Surface treatment of refractories

A ceramic welding process in which a coherent refractory mass is formed adherent to a refractory structure at a weld site by projecting a powder stream carrying a mixture of particles which comprises fuel particles and refractory oxide particles against the weld site and the fuel particles are caused or allowed to burn to soften or melt at least the surfaces of the refractory oxide particles so that a coherent refractory mass is formed adherent to the structure, wherein, in a preliminary treatment step, the weld site is cleaned by a process for cleaning a surface of the refractory structure which is at an elevated temperature and which surface includes the weld site, comprising:

• projecting against the surface a comburent gas stream which is a powder stream comprised of fuel particles carried in an oxygen-containing carrier gas, the comburent gas stream impinging upon the surface at an impingement zone, whereby the fuel particles are caused or allowed to burn in a reaction zone defined generally around the impingement zone at the surface and heat generated by the combustion of the fuel particles causes the surface or material adhered thereto to melt thus providing a melted material, and
• projecting a separate scouring stream comprising oxygen simultaneously or alternately at the surface to scour the surface in a vicinity of the reaction zone thereby cleaning the surface due to the scouring stream blowing away the melted material.