Vertechs recommends Thermocrete for any chimney lining applications.

THERMOCRETE is a revolutionary process which allows your existing chimney to be lined without any construction work.

The material used for this is THERMOCRETE B2C a lightweight, but incredibly strong Monolithic Refractory Castable, reinforced with Ceramic Fibres. It will restore your chimney-stack to perfect condition (making it stronger than new), ensuring the flue is correctly sized for the appliance, increasing the flues efficiency, completely curing the existing damage and preventing further deterioration.
THERMOCRETE is impervious to combustion gasses and acid attack,: it also has excellent insulation properties.