Two concrete classes with water to cement ratios of 0.38 & 0.50 were studied for moisture related indicators. These were relative humidity levels (internal, i.e. RBK method, and external) and salt deliquescence on concrete with unidirectional drying. A secondary cementitious material (SCM), ground granulated blast furnace slag, was used to replace 25 % of the reference cement (CEM I 52,5 R) at both w/c levels. Its effect on the above-mentioned measurement techniques were also studied. The concretes were exposed to different initial curing conditions, firstly covered in plastic sheeting for one week followed by exposure to 50 % RH (20°C) or completely sealed post casting and placed in the same climate chamber. Some of the w/c concrete cubes =(0.38) were sealed. One of the aims was to document the self-desiccant effects of the low w/c concrete. At w/c = 0.50, there was no long-term benefit of adding GGBFS in terms of RH measurements up to 6 months, both in the sealed and exposed specimens. The difference in RH in exposed cubes was ca 6% lower than the sealed one. On the other hand, the rate of deliquescence (moisture absorption) from CaCl2 (MVER) indicated a progressive rate drop in water vapour emissions down to 9 lbs/ft2 24hrs with the addition of GGFBS (compared to ca 12 lbs/ft2 24 hours in the reference). At w/c = 0.38, the initial reduction in measured RH is significant with the inclusion of GGFBS (ca 4-6 % lower). After 14 days the highest measurable RH (w/c = 0.38 + 25% slag) was 82 % and the lowest 78 %. Sealing the cubes (after 7 days) stopped the RH evolution in the concrete with slag but not the reference concrete. MVER measurements were very similar in both cases and progressively lowered to 5.7 to 6.9 after 6 months. In the completely sealed specimens (metal buckets with lids), the internal RH dropped at a slower rate than in the specimens that were enclosed with plastic sheeting. The internal RH in the concrete with w/b 0 0.38 and slag remained constant at ca 82 % from day 14 and onwards. In the case of the reference this drop stagewise and were within 1 % of each other after 6 months (83.7 %). The w/b series = 0.50 had no significant development over 3 months and was at approx. 90 %. After 6 months a drop in the measured RH was noted in the slag concrete to 86.1 %. This project even included provision for two RISE /CBI employees to attend the RBK theoretical course which both passed. The practical exam was deemed unnecessary to complete.