Lime Plaster
Lime plaster having gone through the carbonation process reverts back to limestone. Therefore plaster with lime and you are effectively applying a thin sheet of limestone to any shape or colour which can be polished to give a rich and smooth colourful surface.
The Lime Cycle
- Calcium Carbonate - CaC03 (In the form of sea shells or limestone)
- Heated to 800°C - Carbon Dioxide given off
- Leaves Calcium Oxide Ca0 known as quicklime.
- Water added to give calcium hydroxide Ca(0H)2 known as slaked lime - used in lime plastering.
- Mixed with sand and applied to walls, ceilings or floor.
- Back to limestone! - As water content decreases carbonation occurs - carbon dioxide combines with the lime to create calcium carbonate. Ca(0H)2 calcium hydroxide + C02 Carbon Dioxide = CaC03 Calcium Carbonate + water H20
Calcium Hydroxide combined with aggregate applied to floor, walls and sink
Calciul hydroxide carbonates to form Calcium Carbonate (limestone)
A Few Benefits of Lime Plaster
- Porous allowing water to be absorbed from the surrounding materials, thus protecting them from the harmful effects of frost and hygroscopic salts.This is particularly important for soft brick and stone.
- Help to control condensation and damp by allowing building to breathe.
- Flexible and so allows a certain amount of movement unlike hard and brittle cement mixes.
- When small cracks do occur they can self-heal.
- A soft, natural appearance that it well suited to the character of old or unique buildings.
- Although lime is caustic and needs to be handled with care, it does not contain volatile organic compounds or other chemicals that are often found in modern materials.
- Can be polished to form a waterproof yet breathable finish.
Lime can heal itself – self healing or auto healing
If as a result of movement a crack forms then Self healing can take place.
Lime like stone has pores which are very small channels that allow the passage of air through and therefore allows the wall to breathe.
The absorption of carbon dioxide and moisture present in the pores forms carbonic acid that combines with the calcium present in lime to form calcium carbonate crystals that will grow and mend the crack (as long as moisture is present). However Carbon Dioxide is required so if there is too much water then the Carbon dioxide cannot flow and this process will not happen. Hydraulic lime contains silicates which do not contain pores and therefore don't allow this process to happen as much. Lime putty will allow the most self healing whereas a hydralic lime NHL 5 will self heal less.