Sectors | HeritageHeritage Featured

Mortars, Renders and the use of Lime

4 January 2018 | Sectors | Heritage, Heritage Featured

Over recent years there has been much discussion about the design of mortar and renders. Are you confused? Should you use cement, cement lime, lime putty, hydraulic limes, hybrid limes or hot mixed mortars?

Each of these has its place in the appropriate specification of mortars and renders in buildings. The correct specification will depend on factors that include the required appearance, the structural load and the poulticing effect, which controls moisture levels in the wall.

In buildings of historic significance, matching the original mortar is an important consideration and the volumes of mortar are likely to be small. In new-build construction, the volumes are likely to be high and the rate of construction also high. The stresses in our modern thin-walled construction are also higher, which almost always adds the criteria of strength to the designs of mortars.

A well-designed mortar should be workable, cohesive, adequate but not too strong, frost resistant and vapour permeable. It should stiffen at a reasonable rate. As the mortar represents between 15% and 30% of the area of the wall, it is an important factor in the overall appearance.

The choice of binder is important but so is the aggregate as this will be a critical element in the strength, permeability and frost resistance.

To learn more contact James Miller at CTP.