Best practices for specifying resinous flooring systems

October 19, 2021

Photos courtesy Res-Tek Inc.

By Joe Lasko

There are some flooring chemistries that have existed in the United States for more than 15 years but are rarely specified relative to their epoxy counterparts. Epoxy has become the Kleenex or Band-Aid of resinous flooring. That said, every construction project has certain needs that cannot always be solved by only specifying one flooring type or chemistry.

So, what other resinous flooring options are available? Urethane cements, methyl-methacrylate (MMA), urethanes, and polyaspartics have already been established as viable resinous flooring solutions for a variety of challenges. Urethane cements, for example, are good for resisting thermal shock from steam, grease, and other hot contaminants, while MMA can accept a fresh topcoat at any future time without requiring mechanical preparation.

The best practice for a specifier is to partner with a manufacturer. When partnering with a resinous flooring manufacturer, there are endless combinations of system builds that can be customized to achieve the perfect system for the customer. Epoxy still belongs in certain specifications, but urethane cements, MMAs, and polyaspartics all deserve equal consideration based on the project’s demands.

Therefore, it is important for one to understand not only the basics on what resinous flooring is, but also the different chemistries and why they each deserve consideration in specifications.

What is resinous flooring?

Resinous flooring, also known as fluid-applied or poured-in-place flooring, is common in industrial and commercial environments.

Its properties allow for a smooth, non-porous, easily cleanable surface that cannot be achieved with any materials that have grout or seams.

Resins can be a natural or synthetic liquid substance and sometimes have a yellowish or brown color. Resinous flooring comprises specific resin formulas applied in several layers that bond together either adhesively or chemically. Once ‘cured’ the layers form a hard surface which has various performance properties such as ultraviolet (UV) stability, abrasion resistance, or chemical resistance, among others.

It is important to take all environmental factors and design choices into consideration before choosing a particular type of flooring as resinous flooring is not a one size fits all product. The following are some specific considerations that should always be included in a resinous flooring design and specification.

Cove base should be specified at 102 or 152 mm (4 or 6 in.). Zinc strips can be used to provide proper height and a smooth transition to the wall.

Surface preparation

The most important foundation of a resinous flooring system is the substrate it is being placed on. The most common substrate is a concrete slab that is steel troweled or has a ‘darby’ finish. The top or ‘cap’ of the concrete substrate is the weakest part of the slab. Even if the resinous system can penetrate through the top of the slab, the ‘cap’ still may delaminate from the rest of the slab which would still result in a failure. This is one reason concrete can spall.

To prevent this from being a weak foundation of the flooring system, a concrete surface profile (CSP) must be specified. That specification is on a one to 10 scale with the latter being the most aggressive profile for products that will be laid thicker than a 6.4 mm (0.25 in.). This is important to specify correctly based on the system because the CSP may show through a thinner system, and the substrate may need to be patched to not telegraph through. On the other hand, if a substrate is not prepared well enough, the product applied may delaminate and fail.

How the CSP is achieved is up to the installer as they are liable for the installation portion of a warrantied project. Depending on the specified profile, project size, and specified system, an installer can choose a range of mechanical surface preparation techniques. Even though there are different methods, the entire substrate must be mechanically prepared to the specified profile. Commonly used equipment includes grinders, shot blasters, scarifiers, scrabelers, hammers, and sometimes even needle guns.

Moisture mitigation

The best way to avoid needing to specify a moisture mitigation component is to specify a vapor barrier (a.k.a. vapor retarder) under the concrete slab. A concrete slab on grade acts like a sponge and will absorb moisture from the soil or ground. In some cases, when this moisture is left unchecked, it can force the resinous system off the substrate causing a failure by delamination.

When writing a specification, it is important to include what the highest amount of moisture a resinous flooring or coating system can take before delamination occurs. This way testing can be performed and, if the result is higher than the upper limit of the product, a mitigation solution from the manufacturer can be used prior to the specified system to prevent the rest of the floor or coating from lifting off of the substrate.

