These sands increase the density of mortars and renders, aggravating water retention problems. Walls breath better and moisture can evaporate. Mortars and renders do not set too hard. Thermal movement can be accommodated without damage. Expansion Joints can be avoided.
Insulation is improved and cold bridging reduced.
Reduced risk of condensation. No risk of salt staining. Alterations can be effected easily and masonry revised. Masonry life is increased. Hydraulic limes on the other hand provide a quick set permitting building work to proceed rapidly - on a par with cement and do have a significant degree of flexural strength, permitting its use on thin skinned buildings.