Water extraction out of mortar during brick laying : a NMR study

The water extraction out of mortar during brick laying was studied using nuclear magnetic resonance. The experiments show that using a fired-clay brick, the water is extracted out of the mortar within 3 minutes, whereas in the case of a sand-lime brick this takes about 10 minutes. Prewetting a fired-clay brick hardly affects the water extraction, whereas prewetting a sand-lime brick slows down the water extraction, although the effect is small. The extraction process is slowed down only if the bricks are almost fully saturated. These effects are explained with the help of computer simulations. The final moisture content of the mortar is shown to depend on the suction of the brick and thereby on the equilibrium moisture content of the brick. By adding a water retention agent to the mortar, the extraction process seems to slow down, although the final moisture content of the mortar is not changed. The water extraction experiments suggest that the suction of the mortar which is formed depends on the water extraction rate and thereby on the type of brick that is used in the extraction experiment. Petrographic analyses indicate that the extent of bonding between the brick and the mortar is different for fired-clay brick and sand-lime brick