to temperatures. The cure rates for different formulations for low or high temperatures vary accordingly.
Q3: Why do different products have different cure times?
Hall: Reaction rates determine cure times. More reactive molecules speed up the reaction rate and reduce the cure time. Solvents and diluents slow the reaction rate. Even though there are thousands of combinations of resins, hardeners, solvents, and diluents, correct stoichiometric ratios are absolutely critical in achieving the desired results.
Bruflodt/Bloss: Products have different cure times because of different chemical compositions. Product literature from any manufacturer specifies the drying and curing times and those parameters must be budgeted into the course of installation.
Q4: Do all products cure by the same chemical process?
Bruflodt/Bloss: No. There are several different curing processes: exothermic, endothermic, atmospheric reaction, and curing by evaporation, to name a few. Again, it is important to understand the necessary curing process the product manufacturer requires and build that time into the total project installation time.
Hall: No. Some reactions are simple addition reactions, others are condensation reactions, some are influenced by ultraviolet light. Even within a generic class of resin there are different reaction routes possible.
Q5: Why are different products able to cure in cold temperatures and others cannot?
Moran: Certain products cure in cold because they are inherently more reactive than products that require heat to cure them. Heat is a form of energy and some products do not cure at low temperatures because there is insufficient energy available to complete the reaction. In general, a given product cures less rapidly at lower temperatures.
Hall: The choice of hardener and resin determines whether a material cures at low temperatures. Highly reactive resins and hardeners cure at lower temperatures. Faster curing systems have lower chemical resistance. The problem is one of balancing cure temperature with pot life, chemical resistance, viscosity, and workability.
Bruflodt/Bloss: The nature of the polymer used dictates how the product is to be properly cured. Therefore, polymer coating product manufacturers have various chemistries for particular climatic conditions.
Q6: Why do certain coatings, when used outdoors, eventually chalk and turn brittle? Are there any products that can be used outdoors that will not chalk and turn brittle?
Hall: Ultraviolet light in sunlight degrades the resin and breaks the chemical bonds. This leaves a chalky film of fillers and exposed pigments on the surface. The film weathers and exposes more resin to degradation. Acrylics and aliphatic urethanes have the best UV resistance but may not be suitable for the expected chemical service. Adding UV blockers and inhibitors improves UV resistance.
Bruflodt/Bloss: Some coatings chalk and turn brittle outdoors because of their reaction to ultra-violet light. Most epoxies are not very UV stable. The best material to use in this situation would be an aliphatic urethane that is not affected by UV light.
Moran: Coatings chalk and turn brittle because of a reaction between the polymer matrix and ultraviolet radiation, moisture, oxygen and other substances. Thermal cycling also affects the physical properties of some coatings. Aliphatic urethane coatings can be used outdoors and keep their colors and physical properties.
Q7: What exposure temperature extremes should I be concerned with when installing an industrial flooring system?
Bruflodt/Bloss: Most, if not all, coatings should be installed when the temperature is between 55 and 90 degrees Fahrenheit. This wide range of acceptable climate should not present problems for most installations. However, watching the climate in the building prior to, during, and after installation is an obviously good practice to minimize problems with drying and curing.
Moran: Most 100% solids systems should be applied between 55 and 85 degrees Fahrenheit to achieve optimal performance with acceptable cure times. Cure rate varies directly with temperature and the cure time will vary from the spec sheet during temperature extremes. In colder temperatures, the coverage of a 100% solids material will be reduced because of the associated increased viscosity. Most manufacturers have cold weather formulations.
Hall: Temperature limits depend on formulation and chemical service expectations. The degree to which chemicals reduce the temperature limits cannot be predicted. Testing is mandatory. Resins begin to degrade above its glass transition temperature (T-g-) and regardless of claims to the contrary, the T-g- is the effective dry heat limit.
Q8: Why do some products bond to concrete and to each other better than others?
