Abstract: The invention is directed to a process of forming a ditch liner by dispensing a solidifiable liquid mixture onto a continuously moving porous blanket, applying pressure against the mixture and the coated blanket to form a continuous matrix within the blanket, laying the resulting coated blanket into a ditch before the liquid mixture has fully cured, conforming the coated blanket to the shape of the ditch, and allowing the mixture to fully cure. The improvement resides in using a reaction mixture of a polyisocyanate, up to 60% by weight of a filler, a specified polyol mixture and, optionally, a catalyst. The polyol mixture requires three different propylene oxide adducts: i) a propylene oxide adduct of an alkanolamine, ii) a propylene oxide adduct of a low molecular weight organic compound having from 3 to 8 OH groups, and iii) a propylene oxide adduct of a low molecular weight diol.