The two most common testing methods are calcium chloride and relative humidity (RH) probe/meter. Both provide numbers correlating to the amount of moisture coming through the slab allowing a recommendation to be made to curb the moisture and still allow a successful flooring or coating installation. ASTM International standards for the two testing methods are ASTM F1869 as well as ASTM F2170.

Keying the substrate: Removal of concrete creates a void that is the correct thickness to accept the resinous system.

Cove base

One of the most popular reasons for specifying a resinous flooring system is because they are impermeable to water. So, a resinous system can act as both a user-friendly flooring system and as a waterproofing system. An important aspect of creating a floor that has a ‘bathtub effect’ is to specify a cove/wall base.

Typically, projects will only need a 102 or 152 mm (4 or 6 in.) cove base. Most projects will need 102 mm, while commercial kitchens and other wet areas will require 152 mm. Depending on the finish and the chemistry of the system, one may be able to specify that a product goes even higher up the wall.

Transitions and terminations

One important detail often overlooked in a specification is knowing what terminations and transitions to call out. This varies based on what type of flooring the resinous flooring is finishing up against. For example, if meeting up with a polished concrete finish, the resinous system will need to finish at ‘zero’ or flush with the concrete substrate that is going to be polished.

The most important consideration regarding transitions and terminations is the resinous system cannot be placed thin at these locations. If the thickness is not correct or matching the rest of the system, the terminations will be a weak point in the flooring system and will be the first points of failure either by delamination or chipping. After this has occurred, it can spread to the rest of the system leading to further failure. The correct way to install these terminations is to ‘key’ them in. ‘Keying’ the substrate means to remove a certain amount of concrete to create a void that is the correct thickness to accept the resinous system as it is poured in place.

With the best practices established for all resinous flooring, it is important to also look at the pros and cons of the most common resinous flooring chemistries.

1. Epoxy

Substrates must be mechanically prepared to the specified Concrete Surface Profile (CSP) based on the thickness of the flooring system.

Probably the most well-known chemistry in resinous flooring, epoxy is one specific class of polymers that contain epoxide groups, hence their name. There is an extremely large range of quality in epoxies. Flooring and coatings typically fall in the middle of that range. While these are not the same high-end formulations NASA uses, the space agency sources the same base chemistry as flooring, paint, and adhesive manufacturers.

The number of system designs using epoxy is endless and covers a wide spectrum of styles—from thin mil all the way to troweled down mortar systems. A few pros for using an epoxy system are its relatively reasonable material cost, epoxy systems usually have an attractive high-gloss finish and, depending on the formulation, can have zero VOCs in their make up.

Some cons to using epoxies are not all are formulated or produced with the same quality. For example, there is a difference in residential-grade versus industrial-grade epoxy. Typically, they all have a long cure time (eight to 12 hours) which only amounts to about 95 percent cured. Reaching 100 percent cured usually takes between seven and 10 days. Epoxy is also not UV stable, which means it will eventually yellow and color shift when exposed to UV light. This is especially important when using these flooring systems in an area exposed to sunlight or fluorescent light for extended periods such as grow houses or exterior applications. Although a system may use epoxy, it is rare one will find a manufacturer that will recommend finishing with an epoxy topcoat versus applying a urethane or polyaspartic topcoat due to them having better physical characteristics.

Further, because of the wide variety of epoxy system designs and qualities available, it is important that a specification be very specific. This can include the manufacturer’s system name or, at a minimum, type of resin, the application method, finish selection for texture and color, and an overall system thickness.

2. Methyl-methacrylate (MMA)

Examples of both good and bad drain terminations shows chipping and delamination at the drain.

Next, is a lesser-known chemistry, MMA. This organic compound is most commonly used in acrylic plastics like plexiglass or airplane windows. Pharmaceutical grade MMA is even used as a cement or glue in joint replacements, like a hip.

Known for its durability, MMA makes a great base chemistry for flooring and coating systems. The two largest pros for MMA are its ability to cure 100 percent in one hour and down to -26 C (-15 F) or up to 38 C (100 F) as MMA is not temperature dependent. It is also known for being UV stable which means it can be installed outdoors and will not yellow over time.