Moran: Certain products bond because of an ability to penetrate and mechanically "grip" the concrete substrate. Increasing the concrete surface area by shot blasting or acid etchings increases the bond strength between the primer and the concrete. In general, primers are of a lower viscosity than are products used to "build up" the floor. Bonding between coats is more chemical than mechanical. That is why a coating system specifies an open recoat time beyond which the previous coating surface needs to be reactivated by sanding or blasting. The more similar the products, the stronger the chemical bonding between coats.
Hall: The question assumes all concrete surfaces and coatings are equal—a totally fallacious assumption.
The most common cause of failure is improper and inadequate surface preparation. Even with properly prepared concrete, generic classes of resins have different degrees of inherent adhesion. Even the surface strength of the concrete affects the bond. If the resin does not adequately "wet" the surface, adhesion will be lower. Solvated primers, low surface profile amplitude on the concrete, and laitance interfere with adhesion to concrete. Bonding to an existing coating depends on compatibility, surface hardness, profile, solvent release, and numerous other variables.
Bruflodt/Bloss: Again, the chemistries of various products dictate the bond integrity of each. The manufacturer of the product can specify the best polymer for a particular application. If the substrate is properly conditioned to accept a polymer coating, it must meet a "minimum" tensile strength of 100 psi to be acceptable by ASTM standards. Most coatings installations easily exceed this minimum.
Q9: What are the differences between products that mechanically bond and those that chemically bond?
Hall: Coating can bond to other coatings either mechanically or chemically whereas the bond to concrete and steel is purely mechanical. Detailing the differences between coatings involves understanding an entire branch of chemistry. I can recommend several excellent reference books.
Bruflodt/Bloss: Concrete is complex in terms of its long-term chemical interactions. It gets stronger with age. To the best of our knowledge, coatings depend on mechanical bonds as a result.
Moran: Mechanically bonding products have lower viscosity that allow better penetration into the substrate. Chemically bonding products need a slow enough cure time so that reactive sites remain open to chemical bonding to the next coat.
Q10: Salt water, sunlight, spilled beverages, and foodstuffs eat away at the concrete in my amphitheater. What should I look for in an industrial coating that will withstand this kind of exposure?
Bruflodt/Bloss: The UV coating in this application should have chemical-resistance to acids and base materials and, of course, UV resistant.
Moran: Check the technical data sheets for the coating to verify that it is suitable for the anticipated environment. The 100% epoxies withstand these exposures but yellow in direct sunlight. A top coat of aliphatic urethane takes care of yellowing. Chemical resistance increases with more highly functional polymers with their increasing number of reactive sites per monomer molecule.
Hall: Sunlight does not eat away at concrete. Other weather elements do, though. Only testing ensures that a system withstands the plant environment. Each generic class of coating is suitable for specific exposures. The physical properties of a coating—like mechanical strength—do not correlate with chemical resistance. Manufacturer's resistance charts are guides, not definitive answers. ASTM test methods only tell how to run the test, they do not set exposure times or pass/fail criteria. Since each manufacturer selects their own exposure times and temperatures, allowable weight and strength loss limits, you must test in-house.
Q11: To what extent is water vapor transmission through on-grade concrete slabs a problem? Why the seemingly sudden concerns?
Moran: If water vapor transmission through the concrete exerts enough pressure, it can prevent adhesion of a non-breathing 100% solids coating. Use ASTM D 4263, Standard Method for Indicating Moisture in Concrete by the Plastic Sheet Method to check the concrete. Concerns seem sudden because more people have just become aware of the problem. The floor coatings industry has been aware of this problem for years.
Hall: It is a problem, but not a new one. NACE, ASTM, and SSPC, among others, have been dealing with this issue for years. The problem is a lack of concern on the part of contractors, engineers, architects, and owners who lack the required knowledge and experience, who don't care, or who are trying to save money. When the coating fails, the coating manufacturer gets the blame when, in fact, the application should never have proceeded without remedial action on the concrete. The sudden interest is probably due to environmental concerns, a desire for maximum service life without recoating every two to three years, and attention being paid by contractors, specifiers, and manufacturers that got burned in the past.
