A process is described for the production of joint foam characterized by the fact that gypsum dihydrate is suspended in water, the water slurry containing diphenylmethane 4,4' diisocyanate prepolymers, diphenylmethane 4,2' diisocyanate prepolymers, 2,4 toluene diisocyanate, 2,6 toluene diisocyanate or a mixture of these compounds is applied to the joint by intimate mixing and is allowed to cure.