Polyurethane is the reaction product of a hydroxyl containing polyol (OH) and polyisocyanate (NCO), and the resultant polymer is an exceedingly cross-linked film having exceptional abrasion resistance, while the linear polyols in the PU chain render flexibility. Urethanes perform ablest when placed on dry concrete, but are not proposed for damp concrete as moisture inhibits the cure and can cause blistering because of its undesirable reaction with water, generating carbon dioxide gas. Polyurethanes, both aromatic (yellowing) and aliphatic (non-yellowing) are employed as thin coatings as well as self- levellings.