Top Tip

Top Tip

A lime binder either in a plaster or render mortar must be cured once it has been applied because it needs time to fully hydrate, to allow it to acquire strength and hardness. 

Good curing requires a moist environment which promotes hydration. Increased hydration in any mortar lowers permeability and increases strength, because more mechanical bonds are created with the mortar.

Excessive quick drying of lime (hydraulic or none hydraulic) plaster, even after it has been left in a wet state on a wall or ceiling for months, will cause failure, which may not show for months to come.

Where a plaster or mortar is allowed to dry out too quickly, hydration and carbonation of the binder is prevented, resulting in a weak and friable mortar. Plastic shrinkage is the consequence of the rapid evaporation of an over wet mix causing cracks to appear quickly but a lack of hydration and carbonation throughout the depth of a plaster is much more serious and can cause failure.

Always ensure lime or indeed cement based plasters and renders, cure by drying out slowly, in warmer environments this may mean dampening down the plaster once or twice a day.  This is still the case for plaster in an unheated building, in a cold damp environment at this time of year. Nothing can be done until the environment is heated or warms up but at this stage even months later the plaster must be dampened down as it dries out, especially if excessive heating is introduced on site to get the job finished and decorated.