How to protect curing Lime Mortar
Protecting and providing aftercare to lime mortar is important all year round but particularly if work is carried out in the winter, when frost may be a problem, or in the summer when the mortar dries out too quickly.
Curing is the process of keeping a mortar or render under a specific environmental condition until the chemical set is sufficient to withstand the environment into which the mortar has been placed.
The most common cause of failure is allowing a mortar/render to dry out too quickly, impeding the chemical process for hydration, stressing the mortar and resulting in cracking
Freeze Thaw Action: Freeze thaw action can only occur if the mortar is fresh or saturated. If there is a danger of freezing of fresh or uncured mortar, cover the mortar with hessian. Hessian can be layered up to provide additional protection. Temperatures below 5C slow the carbonation and hydraulic setting process and frost conditions will damage un-cured areas, resulting in feeble and crumbly finishes.
Rapid Drying: If the mortar dries out too quickly, hydration and carbonation will be inhibited so stressing the mortar. Stressed mortar may suffer shrinkage, cracking and separation from the background. Avoid by screening against direct sunlight by using wet hessian close to the wall so protecting the mortar from drying out too rapidly by creating a humid environment. Also keep the work moist (not wet) by use of pump sprayer.
Variances in saturation of the walls will cause differences in curing times. Don’t be surprised if the mortar applied to the lower section of a wall takes longer to cure than other areas. Be reassured that the lime mortar is already doing its job of absorbing excess moisture from the surrounding masonry and releasing it to the atmosphere.
Both warm and cold weather can result in whitening on the surface. This is caused by some of the lime being drawn to the surface. Hessian protection should avoid this happening but if it does occur just brush away with a churn brush.
Hot lime and non-hydraulic limes will need protection for longer than hydraulic limes to ensure they are not damaged. Leave the hessian protection up for at least 10 days over these types of mortar.
Use of hessian close to the wall creates a microclimate that can raise the temperature a few degrees in colder weather and wet hessian will reduce the temperature a few degrees in hot weather.