Will pre-wetting brick masonry units increase the rate of moisture expansion in clay masonry walls?
Clay masonry units with a high initial rate of absorption are sometimes pre-wetted to improve mortar bond. I am not aware of any studies that conclude that pre-wetting clay brick units will affect brick masonry's rate of moisture expansion. Moisture expansion is a relatively slow process. Most moisture expansion will occur the first year after the brick masonry walls are constructed and taper off thereafter. Interior clay masonry walls also will grow from moisture expansion. Although they are not wetted, they absorb moisture from air over time. Since moisture expansion occurs over a long period, it's unlikely that pre-wetting units will have a significant effect. Moisture expansion is a permanent, irreversible expansion of clay masonry units. It must be taken into account when designing and detailing clay masonry walls in any exposure. Moisture expansion is accommodated by the use of both horizontal and vertical expansion joints. Concrete brick should not be pre-wetted. All concrete masonry units expand with wetting and shrink as they dry. Thus, the pre-wetting of concrete masonry increases shrinkage as units dry. An alternative for hot, dry conditions is to fog spray concrete brick after they've been laid to prevent the mortar from drying out.