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Why we use Lime in modern and Historic building
Lime mortars, renders and plasters have many qualities missing from modern building materials.
Flexibility
Lime products are slightly flexible, in that they will absorb slight movement in buildings, such as expansion, without cracking. A lime mortar will be designed to be the weakest part of a wall, so if there is a violent movement, the mortar will break, not the bricks or blocks.
Breathability
Lime products are more vapour permeable than conventional materials. They allow the movement of water vapour to air. Lime mortar acts as a wick, drawing moisture out of brickwork, stonework and blockwork, reducing the drying time after rain and reducing the risk of spalling. Lime renders will allow any moisture that enters the substrate through building defects to escape through the render, instead of trapping the moisture behind the render, causing delamination of the render.
Carbon production/absortion
Brick and block production creates huge amounts of carbon dioxide. Buildings that use lime mortars can, at the end of their useful life be taken apart and the constituent materials can be used again, reducing the amount of brick and block production needed. Lime mortars, renders and plasters can be crushed to make aggregate for new mortars, renders and plasters.
Main Building Limes
Hydrated lime - Limestone binder. A powder. Weakens cement to a more palatable strength for conservation work, but fails for building when used on its own. Hence the need for Putty & NHL
Hydraulic Lime (NHL) Limestone binder. A powder. The grandfather of Cement. A white / off-white /grey powder mixed with sand & water (latin: hydrau) to create a masonry bonding material
Non-Hydraulic Lime (Fat Lime / Putty) Limestone binder. A putty. The original bonding material for construction before the advent of hydraulic lime & cement . An white / off-white doughlike putty mixed with sand (no water - non hydrau) to create a masonry bonding material
Lime Putty is slower setting, and used in Listed building conservation. Premix needs no water or mixing onsite, but would otherwise require a pan (screed) mixer to create your own mortars and plasters. Packaged in 25kg tubs, or plastic lined Bulk Bags.
NHL is faster setting, and used in building restoration & new build. NHL premix really means pre-blended binder & sand and requires water and mixing on-site, but can be mixed in a Belle Mixer. Premix products may be preferred for consistency & expediency, or because it has specific additives. Packaged in 20kg & 25kg bags.