The use of lime putty mortars externally during the winter months is not advocated, and certainly not when the temperature is below 5°C and falling. External work should be scheduled to avoid the period from October to March.

Animal hair has been added to strengthen and reduce shrinkage in lime plasters for centuries and is particularly important when applied to laths.

Lime plastering to solid masonry walls can be carried out in one, two or three coats. Three-coat work is normally necessary on uneven masonry. Two-coat work is often sufficient on flat surfaces such as brickwork. One-coat work is coarse textured finish plaster reserved for medieval and early buildings.

There is renewed interest in hot-mixed non-hydraulic lime mortars with many proponents being of the view that lime mortars prepared in this way have advantages over the normal practice of mixing lime putty and sand.

Traditional lime mortars carbonate ‘within’ as well as on the surface. Two groups of aggregate have a positive chemical effect on mortar performance, Calcareous or limestone aggregates and pozzolanic materials.

The Blending of Hydraulic and Non-Hydraulic Lime. The current situation is that it is agreed that a small proportion of non-hydraulic lime (either as hydrate or putty) can be added to hydraulic lime mortars to improve workability, but it must be understood that a reduction in strength of mortar will result.

Historically, Shillingstone, Totternhoe, Dorking and many other limeworks produced ‘lean limes’. These combined the good working properties of non-hydraulic ‘fat’ lime with some slight hydraulicity. Sadly, no traditional lean-lime plant is currently in operation.

Lime Putty used for the production of lime mortars, plasters, and renders must be of the best quality and the ageing or ‘maturing’ of non-hydraulic lime putty is an essential part of the production of best quality material.

‘Tempering’ is the practice of allowing Lime putty mortar to stand undisturbed for a period of time in the wet state before use.

Limewash and Distemper have a beauty hard to match with modern paints. They possess softness of texture and purity of colour lacking from their modern equivalents.

Limewashes are thin dilutions of non-hydraulic lime, water, and alkali-fast powder pigments. Exterior grade limewashes have additional binders – casein, tallow or linseed oil – to improve performance and durability.

Non-hydraulic lime putty internal plasters are soft, porous and permeable. These are the materials used historically to plaster traditional buildings and are normally appropriate for re-plastering and plaster repairs.

Non-hydraulic lime putty mortars are soft, porous and permeable. These are the mortars used to build most traditional buildings and are therefore normally the appropriate materials for the repair of these older buildings.