Abstract: A process for reducing the cracking tendency and improving the strength of specified rammed plastic refractory reactor liners is described, the process comprising heating reactor liner mounted in a reactor, prior to its first use, to a temperature of from about 490.degree. C. to about 510.degree. C., the heating being carried out by heating said liner at a rate to produce a temperature increase of the liner not greater than about 6.degree. C. per hour. A reactor comprising a vessel or tube having a liner of the type specified and cured in the manner described is also disclosed.