Abstract: The invention provides a method of building or repairing refractory brickwork structures that are subjected to local differences in thermal expansion. The brickwork joints are made with a suitable sintering refractory mortar and in most or all of the joints there is also provided a synthetic material layer that changes into gaseous products when heated, without leaving any substantial solid residue and without reacting chemically with the refractory structure. The volume of the layers is not more than 95% of the thermal expansion of the brickwork adjacent the joints during heating up to working temperatures, so that the joints are left in compression to ensure gas tightness.