Both the polymers are versatile products and used extensively in industries like paints, sealants, adhesives, foams and resins. Both are very similar in polymer composition, however understanding its application for different situations is key to yield the best results for any material’s life.
Colour & Texture – In paint and resin industry, both the products are extensivley used and they possess distinct qualities in view of protection of paint. Epoxy is not resistant to UV light, thereby resulting in yellowing of colour over a period of time. It also becomes chalky and brittle at touch when exposed to UV for longer periods. On the other hand, Urethane is resistant to ultra violet light, thus maintaining the longevity of the paint finish and remains smooth throughout its life.
Chemical Resistance – Here Epoxy is highly resistant to acids and bases, thus providing strong protection against corrosion, whereas Urethane wears off and start corroding over prolonged exposure to harmful atmospheric gases.
Therefore for metal (particularly mild steel) painting, epoxy is always recommended to be used as base primer and finised with urethane coating especially when it is done in outdoors. Epoxy base coating may not be necessary with aluminium, stainless steel or titanium. Also, urethane provides the sheen and glossy texture to the metals.
Concrete Repairs – The general rule for this is that if concrete needs to be structurally repaired with very good compressive strength material then the choice is an Epoxy. Epoxy comes in different viscosities from ultra thin to paste like to accommodate the cracks of different widths. Colour pigments can also be added to match the existing colour.
If the crack in concrete only needs to be repaired for water leakage , polyurethane is an ideal choice. It is an elastomeric, fast setting foam that is effective alternative to seal the crack for any leakage only and not structurally. Since it is an elastomeric, it doesnt crack due to concrete’s movement owing to weathering.
Floor Coating – In floor coatings the principle is same as metal paints i.e. recommendation of using epoxy as base coating for better adhesion with concrete as per required build up owing to availibility of ranging viscosity, and then top coating with polyurethane as sealer layer for better resistance to wearing and abrasion. Sometimes, epoxy coating is also used as finished top coating depending upon particluar use and desired outcomes.