Abstract: The disclosed process for making a high % solids, one-part, curable, essentially flowable or pumpable, high equivalent weight polyurethane (i.e., polyol-polyisocyanate adduct) prepolymer composition involves de-watering the polyol component of the reaction mixture with an alkaline earth metal oxide, preferably calcium oxide; adding the minimum acceptable level of catalyst for the NCO/polyol reaction; exothermically reacting a partially hindered aliphatic polyisocyanate such as isophorone diisocyanate (IPDI) and a partially hindered aromatic polyisocyanate such as 2,4-tolylene diisocyanate seriatim, so that at least about one-fourth of the IPDI reacts before the 2,4-TDI is added; and then adding more catalyst for the curing (e.g. moisture cure) reaction.