The invention relates to a powder comprising more than 70% of glass-ceramic and/or refractory particles, a particle of said powder being classed in the fraction called "matrix" or in the fraction called "aggregate" according to whether it is smaller than, or equal to 100 μm, or bigger than 100 μm, respectively, the aggregate, representing more than 60% of the powder, comprising: more than 40% of particles of a glass-ceramic material having a crystallisation rate of higher than 50% and a thermal expansion value, measured at 700°C, of less than 0.3%, called "glass-ceramic grains"; less than 35% of particles of a refractory material different from a glass-ceramic material, called "refractory grains", the quantity of refractory grains being higher than 10% if the aggregate comprises more than 40% of glass-ceramic grains having a thermal expansion value, measured at 700°C, of less than or equal to 0.15%; the matrix, representing more than 10% of the powder, comprising: less than 30% of particles of a refractory material different from a glass-ceramic material,called "fine refractory particles", the quantity of fine refractory particles being higher than 5%, and preferably lower than 25%, if the quantity of glass-ceramic grains having a crystallisation rate of lower than 75% is higher than 5%; and between 0.1% and 18% of particles of a heat-activatable binder; all of the percentages being weight percentages in relation to the weight of the powder.