Also commonly referred to as urethanes, polyurethane sealers or coatings are also thermosetting polymers like epoxies and are considered to be high-build concrete sealers which offer a very durable finish that is resistant to chemicals. This type of concrete sealer is almost two times thicker when compared to acrylic sealer. It forms a high-build film on the concrete surface and offers excellent protection against chemicals and abrasion.
Polyurethane sealers are available in two versions: water- and solvent-based sealers. They are also available in various shine levels and various finishes from gloss to matte. These concrete sealers can be used on both exterior and interior concrete, and provide a durable and non-yellowing finish.
Aliphatic polyurethane sealers are ideal for garage floors and although they contain around 60–70% solids, the polyurethane coating is around 2–3 mils thick only. In one application, polyurethane coatings cannot be applied thicker like some of the epoxy coatings.
Polyurethane coatings are more flexible compared to epoxies, making their surface more resistant to scratches. It also offers higher resistance to abrasions and can absorb impacts better. Polyurethanes also have a higher resistance to chemicals compared to epoxies and it is also UV stable, i.e., when exposed to sunlight, it will not turn yellow over time, unlike epoxies. They also tolerate humidity and larger swings in temperature much better than epoxies.
However, despite the several advantages that polyurethanes have over epoxies, the bonding with concrete is not very efficient and they do not work very well in filling cracks and divots on the concrete surface. Also, since most polyurethanes are solvent-based, they can have high VOC and there may be restrictions on the use of polyurethane coatings/sealers in many states and counties.
Polyurethane concrete sealers can be used for the following:
When applying polyurethane concrete sealers, you need to take extra care compared to other sealers like acrylic-based sealers. You must not apply the water-based polyurethane sealer with a garden pump sprayer because they do not provide the pressure required to get an even and thin spray. Instead, it is better to use a high-pressure, low-volume airless sprayer or you can apply the sealer using a microfiber mop, whose push-pull motion will allow you to get a thin and uniform coverage.
Most of the polyurethane concrete sealers are not tolerant of moisture and so, if there is any water present on the surface, you must avoid applying the sealer. The presence of water will cause bubbling and foaming and the sealer will also not allow the moisture to escape from the concrete surface, which can cause problems on exterior surfaces like driveways or sidewalks.