Architects specify epoxy, methyl methacrylate (MMA), and cementitious urethane to counteract concrete’s inherent porosity. Unlike penetrating sealers that scratch and scrape away, coatings lay on top of the surface to form a barrier against anything – foot traffic, liquids, salt, heavy equipment, etc. – that could damage it.
They’re not invulnerable, however; and that has implications for customer satisfaction if they’re improperly maintained.
A Brief Chemistry Lesson
In general, thicker coatings are more durable. Epoxies are thinnest and may become brittle with age, MMAs are slightly thicker, and urethanes are thickest. The basic ingredient of all three is resin, a material similar to plastic. Each responds differently to bacteria, chemicals, weight, and heat. Taking a one-size-fits-all approach to maintenance risks to floor failure caused by blistering, delamination, embrittlement, erosion, and softening.
Epoxies and cementitious urethane durability depends on the bond between two components. For epoxies, that’s epichlorohydrin as the epoxy element and amine that acts as a hardener; for cementitious urethanes, it’s polyol and aromatic isocyanate combined with Portland cement and sometimes strengthened with quartz and flint. Cleaning regimens shouldn’t stress the bond, referred to by chemists as a cross-linked matrix.
MMA is an acrylic: methacrylic ester combined with an organic peroxide, usually benzoyl peroxide (BPO). The peroxide acts as a catalyst that, instead of creating a matrix, fuses the material into a solid mass.
As resins, they’re all vulnerable to phenol (otherwise known as carbolic acid, which is high-alkaline), hydrocarbon-based solvents, and methylpyrrolidone.
What This Means in the Real World
Common in disinfectants, phenol is good at killing bugs and bacteria but weakens the interaction between two-component epoxies and cementitious urethanes. MMAs are less susceptible because the material’s not a matrix; but even they eventually discolor, soften, and lose mechanical strength.
Conversely, MMAs methacrylic ester is more affected by solvents compared to all the other chemicals that go into resin floors. This means that cleaning solutions with solvents will corrode and deteriorate the component that makes up the backbone of an MMA system.
The epichlorohydrin and amine components of epoxies react less with solvents, but cementitious urethane is most resistant. This stems from the fact that when a polyol and isocyanate form a high cross-linked density, it creates a system with a very high level of chemical resistance (with phenols being the exception to this rule). The better this cross-linking, the better the chemical resistance. An additional factor to the chemical resistance of cementitious urethanes is the ‘functionality’ of the isocyanate in the system. This effectively indicates its reactivity and the higher this is, the more chemically resistant the coating will be.
Stripping solutions often contain methylpyrrolidone, which is odorless. Customers use cleaning solutions assuming they’re benign because they don’t have a pungent smell and inadvertently wreck all three coating types.
Like polished concrete, resin-based coatings should be dry-mopped daily to remove scratch-causing grit and dust and never waxed. Also:
- Use pH-neutral cleaners. Give the solution time to loosen dirt and debris, but don’t let it dry.
- Rinse well to keep the solution from building up and over time creating a slippery surface.
- Immediately remove oil and grease with a water-based solution of alkaline detergent.
- Clean high-traffic locations like entrances and areas subject to accidental contamination by chemicals or bacteriological materials more often.
- Use brushes instead of mops on textured coatings (primarily cementitious urethanes, although some MMAs are also textured).
- Hot water and steam cleaning can crack, delaminate, and erode resins. Epoxies struggle with temperatures above 170 degrees F; cementitious urethane withstands temperatures to 250° F.
MMAs: A Class of Their Own
Acrylic is less sensitive than epoxies and urethanes to high pH values; therefore, all-alkaline cleaning agents, whether sodium or potassium hydroxide, are fine. (If an acidic cleaner is preferred, use one based on phosphoric acid.) Nor are surfactants and hypochlorite additives harmful.
The following are harmful:
- Organic solvents
- Aromatic or halogenated hydrocarbons
- Alcohol. Depending on concentration and exposure time, white discoloration and damage can occur
- High concentrations (30% or more) of ammonia or ammonium chloride, which cause yellow or brown discoloration (small-quantity solutions, 1%, for example, are OK)
- High concentrations (30% or more) of hydrogen peroxide over several hours, which causes irreversible red discoloration
- Permanent exposure to hot water causes white discoloration.
Suitable maintenance products and procedures:
- For disinfection, use cleaners with a hypochlorite, formaldehyde, or hydrogen superoxide base
- To remove lime specks, use a dilute hydrochloric acid or weak acetic solution (up to 10% if subsequently neutralized)
- A 0.7% nitric acid solution at 70°C may be used when cleaning steel components; however, exposure to high concentrations (around 54%, for example) causes yellow discoloration and ruins the coating even at room temperature
- Squeegee smooth surfaces; brush or scrub anti-slip finishes to remove grease and other debris from surface depressions.
- If the surface is too large for hand cleaning, a scrubbing machine with rotating brushes should be used alongside a water suction appliance to take up the water.
- An appliance that combines a scrubber and water suction with brushes at the front and that sucks up the dirty water at the back of the tank is advisable. A machine with roller jets is recommended. It’s important to be able to adjust height to match the floor’s roughness.
- If using high-pressure and steam cleaners, pressure shouldn’t exceed 50 bar and maximum water temperature is 50°C. For short durations up to 80 bar and 80°C can be used on certain places.
What Funny Colors Mean
Discoloration occurs when dye penetrates the resin; it can’t be removed by scrubbing or chemical intervention but doesn’t affect coating performance. Neither does pigment leaching, which occurs when a chemical reacts with pigment in the resin, permanently changing its color.
Discoloration and pigment leaching can, however, be early warning signs of chemical attack. Keep an eye on color changes, because they could indicate that the coating is deteriorating and could fail.
Coating Care Basics
|Solvent- or water-based epoxy||150 to 330 microns||2-3 years||Wet mop and clean with single-disc rotary scrubber (ride-on scrubber dryer for large areas), then damp mop and allow to dry; use water less than 170 degrees F|
|High-build epoxy||200 to 1,000 microns||3-5 years||Mechanical scrubber with very fine, fine, and medium-grade pads; rotary brush and vacuum machine for thicker floors; no steam cleaning or water hotter than 170 degrees F|
|Trowel-applied epoxy||4 to 6 millimeters||10 years||Scrubber drier: Steam cleaning depends on coating thickness and frequency; err on the side of caution|
|Methyl methacrylate (MMA)||3 to 7 millimeters||15+ years||Squeegee for small, smooth areas; hard scrubber for textured areas; scrubbing machine with rotating brushes for large areas|
|Cementitious urethane||4 to 9 millimeters||25+ years||High-pressure washer and cleaner/scrubber; steam cleaning and water up to 250 degrees F fine|