Method of forming refractory masses from compositions of matter of specified granulometry

A process of forming a substantially crack-free refractory mass on a surface, which process comprises spraying against the surface a mixture of refractory particles and oxidisable particles which react exothermically with oxygen to generate sufficient heat to soften or melt at least the surfaces of the refractory particles and so bring about formation of the refractory mass, and causing the sprayed mixture to be heated sufficiently to cause the oxidisable particles to undergo such exothermic reaction, characterised in that the granulometry of the particles which are sprayed in the mixture is such that the mixture has refractory and oxidizable particles of 80% grain size and of 20% grain size, the mean of the 80% and 20% grain sizes of the refractory particles is greater that the mean of the 80% and 20% grain sizes of the oxidisable particles and that the size range spread factor of the refractory particles is at least 1.2, the size range spread factor of the refractory particles being equal to:

• ##EQU2## where G.sub.80 is the 80% grain size of the refractory particles, and G.sub.20 is the 20% grain size of the refractory particles.