The effect of adding up to 40% by weight of kaolinite and metakaolinite to cement-quartz mortars hydrothermally cured (autoclaved) at 175 degrees C was investigated by DTA. Tt is evident that aluminium substitution in the CSH-I lattice takes place with the clay additions in a manner similar to that observed for gibbsite addition, as reported in the previous paper (Part 1, Thermochim. Acta, 224 (1993) 241). Comparison between kaolinite and metakaolinite additions shows kaolinite to be the less reactive phase in these autoclaved cement-quartz mortars.