Choosing between epoxy, polyurethane and PU cement

Most specification errors in resin flooring are not errors of workmanship. They are errors of chemistry: a system chosen for the wrong set of conditions, installed correctly, and failing anyway. Epoxy, polyurethane and polyurethane cement are all resin systems, and they all produce a seamless floor, but they behave differently under heat, moisture, impact and chemical load. The choice between them follows from the building, not from preference.

Epoxy

Epoxy resins cure to a hard, dense, closely bonded film with high compressive strength and good adhesion to prepared concrete. They accept heavy pigment loads, level well, and can be built from a thin sealer of a few hundred microns to a self smoothing layer of several millimetres. Epoxy is the usual answer where the demand is mechanical: wheeled traffic, point loads, abrasion from pallet trucks, and a surface that must stay cleanable.

Its limits are equally clear. Cured epoxy is relatively rigid, so it tolerates movement in the substrate poorly and will crack where the concrete cracks. It is sensitive to temperature during cure, and most formulations discolour under ultraviolet light, which is cosmetic rather than structural. Resistance to concentrated organic acids and to sustained hot water is modest. In a room washed daily at high temperature, epoxy is rarely the right first choice.

Polyurethane

Polyurethane systems cure to a more elastic network. That elasticity buys two things: better distribution of impact energy, and a greater ability to bridge fine movement in the substrate. Where a floor sits over a slab with hairline cracking, or where heavy items are dropped, a polyurethane wear layer usually outlives a comparably thick epoxy one. Polyurethane also holds colour under daylight far better, which matters in showrooms, public buildings and glazed production halls.

Polyurethane is generally softer than epoxy at equal thickness, so it can mark under narrow static loads such as thin racking feet. It is also more sensitive to moisture and humidity during application, and the workable window is shorter. It is a coating and screed family rather than a single product, and behaviour varies widely between aliphatic and aromatic types.

PU cement

Polyurethane cement, sometimes written as PU concrete, combines a polyurethane binder with cement and graded aggregate. The result is a heavily filled, dense, mineral rich screed, normally laid between 4 and 9 mm, that expands and contracts at a rate close to that of the concrete below it. That single property is why it survives thermal shock: steam cleaning, hot process water, blast freezing, and the daily cycle between a cold store and a wash down bay.

PU cement also tolerates a damper substrate than epoxy, resists organic acids, fats, sugars and lactic acid well, and can be finished with a textured surface for slip resistance. The trade off is appearance. It is a working floor, matt and granular, with limited colour range and visible trowel character. In food production that is the correct floor. In a reception area it is not.

What to establish before deciding

• Surface temperature and the cleaning regime, including the temperature and frequency of any wash down or steam cleaning.
• Chemical exposure, named rather than described: which acids, fats, solvents or cleaning agents, at what concentration and contact time.
• Mechanical load: wheel type, axle load, point loads from racking, and any impact.
• Substrate condition, including residual moisture, existing cracking and whether a damp proof membrane is present.
• Appearance and light: colour retention, gloss level and daylight exposure.
• Downtime available, because cure schedules differ substantially between the three families.