Bruflodt/Bloss: All concrete slabs emit some measurable volume of moisture vapor regardless of the age, elevation, or location of the building. When this volume exceeds the maximum tolerance of a floor covering or polymer coating, failure occurs. Statistically, moisture-related failures occur within six months to two years after installation. This usually means that the operations taking place on top that floor must stop in order to correct the problem. The costs directly attributable to floor system failure, down-time, and establishing blame represent billions of dollars for Americans each year.
The reasons for the sudden concern is obvious: The whole purpose of erecting a building is to put your "stuff" inside of it. That "stuff" resides on the floor system. If the floor system fails--resulting in bleeding adhesives, curling tiles, bubbles in vinyl, and fluid-filled blisters in coatings—then you have to move that "stuff" off the floor to fix it. If it isn't properly treated, then history simply repeats itself. Its a very graphic and expensive problem.
Q12: What is the root cause of water vapor transmission through on-grade concrete slabs?
Moran: Water vapor transmission through on-grade concrete floors occurs when the relative humidity is higher below the slab than above and there is no moisture barrier below the slab. Water vapor rises through the capillaries of the concrete and immediately dissipate into the ambient air leaving the surface to appear as dry.
Hall: The problem is not only with vapor. Hydraulic pressure is also a concern. Both water and water vapor permeate a porous material like concrete that has an apparent porosity of 16 to 17%.
Bruflodt/Bloss: The root cause is eloquent. Most people thought "hydrostatic pressure" or "capillary action" inside the slab pushes water to the surface. While this can be a problem in some cases, it fails to explain why suspended slabs also have moisture-related failures. Actually, the root cause is a subtle but powerful pressure differential that exists between the substrate and room interior. At any given temperature and relative humidity, there is a static amount of pressure expressed in psi. The temperature and internal humidity of concrete creates a static pressure that is often twice as high as the static pressure inside the room. The lower pressure inside the room literally sucks water vapor out of the slab.
The same principle of physics is also responsible for creating thunderclouds that suspend millions of tons of water in the air. This is the "engine" of vapor emission. The volume of moisture that can reach the surface is basically predicated upon the slab's porosity. The more porous it is, the more volume that can be drawn out.
Q13: What measures should one take one an existing slab to make the problem disappear permanently?
Moran: Use a coating that breathes. This is not the best solution because it can compromise chemical resistance and water vapor still passes through the concrete. Use fast-setting primers that bond well to the concrete before enough water vapor is transmitted to disrupt the bond. Avoid direct sunlight on the slab. Leave heating units, air conditioners, dehumidifiers off prior to and during the coating application, allowing the humidity above and below the slab to equilibrate.
Hall: It may not be possible to eliminate the problem on an existing slab. Some situations are correctable, others are not. Involve a qualified, professional that specializes in this type of remedial work.
Bruflodt/Bloss: Bringing vapor emission into compliance requires very careful engineering. Most products purported to do this are actually waterproofing agents that keep water from getting into concrete but have little, if any, effectiveness in controlling gases escaping from the slab. Instead, vapor emission control is effective when using products that buffer the pressure differential at the surface which is the root cause of emission. Treating the cause is more effective than treating the symptoms. The most important qualification of any product for this purpose isn't the claims made in the literature, but in the long-term history of the product and manufacturer in real-world applications. If moisture control was as simple as many people claim, it would not represent one of the largest problems in the industry today!
Q14: What measures should one take one before pouring a new slab to make the problem disappear permanently?
Moran: Install a moisture barrier such as a plastic membrane before pouring the slab.
Hall: Install a vapor/water barrier between the water source and the bottom of the slab. Do not penetrate, cut, or puncture these vapor barriers. Extreme cases may requires some sort of drainage as well.
