A powdery composition based on silica for ceramic welding, in particular by projection, comprising from 10 to 90% of a phase of siliceous particles comprise at least 80% by weight of cristobalite and at most 15% by weight of tridymite, based on the total weight of the composition, from 90 to 10% by weight of conventional additives forming a binding phase, based on the total weight of the composition, said siliceous particles having a d50 comprised between 350 and 800 μm, preferably between 400 and 500 μm.