PURPOSE: To solidify a harmful aldehyde spill to reduce its odor by allowing a compsn. containing urea and acid and having specified pH to react with the aldehyde spill, and to easily clean the spill.

CONSTITUTION: A compsn. of pH 2 containing urea and acid is allowed to react with an aldehyde spill to solidify the spill and to reduce the vapor so that the spill is easily cleaned. The compsn. containing urea contains 50 to 65 wt.% urea and 5 to 10% acid (e.g. citric acid, fumaric acid) if the compsn. is solid. Or, the compsn. further contains 10 to 30% CaCl2. If the compsn. is liquid, it contains 30 to 100% urea and 5 to 10% acid (e.g. phosphoric acid and sulfuric acid). In a practical use, the urea compsn. is housed in a corrosion- resistant container and pressurized, and the compsn. is applied under pressure on an aldehyde spill so as to stir the spill and to produce a polymerized product in a short time to solidify. The polymerized material is a solid with little vapor and can be easily discarded.