When forming a refractory mass on a surface a mixture of oxidizable particles and refractory particles in a comburent carrier gas is sprayed against that surface from an outlet of a lance. Thus on combustion of the oxidizable particles, sufficient heat is generated to soften or melt at least the surfaces of the refractory particles to bring about the formation of the refractory mass. The mixture of particles is itself mixed with a carrier gas stream, for example, by using venturi, and is fed along a line towards a lance outlet. Oxygen is introduced into such feed line at at least one location along the feed line and is mixed with the carrier gas/particle mixture during its flow towards the lance outlet before reaching that outlet, and preferably at least one meter from the outlet of the lance. The addition of oxygen may take place via a connector. |