Bruflodt/Bloss: A proper vapor retarder is the first line of defense. Then, a slab with a low and carefully-controlled water/cement ratio, followed by a full wet-curing are the basics of creating a vapor-compliant slab. From there, it gets extremely complex. That is because concrete will have to dry. Typically, it takes a minimum of 70 degrees Fahrenheit, a maximum of 40% relative humidity, and a steady 15 mph wind to dry slabs at a rate of 1 inch per month. In many cases, the slabs poured in America don't start really drying until the building is finished, the floor is in, and the HVAC system activated. Is it any wonder why floor system failures are so prevalent? The biggest problem with vapor emission problems isn't physics, but people's construction schedules.
Q15: Increased productivity sometimes relies on the use of exotic acids and other chemicals. What should one use on a concrete floor to make it water- and chemical-resistant while simultaneously accommodating a shifting and cracking slab?
Bruflodt/Bloss: A fibermat can stabilize the slab and then a vinyl ester or novalac epoxy material can provide for chemical resistance. Once again, it is best to discuss the condition of the building with the coatings manufacturer for the best recommendation to control for this condition.
Moran: Use an elastomeric (flexible) 100% solids material to fill joints and cracks in the slab. Use a coating system that withstands the anticipated chemicals, Standard epoxies exhibit good overall chemical resistance. Novolac epoxy coats can be used for more stringent demands. Always coat a test area that can be subjected to actual workplace chemicals.
Hall: Manufacturer's produce a variety of coatings because there is no single universally chemical resistant coating. Rehabilitating a cracked and lifting floor is difficult and expensive, but it must be rehabilitated before attempting to coat it. A shifting floor will cause any coating to fail. In some situations, a crack bridging coating system can accommodate movement of 50 mils or less in the plane of the concrete surface. No flooring system withstands uplifting concrete.
Q16: Our die shop has a wooden floor on a concrete substrate. What should we be doing to ensure that it remains functional for years to come?
Moran: Very few 100% solids systems will be flexible, yet hard enough for this application. Remove the contaminants and sealers down to bare wood and coat with a high solids (greater than 40%) urethane coating. Three coats of urethane would be ideal.
Hall: We do not deal with wooden floors. It may be better to replace the wooden floor with refractory concrete or brick.
Bruflodt/Bloss: For wood floors in industrial applications, watching the grit that settles on the surface would be the most obvious thing to do. Fines that get ground into wood floors destroy the surface finish and eventually destroy the aesthetics and performance of the floor.
Q17: It would seem that properties like skid-resistance and cleanability are mutually incompatible. How should go about finding the ideal balance point between the two?
Hall: The best approach is to first establish the required coefficient of friction as measured by a James machine. The static coefficient should be 0.60 at a minimum. Frequently cleaning methods require changes like eliminating mops and squeegees in favor of more aggressive and extensive cleaning methods. Test the floor with various shoe materials at both wet and dry conditions.
Bruflodt/Bloss: The best way would be to try several test areas and experiment with skid-resistance and cleaning. Plan ahead and consult with the polymer floor manufacturer about the best material for a particular application. Let them know exactly what the floor will be used for and how it will need to be maintained. The manufacturer can prescribe the best type of product for this application. Realizing that the wrong product was installed for the floor's use simply because it was inexpensive might be more expensive yet.
Moran: Finding a happy medium can be difficult. Safety concerns usually dictate the degree of slip resistance required. Encapsulating aggregate within a 100% solids epoxy system provides both slip resistance and a cleanable floor. The quantity and size of the aggregate determines the slip resistance. There are also a variety of anti-slip high solids coatings that use other additives to yield slip-resistant cleanable floors. The more slip resistant the floor, the greater the probability that a pressure washer will be needed to clean it.
Q18: Speaking of balances, tell me about chemical-resistant floors and esthetically pleasing colors.
Moran: Standard and Novolac epoxy floors are available in virtually any color imaginable. Using pigmented aggregate blends with clear epoxy coatings can provide multi-colored aesthetically pleasing floors.
