The WAC for the same mortars AIM-100 between high WAC brick is shown in Fig. 7b. It is apparent that the brick substrate has greatly reduced the WAC for a given mortar and more so for the thinner mortars. Additionally, the silica sands generally yield a greater reduction than do the carbonate sands. For example the average reduction for all silica sands in 10 mm samples is 51% whilst that for the carbonate sands is 45% which may be related to the desorption of the mortar by the substrate. Mortars produced with the sands of lower fines content (S1, S2, C1 & C2) show a consistent WAC reduction trend as the sample thickness decreases, independent of their mineralogy. When finer sand is used a consistent WAC reduction with thickness is observed for only the S4 sand mortar cast in the brick mould (Fig. 7b). Unlike the influence of sand “mineralogy” on strength (see Section 3.2.1) there is a consistent influence on WAC. In 29 of the 32 mortar combinations measured the WAC of the carbonate sanded mortars was higher than their silica counterparts and no influence of grading, sample thickness or substrate was observed. The average of the ratio of WAC carbonate:silica sands was 1.41 for the brick substrate and 1.27 for the steel substrate although the difference is not statistically significant.