Available Resinous Technologies
System performance (relative to the environment in which it is installed) depends greatly on the chemistry and flooring type selected for the application. Although there are a myriad of technologies used in the industrial coating industry, the most traditional and widely available include acrylic, epoxy, polyurethane, polyurea, polyaspartic, polyester, or vinyl ester.
CONCRETE HARDENERS OR DENSIFIERS
Concrete hardeners are usually sodium silicate, potassium silicate, lithium silicate, solutions or metallic fluorosilicates. Where hardeners have been used, the concrete will usually appear glossy and may be a grey to brown color. Hardeners used instead of sealers and for new concrete as well as existing concrete. These products typically improve with age. The Densifier actually crystallizes in the concrete accelerated by the general scrubbing of the floor or by concrete polishing. Over time these floors develop a very attractive gloss and are excellent for warehouse areas where cost is the first priority but appearance is also important.
ACRYLIC RESINS, also known as Methyl methacrylate resins and co-polymers, are used for waterborne coatings, such latex house paint. It is also used in adhesive formulations. Acrylics coatings - vary from extremely hard, brittle solids to elastomeric (rubber-like) structures to viscous liquids. These materials tend to have excellent water, weather and UV resistance. In addition, they are stable under moderate thermal shock conditions, but provide lesser mechanical strength, chemical resistance, and adhesion compared to alternate systems.
MMA (Methe Methacrylate)
MMAs are fast curing acrylic coatings that are resistant to weak acids and alkalis and have moderate resistant to solvents. Fast curing is a big advantage of MMAs, especially at low temperatures. At room temperature MMA has a working time of 10 to 15 minutes and reaches a full cure in 1 to 2 hours. MMAs are two-component systems in which the MMA resin is mixed with a solid powder initiator. After mixing, curing of MMAs is inhibited by oxygen in the air. Manufactures overcome this problem by including paraffin wax in the resin. During cure, the wax rises to the surface forming a protective barrier.
When applying as a resurfacer it is important to use the continuously graded aggregates from the manufacturer to avoid trapping air within the resurfacer. MMAs must be applied to dry concrete because moisture interferes with binding. MMA have excellent intercoat adhesion and are resistant to ultra-violet light. Their maximum surface temperature is normally 140 degrees F. MMAs release a strong odor and are flammable, so it is important to ventilate the work area.
Epoxy resins are thermosetting products known for excellent surface and sub-surface adhesion, mechanical properties, and chemical resistance. Epoxy resin systems are made up of an epoxy resin and a curing agent (also called a hardener or catalyst). Many epoxy products also contain additives such as organic solvents, fillers such as fiberglass or sand, and pigments.
When epoxy resin systems are used, single molecules (monomers) of the epoxy resin chemical and the curing agent combine to form long chains of molecules (polymers). As the mixture "cures," it becomes a hard polymer. Some epoxies cure in a few minutes at room temperature. Other epoxy systems need additional time or heat to harden. The characteristics of hardened epoxies (such as whether they are firm or flexible, or resistant to heat or chemicals) depend on which epoxy monomers, curing agents, solvents, and fillers are added.
There are two primary epoxy resins A epoxy resin which is a cost-effective, general-purpose resin which demonstrates excellent alkali resistance, good acid resistance and fair-to-good solvent resistance.
BISPHENOL F epoxy resin is a low-viscosity material which provides excellent alkali resistance and offers improved acid and solvent resistance compared to BISPHENOL A.
While there are few epoxy resins that are suitable for application, there are literally hundreds of epoxy curing agents. As a result, epoxies can be formulated to have a variety of physical properties, which makes it difficult to generalize their chemical resistance as a polymer coating. Cure rate of epoxies is affected by temperature and should not be applied with temperatures under 32 degrees. Epoxies have limited service temperatures and generally soften with temperatures over 150 degrees. They are also not resistant to ultraviolet light and will yellow with age.
The hardened, finished polymers are almost non-toxic; it is exposure to the uncured resin components that can be harmful. In a two-component epoxy product, the epoxy resin and the curing agent are packaged separately and must be mixed together just before being used. Each component can be hazardous. In a single-component product, the resin and the curing agent are supplied in a pre-mixed form.
Epoxy for concrete coatings generally come in one of three formulations. Solvent based, water based, and 100% solids. Solvent based and water based tend to be most commonly used for DIY applications due to their ease of application and long curing window after catalyzation. 100% solids formulations while more difficult to apply are more cost effective when comparing cured thickness and can be applied at much greater thicknesses allowing the material to self level.
100% solids epoxies are the most popular form of epoxy. The percent solids describe the amount of solvent in the product. In this case there is no solvents or liquid fillers of any kind. As a result these epoxies offer odorless installation. They cure exclusively by chemical catalyzation between the parts. What is surprising for some is that 100% solids epoxy are normally 97% plus solids but typically have the addition of bonding additive, leveling agents or other additives to aid application. As a result not all epoxies are equal.
