An interior finished with traditional lime plaster makes for a healthful living environment. Lime plaster has long been a valued construction material, and is used indoors and outdoors. Lime is extremely alkaline and thus plaster is widely used in damp rooms (it is mildew-proof and withstands moisture). Walls in any room can be rendered with lime plaster: old log houses, modern new homes, prefabricated concrete panel apartments, cellars, etc.
Properties of lime plaster
- It’s a great solution for those with allergies, as it is odourless and its high pH (ca. 13) makes it unsuitable for bacteria or mould.
- Lime plaster has good breathability and ensures a balance in relative humidity.
- According to certificates from the American Society for Testing and Materials, lime is free of volatile organic compounds (methane, aldehydes, ketones, etc.).
- Lime plaster is antistatic, meaning that walls will be dust-free; this will reduce the amount of airborne dust and less will be breathed in.
- It is also bleach-proof, which means it will look just as fresh as on the first day, keeping repair costs low.
- Freezeproof and waterproof, and thus widely used for finishing outdoor surfaces. But lime plaster only has this particular quality if it has been given the proper final finishing coat!
Lime plaster can be used for many different kinds of surfaces
- reed board
- wood (in this case, first cover the surface with reed mat or reed board)
- light concrete
It is advisable to apply three or more layers of plaster, making sure that none are more than 8 mm thick. Excessively thick layers of plaster and too rapid a set are the main reasons for cracking. In interiors, the total thickness of the plaster layers must be at least 2.5 cm; outdoors, 4-8 cm.
When starting a rendering project, make sure the average temperature over a 24-hour period is over +5 C and plan one month for a 10 mm layer to carbonise. That means that outdoor work should be completed by late August or early September (this varies by year) so the surfaces can harden before the cold sets in. Work performed at temperatures lower than +5 C will lack quality and the plaster will crumble off the wall.
Traditional lime plaster for indoor and outdoor use is made of high-quality lime putty and construction-grade sand. The lime putty must have been aged for six months. Today good Estonian-made lime putty is available. Lime plasters that were made from slaked lime powder will not produce the same results in terms of either quality or workability. Thus we advise the use of lime putty for preparing the plaster. We also use it ourselves.
The plaster gets its final appearance from various finishing methods and materials. The result is a distinctive, even unique interior. We choose the finishing method and possible materials based on the customer’s vision. In the finishing phase, lime plaster can be made completely hydrophobic, making it possible to use it in rooms where water splashes or condenses on walls.
Lime plaster rendered surfaces must not be covered:
- with latex, oil, alkyd or polymer paints
- polymer plasters
- cement plaster
The explanations of all of the terms below were taken from the EVS 763-1: 2000 standard.
- Lime is a material consisting of different physical and chemical compounds and containing calcium and/or magnesium oxide CaO and MgO) and/or calcium or magnesium hydroxide (Ca(OH)2 and Mg(OH)2).
- Building lime – limes used in construction structures and the construction process.
- Air hardening lime – mainly calcium oxide or hydroxide, hardens slowly in presence of atmospheric carbon dioxide, generally does not harden under water, air hardening limes can be slaked or unslaked lime.
- Quicklime – air hardening lime consisting mainly of calcium and magnesium oxide formed by thermal decomposition of limestone and/or dolomite, and is found in different grades from large chunks to a finely ground powder.
- Hydrated or slaked lime is an air hardening lime that is obtained by mixing unslaked lime with water. Slaked limes are produced as dry powder, a lime paste or suspension (milk of lime).
- Natural hydraulic lime is obtained by thermal decomposition (at temperatures under 1250 C) and slaking of limestone with varying concentrations of clay and silicon). All natural hydraulic limes have the property of partially solidifying and hardening in water. The process is accompanied by the hardening of lime from the CO2 in the atmosphere. Special products may include up to 20% siliceous or hydraulic materials.
- Hydraulic lime is made of suitable raw ingredients, primarily calcium hydroxides, calcium silicates and calcium aluminates. Has the property of solidifying and hardening in water. The process is accompanied by the hardening of lime from the CO2 in the atmosphere.