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Why we use Lime in modern and Historic building
Historic buildings proving the point of why lime is crucial in construction & healthy living.
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.
Sustainability
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 plaster, as well as burnt to supply fresh lime for building. Eco-friendly and carbon footprint reducing.
Main Building Limes
Hydrated lime - A white powder construction binder. Weakens cement to a more palatable strength for conservation work, but fails for building when used on its own, hence the need for lime putty & hydraulic lime (NHL)
Hydraulic Lime (NHL) A white powder construction binder. The precursor to cement, mixed with sand & water (latin: water = hydrau) to create a masonry bonding material without the need for cement.
Non-Hydraulic Lime (Fat Lime / Putty) A putty construction binder. White, doughlike, putty mixed with sand (no water = non hydrau) to create a masonry bonding material. The original bonding material for construction before the advent of hydraulic lime & cement .
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.
General Mix Ratios
Plasters contain more lime than Mortars, but mix ratios are defined by the particle size for binding, the need to adhere to substrates,or to bring out the colour of the sand .
Depending on the aggregate particle size, 'the more fines,the more lime' needed. Sand to lime ratios (sand : lime) are generally, Mortars 3:1, Renders 2.5:1, Plasters 2:1
Plasters may sometimes be richer in lime for adhesion, mortars leaner in lime for colour
Stone work & Renders - 4mm sharps sands
Brick work & External Plaster - 2mm sands
Ashlar Stone & Plasterwork