Real scale frost experiments on masonry wall elements, taken from the St. Gaugericus church at Roosdaal, are presented. The masonry shows severe frost damage. Damage sustained by the building were reproduced in laboratory experiment. Frost degradation of the masonry was attributed to the interaction of pointing mortar and bricks. The pointing mortar was replaced by four softer and less thermally conductive mortar systems. They were compared by their behavior in frost-thaw experiments on 1 m² wall elements. The best results were obtained with a pointing mortar system with hydraulic lime binder. -- AATA