The two main cons of MMA are it has a relatively higher material price compared to epoxy. The second is it does give off an odor during installation. It has been described as a sharp, fruity aroma or one that is like a nail salon. Odors need to be managed and considered during any MMA project but is not usually a problem when proper ventilation methods are implemented.

Typically, the advantages of MMA chemistries listed above and its ability to accommodate recoating without mechanical preparation years later, can offset the higher costs of installation and stronger odors. One thing to keep in mind is no resinous system is odorless. Some systems just have less odor than others. MMA contractors are typically highly skilled installers and receive special training to be able to mitigate the odors with airflow. They also have crews prepared to work with a shorter pot life that still allows for an excellent installation curing in one hour.

3. Urethanes

This methyl-methacrylate (MMA) colored flake flooring in a supermarket is more than 12 years old and still looks new.

Urethane coatings are typically applied at a thin millage and as a final topcoat or seal coat to other flooring systems. Urethanes are most commonly created by reacting isocyanates with polyols. Other than floor coatings, urethane chemistry can be used in direct metal paint, truck bed or tank linings, and generic waterproofing.

Urethanes for flooring topcoats are known for their high abrasion resistance, chemical resistance, and UV stability. Most urethanes see their best usage in large, high traffic areas or over top of an epoxy or hybrid system. The downside to urethanes is their sensitivity to moisture and temperature fluctuation. It must be installed within a certain temperature range. Also, like epoxies, urethanes have a longer curing time—varying between eight and 24 hours—which varies by manufacturer as well.

4. Polyaspartics

Urethane in containment area.

Polyaspartics, which are like polyurethanes, are relatively new to the coatings market compared to other systems with their updated chemistry. Other than for resinous flooring, they are used in spray applied tank linings.

Manufacturers vary in opinion on typical uses for polyaspartics as a flooring material. They can be moisture sensitive when applied directly to a substrate. Most are used as broadcast coats or topcoats/finish coats in hybrid systems. Polyaspartics are great topcoats due to their fast cure times and the fact they are UV stable. They also cure very hard which means they may not accept recoats later without aggressive mechanical preparation; this can vary slightly by manufacturer as well. While the chemistry is the other fast curing product—one to four hours—its pound-to-pound price is higher than MMA and epoxies.

5. Urethane Cement

Urethane cement, also known as cementitious urethane, is exactly as it sounds—a urethane that is modified with cement. This chemistry has become a mainstay in resinous flooring due to its toughness. Two of its main strengths are its ability to withstand thermal shock of up to 115.5 C (240 F) and that it can be moisture resistant up to 9 kg (20 lbs) by calcium chloride test or 99 percent RH by RH in-situ probe testing.

Some negatives to urethane cements are slower cure times—eight to 12 hours between coats—and the install temperature needs to be maintained between 15.5 to 26.6 C (60 to 80 F) give or take. Still, the pros of being extremely durable and one of the toughest chemistries on the market will typically outweigh the cons depending on the project scope.

Urethane cement used in food processing area.

A word about topcoats

Different performance objectives can be achieved by choosing an appropriate topcoat, since this is the flooring system’s first line of defense. It is becoming rarer to find an epoxy product as a topcoat as the other chemistries perform better.

In hybrid flooring systems, often found in commercial kitchens, urethane cement is used as the body but different topcoats like MMA, polyaspartics, or urethanes can still give the customer the performance they need while providing different options for the finishes they are trying to achieve in their facility.

After the spec

The specification has now been published, what else can be done to ensure the customer’s needs will be met and that one’s design is honored as intended? Making sure a qualified applicator is setup to install the specified system is a great first step. An installer should be able to provide references to previously installed projects that are similar in size or scope, as well as be able to provide a letter or certificate that they have been trained and are authorized in the specified manufacturers’ system. These are two steps in submittals that can help protect a project’s integrity and warranties.

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