Solvent Based Epoxies can vary significantly from one another. What holds them together is there use of solvents to aid in application, adhesion and/or leveling properties. They normally range from 30-70% solids are easier to apply than 100% solids epoxy and due to their solid content are much thinner after the solvent has evaporated and they have cured. Solvent based epoxies are generally more tolerant of petroleum based surface contaminants such as oil.
Water Based Epoxies are much the same as solvent based epoxy. There major difference is the use of water as the carrier rather than a solvent. With the increase government regulation and the harmful odors of solvent based epoxies these are much more popular. They are however a little more expensive than solvent based due to the technologies and can be a little more fickle for installation.
Flexible Epoxies are modified to provide elongation in addition to epoxies normal properties. Like Polyurea they can be used for joints and areas susceptible to movement like exterior slabs and multi story structures parking ramps.
NOVOLAC EPOXY - is fast curing and offers excellent protection for secondary containment where resistance to strong alkalis, acids, and solvents are required. Novalac epoxies have many properties of conventional 100% solids epoxy. Their difference lies in their polymeric structure. In chemical terms, novalacs have a higher cross-linked density than conventional epoxies. This makes them more rigid and chemical resistant, and allows them to withstand higher service temperatures. These properties lend themselves for use in chemical containment and battery charging areas. The downside to their higher cross-linked density is that novalacs are typically more viscous than conventional epoxies, which make them more difficult to apply.
Polyurethane resins, commonly referred to as urethane, are thermosetting or thermoplastic and demonstrate moderate chemical resistance and good resistance to diluted acids and alkali. Polyurethane resins generally offer moderate adhesion, but good resistance to shrinkage and good flexibility. Urethanes are a popular high-performance floor coating. They have many desirable properties, including fast cure times, high abrasion resistance and toughness, and good chemical resistance. They are typically the most resistant to water exposure, high humidity, temperature extremes, and fungus or mildew. Urethanes performed best when placed on dry concrete. Moisture inhibits the cure of two-component systems and can cause blistering of moisture-cured coatings because of its reaction with water generate carbon dioxide gas.
The first essential component of a polyurethane polymer is the isocyanate. Isocyanates can be classed as aromatic, or aliphatic. Important characteristics of isocyanates are their molecular backbone, solvent content, functionality, and viscosity.
Moisture cured Urethane
The “old stand-by” of urethanes are aromatic urethane also described as moisture cured urethane. Most commonly installed on wood floors, these urethanes are normally single components and dry through reaction with the moisture or humidity in the air. They can vary from 20% to 70% in solids with the remainder evaporating. As a result this percentage determines the dry film thickness once the solvent has evaporated. Still a good product for some applications its biggest drawback is its tendency to yellow over time due to low UV resistance and offensive solvent smell during application. Moisture cured urethanes are widely used because they perform well and offer the convenience of a one-component system but in aliphatic urethanes generally provide better performance.
Aliphatic Urethane is the next step urethane resin technology. It is still likely solvent based and a two component product much higher in percent solids. The primary performance difference between moisture cured urethanes and Aliphatic Urethanes is due to its chemical resistance being significantly higher. These products can resist solvents including methylene chloride (the active ingredient in paint stripper). The main reason that aliphatic isocyanates are used in making polyurethane coatings is the two-part product it is also UV stable holding its color with time.
Next generation or as they are commonly described “Odorless” Urethanes have come about as a result of the restrictions on solvent use in manufacturing facilities as well as government influence. There are numerous formulations that vary greatly in performance as well as cost. The difficulty is determining the quality. The main formulation techniques used to achieve odorless urethane is the use of water instead of aromatic solvents and the development of very high to 100% solids urethane products (80 to 100% solids). The increased desires for odorless polyurethanes have also led to the development of the sub group of urethanes known as Polyureas and Polyaspartics.
Developed roughly 30 years ago urethane mortars have increased in popularity from the original BASF’s “Ucrete” to more than a dozen major manufacturers producing them currently including Sherwin Williams, General Polymers, Tennant, Crawford Laboratories, Garland and Rustoleum. Urethane mortars combine cement with water based urethane technology to produce a mortar product exhibiting properties of both.
Continued development over the past 15 years has in these systems with increasing high resin content and low viscosity. Designed to exhibit a high cross-linked density, cementitious urethane systems are non-toxic, non-hazardous, and highly chemical resistant and further developments allow for more effective and efficient installation.
Because of low temperatures during installation urethane mortar flooring is ideal for food processing and pharmaceutical manufacturing facilities. Floors in these environments are subjected to abuse, heavy traffic, chemical attack, extreme temperatures resulting in extremely hostile conditions. Urethane mortars do well in these abusive environments but may not be required in every plant area. Epoxy mortar systems, due mostly in part due to cost, are still the preferred material for less demanding environments.
The advantages of applying a urethane mortar flooring system are numerous. The cementitious urethane composition has a similar modulus of elasticity to that of concrete. This all but eliminates differential flexing that is prevalent with most other resins.
In addition to being able to absorb and withstand extreme heat and cold temperature change, urethane mortar systems also have sound deadening properties. These are particularly useful in areas exposed to steel wheel traffic such as bakeries. Urethane mortars can also effectively withstand abuse from impact such as dropping of objects such as pots and pans found in commercial kitchens.
