castor oil polyether based polyol a tin catalyst and a thickening agent along with a polymeric isocyanate activator and a polyurethane or polyurea aromatic or aliphatic coating atop the substrate base in providing a very tough but flexibly soft non cracking overlay which moves with the floor application_number US 27045402 A description the flexible flooring system of the invention includes three layers first an epoxy or polyurethane primer of any available composition is installed on the concrete or other floor second a two component ambient temperature cured polyurethane membrane substrate base is applied atop the primer by one of a pumping or pouring process third a polyurea or polyurethane aromatic or aliphatic top coat is applied atop the substrate base in accordance with the invention such substrate base is comprised of two separate components a resin side polyol blend and a polymeric isocyanate activator the polyol blend is composed of a polyether based polyol a urethane grade castor oil a tin catalyst a moisture scavenger and a thickening agent the mixture can be carried out in a large mixing vessel at room temperature the liquid mixture part of the polyol blend contains a urethane grade castor oil to an extent of 60 70 by weight u2014 for example 65 a castor oil of a very low moisture content is preferable to eliminate activation with the polyether based polyol this polyol is then mixed with the castor oil in a proportion of 30 by weight polypropylene oxide is particularly useful as the polyether based polyol a tin catalyst is then.