The right flooring system means more uptime

Jan. 3, 2007
Functional testing is the key to getting it right the first time.

A polyurethane mortar overlay system, while not perfect for every plant, has advantages over other flooring systems in many applications. When it comes to manufacturing operations, floors get no respect.

They suffer a daily dose of foot and vehicle traffic, impacts, abrasion, thermal cycling, cracking concrete and aggressive clean-up procedures. In some facilities, the variety of spilled chemicals makes the table of contents for an encyclopedia look short and simple.

Whether interior or exterior, manufacturing exposes flooring surfaces to moisture vapor transmission, ultra violet light, and a wide range of temperatures, possibly including freeze thaw cycling.  While floors may be under constant attack, most facilities restrict allowable repair time. Downtime costs can exceed the cost of the materials and labor for the floor. If a flooring system fails to survive conditions in your plant, it must be removed and a new floor installed. More costs, more downtime.

Concrete is a well regarded and inexpensive building material. It has impressive compressive strength, but serious shortcomings as a flooring surface. These include dusting, cracking, spalling and low resistance to chemicals and wear. Concrete also stains easily and is generally considered to be unsightly.

One solution is to protect concrete with a fluid applied resin flooring system. These toppings form jointless monolithic surfaces that stop chemical penetration, eliminate dusting and, to varying degrees, protect against other forces that damage concrete. The basic resin families are epoxies, polyurethanes, polyesters, vinylesters and polyurethane mortar overlays.

Most flooring systems have an Achilles' heel. Some crack and chip. Some have marginal abrasion tolerance. Some delaminate under thermal cycling. Most resist some chemicals but deteriorate when exposed to others. Solvent based systems give off odors during installation. Multi layer systems like many epoxy overlays can require several days to install and cure fully.

Polyurethane mortar has few of these problems. It has the widest range of thermal and chemical resistance of any monolithic flooring system. It is excellent against abrasion, impact, and rapid temperature changes.

In the past thirty years, polyurethane mortar overlays have been installed around the world. The overlays show up in practically every type of manufacturing facility, from automaking to electronics manufacturing to paper processing to chemical processing to oil refineries. Aircraft hangers, kitchens, laboratories, breweries, warehousing and wet and dry food processing and storage facilities also used it.

There are millions of square feet of polyurethane mortar overlays installed in North America. It is a versatile product. In addition to floors, it sees service in containment trenches, berms, and coving as well as in re sloping floors.

But it is less well known than other systems like epoxies. One reason is that although it is readily available, polyurethane mortar overlay is patented worldwide and provided by just one manufacturer.


Impact resistance: Polyurethane mortar overlay absorbs impact by distributing it. This plastic property eliminates the chipping that more brittle flooring materials or layered systems experience.

Wear resistance: Not only does a polyurethane mortar overlay wear better than concrete, it may be better in this area than any other monolithic flooring system.

Temperature resistance: Polyurethane overlay retains its physical properties from  100 to 220 degrees Fahrenheit. As a single layer system, it withstands thermal shock. It stands up well to cleaning with steam, hot water, aggressive detergents, and disinfectants.

Chemical resistance: As mentioned earlier, polyurethane mortar overlays resist a wide range of chemicals, including acids, alkalis and solvents.  While other flooring systems may be more resistant to certain chemicals, this often comes with less abrasion and impact resistance or at a much higher cost.

For example, specially formulated epoxies are better against alkalis and Novolac vinylesters are better with solvents. Vinylesters can perform poorly under heavy vehicle traffic or other sources of physical wear.

In addition, manufacturer's guidelines for chemical resistance are only a starting point. Manufacturer's generally test their flooring systems against one chemical at a time. Most plants use a number of chemicals simultaneously, all of which inevitably end up on the floor.

When two or more chemicals mix, the combination could be bad for your floor. It is impractical for manufacturers to test each flooring system against every possible chemical combination. If you have any doubt about whether a certain system will work in your facility, install a test patch.

This touches on the basic difficulty in selecting a flooring system--balancing flooring strengths and weaknesses against chemicals and conditions in a manufacturing area. Any system that combines excellent abrasion, impact, and temperature resistance with resistance to a wide range of chemicals becomes a good choice for many applications.

Fast installation: The recommended concrete substrate preparations for any resin flooring systems is essentially the same. But once the concrete is ready, application times vary widely.