Another advantage of urethane mortars is that typically do not require a primers saving considerable installation time. Primers for urethane mortars do allow for installation over dairy brick and tile eliminating the need for removal of existing flooring while eliminating the need for regular maintenance of grout joints. In the case of new concrete the unique chemical composition of urethane mortars with their similarities to concrete allow for installation over freshly poured concrete, thus eliminating the need for the typical 28-day wait time for the concrete to cure.
While there are numerous advantages to urethane mortar flooring systems, there are several disadvantages too. Having a cement and water cure, installation of these systems should be avoided at temperatures over 90 degrees F to reduce the risk of blistering from increased carbon dioxide being trapped during the rapid initial curing process. Due to their rapid cure time the installation of a urethane mortar system their primary purpose is for performance where as epoxy floor systems tend to allow for more decorative installations.
Urethane mortars are available in three primary forms a trowel applied mortar, a self-leveling slurry and a self-leveling slurry that can also be broadcast into for an aggressive anti-slip texture and/or a decorative quartz or ceramic carpet finish. All of thise installations typically range in thickness from ¼ inch to 3/8 inch with some newer products that can be applied as thin as 1/8 of an inch.
Polyurea is a subset of Polyurethane when isocyanates react with water to form a urea linkage and carbon dioxide gas; they also react with polyetheramines to form polyureas.
Polyurea applications include joint sealant technology. coatings and linings are most commonly seen applied over truck bed liners for corrosion protection and abrasion resistance. They also have tremendous advantages over conventional materials for joint fill and caulk applications due to their fast set nature, high elongation typically in excess of 300% and durability/abrasion characteristics. Polyurea comes in three primary formulations spray, caulk grade (packaged in dual component cartridges with special mix tips, and hand mix formulations.
Due to polyureas extremely fast cure nature (usually in less than a few seconds) specialized application equipment is often needed for installation. Polyureas are generally odorless with 0 VOC’s, extremely flexible and when sprayed due to lack of solvents allow for almost unlimited thickness in a single application.
Polyaspartic is a type of polyurea (actually a polyaspartic aliphatic polyurea). All polyureas are two-part systems, meaning that a resin has to be mixed with a catalyst to create the curing reaction that hardens the material. Polyurea has been used very successfully for corrosion-resistant coatings and repair materials, although application is awkward since it has an extremely short pot life—about 3 seconds, so the two parts must be mixed at the spray tip, requiring lots of maintenance on expensive high-pressure equipment.
Polyaspartic polyurea (or simply polyaspartics) overcomes many of those difficulties, while retaining the advantages by combining the best properties of polyurea and Aliphatic Urethane technology. According to Bayer Material Science, polyaspartics are "based on the reaction of an aliphatic polyisocyanate and a polyaspartic ester, which is an aliphatic diamine."
For most of us, the important thing to understand is that polyaspartics are a polymer coating material that has a rapid cure time for 5 to 120 minutes depending on formulation, can be applied to surfaces with extreme temperatures from -30°F to 140°F. Polyaspartics generally have very low viscosity, equivalent to water, which gives it outstanding wetting ability to apply a high build in one coat, UV stability, and excellent chemical and abrasion resistance thus providing some of the best properties of epoxy resins and urethane resin technology.
The main drawback, cost. Polyaspartic resins tend to be 3 to 10 times more expensive than 100% solids epoxy resins.
Polyesters are two-component systems in which a pre-polymer resin dissolved in styrene is mixed with a peroxide catalyst. Polyesters are fast setting, high strength, and demonstrate excellent resistance to acids and most solvents, but they are generally susceptible to alkali attack. Polyester resins experience a relatively high amount of shrinkage. Styrene flammability and fumes must be considered when using this product. Polyesters resins are most commonly used for chemical containment both primary and secondary in areas exposed to aggressive acids.
Vinyl Esters are a type or subset of polyester resin, in which the pre-polymers are formed by reaction of epoxy resin with acrylic of methacrylic acid. Vinyl ester resins provide ultimate performance in chemical / corrosion resistance. The products are typically formulated in high build, fast curing systems for corrosion resistance and toughness. Again, styrene flammability and fumes must be considered.
Oil Primers are designed specifically for old concrete that has been consistently exposed to oil. It is still a good idea to remove any surface oil as it can become acidic and wear away at the concrete however they can incorporate oil into their binding matrix and provide good adhesion to an otherwise un-adhere able surface.
Moisture Tolerant Primers
Moisture tolerant primers these products many of which are water-based epoxies provide a primer that can adhere to wet or damp concrete. Some moisture tolerant primers allow for application to “green concrete” or concrete less than 28 days old as well as creating a breathable surface where water vapor can travel up through it but still creates a waterproof surface.
Pre-Primers / Tack Coats
Pre-Primers are generally high solvent products that both clean and prime difficult to adhere to surfaces such as ceramic tile, quarry tile, dairy brick, and even glass allowing for the application of various resin systems as topcoats.