Lime is made by burning limestone to produce quicklime which is then slaked with water. The resulting putty or powder is mixed with sand to make mortars, renders and plasters. The plasticity of lime, its compatibility with stone and brick, the simple technology of its production and the ready availability of the raw materials (limestone, chalk, marble, coral and shell) has made it an essential and valued material for traditional building throughout the world.
What is the difference between putty lime and hydraulic lime?
Putty lime is made from high calcium raw materials like pure limestone, chalk and shell. It only hardens by reaction with carbon dioxide in the air. Putty lime and putty lime mortars can be stored indefinitely in airtight conditions. Hydraulic lime is made form clay bearing lime stones which make a type of lime which sets by reaction with water. Hydraulic limes have higher compressive strengths than putty lime and harden more quickly.
What are the benefits of lime compared with cement?
Portland cement based mortars are hard and dense with low moisture permeability. These characteristics are not compatible with lime stones, sandstones and brick which are usually soft and porous materials. In fact cement based mortars can damage such materials. It is now widely recognised that traditional buildings constructed of stone and brick benefit both physically and aesthetically from lime mortars, renders and plasters.
How should putty lime be stored?
Putty lime should be stored in airtight conditions. Traditionally it was stored in pits covered with a layer of water. Nowadays putty lime is usually stored in plastic tubs or polythene sacks.
How should hydraulic lime be stored?
Hydraulic lime powder should be stored in sealed bags in dry, well ventilated conditions and used within 6 months of date of manufacture.
Which sands and aggregates should I use in mortars, plaster and renders?
Clean well graded sands are essential for successful mortars, plasters and renders. Carefully graded crushed limestone and chalk can also be used in formulations for traditional and historic buildings. Study of historic mortars can be useful in determining the correct aggregate for a given situation.
Lime is a strong alkali and a caustic material. It can burn the skin and is very dangerous to the eyes
Goggles and protective clothing are essential when slaking lime and handling lime putty. Mortars, plasters and renders when handled correctly do not present an undue hazard. However all lime based materials should be handled with caution.
You should take the following precautions:
- Avoid all prolonged contact of lime with the skin and wear adequate protective clothing
- Always rinse skin thoroughly after contact with lime
- Avoid inhalation of lime dust especially in areas not properly ventilated
- Avoid contact of lime with the eyes
If the eyes or skin have been in contact with lime or products that contain it, clean with fresh water applied in abundance. If irritation persists seek medical assistance.
If lime is ingested drink cold water or milk with one or two raw eggs or fruit juice or 1:2 vinegar: water. Seek medical assistance.
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