Any multi layer system, such as many epoxies, take several days to install. Then they require five to seven days of curing to reach optimum chemical resistance. On the other hand, polyurethane mortar overlays, polyesters and vinylesters cure rapidly. A repaired area can be returned to full service within 12 hours.

Multi layer polyurethane overlay can be installed in about half the time. Multi layer installations are more decorative and provide additional slip resistance when warranted.

When installing a floor over newly poured concrete, most systems require waiting either 28 days or until the moisture content falls below four percent. While not normally recommended, a polyurethane mortar overlay can be applied after the seven to 10 days it takes the moisture content to drop below 10%.

Like any good floor, once installed, polyurethane mortar overlays stay put. It strongly resists disbonding because its bond strength exceeds the tensile strength of concrete. The water borne polyurethane overlays are essentially odorless. While vinylesters and polyesters cure rapidly, they give off styrene during curing. Styrene has low toxicity, but the smell is obnoxious.

Some flooring systems are solvent-based. These systems can offer improved properties at a lower cost. But with increasing fire and health regulations, solvent products find use in fewer and fewer applications. When they are used, the installation team must restrict access and take additional safety precautions.

Clean living: Bacteria feeds on some flooring systems. These systems cannot be used in food processing and related operations. Polyurethane mortar is USDA accepted, a designation based on rigorous standards. It does not foster bacterial growth and it withstands aggressive cleaning with steam, hot water, tough detergents, and disinfectants. Accordingly, many dairies, bakeries, kitchens, meat, poultry and food processing facilities use it.

Installation: Most flooring systems are best installed by manufacturer approved contractors. Polyurethane mortar overlay is no exception. The components—a mineral aggregate, polyurethane resin, a catalyst, and a powdered composite that includes—requires mechanical mixing on site.

The overlay can be installed on new or existing concrete floors, even badly damaged ones. There are two versions: a trowel applied single layer system and a more decorative self leveling system. The latter uses a silica or quartz broadcast aggregate in single or multiple colors for slip resistance.

Preparing the concrete substrate is the key to any successful floor installation. This bears repeating. Many floor problems can be traced to inadequate preparation. Remove laitance from freshly poured floors by shotblasting or other methods. Chemically clean contaminated concrete with chemicals or other materials before mechanical cleaning it. Replace severely contaminated concrete so a flooring system will bond to it. Install the overlay at temperatures between 40 and 85 degrees Fahrenheit.

Repairs: Because it is a uniform flooring system with excellent bonding properties, it can be successfully patched and retain the monolithic integrity of the floor

Why isn't every floor a polyurethane mortar overlay?

For several good reasons. While the overlay is highly functional, it is difficult to consider the single layer version decorative. However, the multi layer system that accounts for about half the systems being installed is a substantial improvement.

Another reason is competition. One expert estimated that epoxy floors are available in thousands of versions, each with different properties. Manufacturers custom formulate epoxies and other flooring systems to excel in certain properties. The upside is the possibility of getting a floor that is well matched to your conditions. The downside is confusion.

Epoxies have another advantage. They generally have a lower installed unit cost. On the other hand, a polyurethane mortar overlay can last longer because it resists disbonding and is highly resistant to impact, abrasions, and many chemicals.

The good news is that the systems can be mixed and matched throughout a facility, even butted up to one another. Know your conditions then test. Manufacturer's guidelines are just that. Specify a flooring system by comparing the conditions where the floor will be installed  to the guidelines. Keep in mind that the single weakest property of a flooring system might undo its strengths.

For example, a system with good resistance to your mix of chemicals is no good if it disbonds from rapid temperature cycling or heavy forklift traffic.

As mentioned throughout this article, it pays to test your leading candidates in the environment where the new floor will be installed. The last thing you want is more manufacturing downtime from demolishing and removing to an unsuitable floor to install a new one. In a word,  test.


Its excellent physical properties make polyurethane mortar overlay floor systems superior at protecting concrete in many applications. It has excellent resistance to acids and to a wide range of chemicals. Given the infinite variety of conditions found in manufacturing operations, no single flooring system is right for every application. Specifying a seamless flooring system that will perform for many years is a matter of studying the conditions in your plant, working with manufacturers to develop a short list, and then testing those products to be sure they work.

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