Bring the joints and wet cold seams with the help of a grinder, clean it from dust, fill in a waterproof rapidly accurate cement-sand mortar, and then grind the grout with a half-terrible. After several days, when the solution hardens so much that its surface humidity will be less than 15%, you need to smear with a roller or brush with a sealant and seams filled with solution. If the material has a high viscosity, dilute it with a solvent. In the process, the possibility of overheating of the repair cement-sand mortar should be excluded.
