Material having high mechanical strength and density close to unity, the manufacture and uses thereof

A material with high mechanical strength and a density of about 0.70 to 1.15 g/cm.sup.3, characterized in that it is obtained by a process which consists essentially of:

• a step (a), in which a composition consisting essentially of melamine-formaldehyde resin, hollow microspheres having an apparent density of about 200 to 450 kg/m.sup.3 and being other than clay or schist and light aggregates having an apparent density of about 0.75 to 1.1 g/cm.sup.3 and being selected from the group consisting of expanded clay and expanded schist is dispersed in water, the proportions of the constituents used range from 10 to 50% by weight, for the melamine-formaldehyde resin, from 10 to 50% by weight for the hollow microspheres and less than 60% by weight for the light aggregates,
• a step (b), in which the dispersion thus formed is mixed, in the presence of a cross-linking catalyst for the melamine-formaldehyde resin, until a fluid paste is obtained;
• a step (c), in which said fluid paste is allowed to harden at a temperature from 5.degree. C. to 60.degree. C. into the desired material.