Abstract: The invention relates to mortars made of clay, cement, water and an urea-formaldehyde or melamine-formaldehyde resin.Paraffin is added to the powdered cement and, just before shaping the mortar, there is added to said mortar sodium aluminate and sodium silicate.

Abstract: The invention provides a clay/cement mortar which sets without cracking to a product having good mechanical properties, the mortar containing cement, clay in an amount by weight greater than that of the cement, gauging water, and an additive chosen from urea-formaldehyde and melamine-formaldehyde resins and derivatives of ammonia such as formamide, the dry weight of additive being between 1 and 20% of the total dry weight of the clay and cement. The clay is preferably basic or rendered so by addition of silicates or sodium aluminates, and absorbed water is preferably removed therefrom before mixing with the cement by adding a flocculant or water repellent. Adjuvants which may be incorporated in the mortar include paraffin, aluminium powder, glass and the like, and acrylic, A.B.S. and the like polymer emulsions. The mortar, after being formed to desired shape, is preferably kept for several hours in an atmosphere saturated with water vapor before being dried slowly to cause setting with curing of the additive.