The instant invention relates to a one-step process for the production of elastomeric moldings which have a compact surface by the technique of reaction injection molding, using highly reactive systems of specific polyisocyanates, polyhydroxyl compounds and specific active aromatic polyamines. The instant invention further relates to active hydrogen containing blends useful in preparing elastomeric moldings, said blends comprising polyhydroxyl compounds, and specific active aromatic diamines. The blends herein may also contain catalyst for the reaction between hydroxyl groups and isocyanate groups.