Hall: Esthetically pleasing is in the eye of the beholder. Certain colors are known to fade and discolor. Blues are difficult to maintain in their original shade and hue. Some resins take on a characteristic color when exposed to particular chemicals, like Novolac resins turning reddish-brown from strong sulfuric acid exposure. Three chemicals could discolor a coating to three different shades. Make your specifier and installer aware of the chemicals. It is unrealistic to think a floor subjected to aggressive compounds won't discolor. The safest colors are grays and reds.
Bruflodt/Bloss: Polymer coating manufacturers have all types of products for specific environments. Discuss with the technical agents the kind of chemicals that might spill on the floor. They should be able to specify a solution. As far as colors and patterns are concerned, each manufacturer has their own line of finishes that you can choose and specify.
Q19: One part of our facility handles semiconductors and another handles solvents. What is available in skid-resistant antistatic or conductive flooring? Can we use the same flooring for both areas?
Hall: Non-skid dissipative or conductive coatings are problematic because the high points or aggregates that make it skid-resistant are also nucleation sites where electrostatic discharges occur. With time, the thin layer of resin over the aggregate wears away to expose the non-conductive aggregate. A conductive floor with non-skid aggregate has a higher conductance than a dissipative floor and more efficiently drain accumulated charges. Use a conductive, non-sparking Novolac floor in the solvent area and a dissipative bisphenol A coating in the semiconductor area.
Bruflodt/Bloss: There are some very good ESD urethane products that afford chemical resistance, skid resistance, and excellent ESD properties. The main ESD characteristics that apply to both semiconductor manufacturing and solvent handling are body voltage generation and body voltage decay. The total ESD flooring system includes three distinct elements--the person wearing ESD footwear, the ESD floor, and a common ground point. If the floor and the person's footwear do not generate a static voltage and the voltages are rapidly dissipated, then the flooring material would be applicable to both areas. Some industries require the conductive resistance range as opposed to the static dissipative resistance range in areas with hazardous chemicals. However, the ultimate test is how fast the charges dissipate and whether the contact and separation of the floor and footwear generates a static charge. This is an example in which pre-installation testing, certification, and periodic recertification are essential in properly controlling electrostatic discharge.
Moran: 100% solids epoxy coatings are available in slip resistant, antistatic, and conductive versions. Use a conductive coating in the solvent room. Use an electrostatic dissipative coating in the semiconductor room. The electrostatic dissipative floor will not dissipate a charge or spark fast enough to prevent a fire. It just provides protection for materials that are sensitive to static charges.
Q20: Most flooring material, including concrete, are supposed to meet one or more ASTM standards. Aren't these standards nothing more than the minimum acceptable performance characteristics of the material?
Bruflodt/Bloss: The ASTM designations for performance standards are usually based on the collective wisdom and experience of those involved with the material or procedure in question. One can say the standards are minimal acceptable standards but, in reality, the standards ensure that people performing tests have solid guidelines and expectations that meet safety and performance criteria. Everything needs to have a scale of measurement, ASTM provides scales that everyone can understand and easily follow.
Moran: ASTM standards are not minimum performance standards. ASTM standards are proscribed methodologies for performing tests. They ensure that different testing entities acquire test data consistently. Refer to competitive literature regarding a flooring product to see which manufacturer's product is superior. When comparing product performance characteristics, make sure the same ASTM test was used.
Hall: Flooring materials may, or may not, meet ASTM standards. ASTM is a voluntary consensus organization and its published standards are not per se guarantees of performance. Some ASTM methods tell how to perform a test, others are simply specifications, others are guides on using a particular material. Concrete performance is more influenced by ACI codes. No coating standard published by ASTM or any other organization covers all the needed facets. Some standards cover physical properties, but not a single standard exists that establishes pass/fail criteria for chemical resistance. The standards that do establish performance criteria cover only ambient conditions prior to exposure when cured in an ideal manner by skilled technicians in a laboratory. They are woefully silent regarding post-exposure criteria.