Lime mortar
The lime mortar is as a building material, a mixture of slaked lime and sand and is classified according to composition into several mortar groups (MG) .
Composition
The term lime mortar (MG 1) does not refer to a part of the material, because it contains no (or hardly ) lime ( CaCO3), but slaked lime (Ca ( OH) 2). Furthermore, it is known as lime mortar also for processing mixed with water, material containing the dry reaction product of the quicklime with water (commercially also known as hydrated lime ), it falls to DIN 1053 ( masonry DIN ) into the mortar group MG 2a lime mortar / hydraulic mortar (compressive strength 2.5 MN / m²). For direct processing of burnt, but ungelöschem lime, where the deletion takes place so when mixing the mortar, one speaks of Heißkalkmörtel - this building material has primarily historical significance.
Typical mixed Verhältnise for lime mortar 1:2 to 1:5:
An addition of mixing water is because in slaked lime water is already bound, necessary in small quantities
With the additional use of cement -lime mortar, the mortar 2b falls in the group MG ( up to 5 MN / m²) Other adjuvants such as plaster or masonry cement ( resin binders ) are possible.
Setting process
After applying the slurry, mixed with water, it binds the mortar gradually. The calcium hydroxide (Ca (OH ) 2) goes beyond with carbon dioxide (CO2 ) of the air to lime (CaCO3):
( Partial reaction of the technical Kalkkreislaufs )
This process takes place but only in the presence of air. Therefore unprocessed lime mortar is kept wet so that it does not harden. The temperatures should be above 5 ° C, but not above 20 ° C, otherwise the mixing water evaporates too quickly and also decreases the CO2 content of the water with increasing temperature.
The forming fine, needle-like calcium crystals bind the sand component with which they become matted so that the mortar forms a hard, coherent solid. Therefore, a calcareous Price ( limestones, dolomites) is the most suitable, since it takes place in a chemical bond between the calcite crystals of Fettkalks and sand. Quartzose sands make the stuff though harder but less elastic, because the softer calcite structure bears the main burden, and the grains are mechanically linked.
The full completion of this process may take many years. It can be accelerated by increasing the carbon dioxide concentration in the ambient air, for example, by combustion of organic material ( such as coal fire). In some particularly thick walls of ancient castles, the mortar is partially not yet set today. The delays setting in particular also by the fact that on the surface of a sintered layer of a few micrometers thickness is composed of highly crystalline, pure calcite ( which is highly transparent, this principle allows the fresco technique of mural painting ). However, this layer impedes the diffusion of CO2 into the interior, and hence the Auskarbonatisieren.
Properties and Uses
Lime mortar is less pressure resistant than water mortar (for example, cement-based mortar) and is therefore suitable only there for bricklaying ( mortar ), where no high pressure resistance is expected. Lime mortar ( without cement additive) effect but good moisture-regulating and can therefore be used for interior plasters.
In addition to the local climatic advantages lime plasters and mortars have to cement plasters also environmental benefits, eg in natural stone masonry for the insects that live there and for the CO2 budget. The expelled in the production of lime from limestone CO2 is taken up during the curing process. The balance sheet is so balanced as opposed to cement mortars, which are also made mostly of limestone; here will be no CO2 uptake. Not taken into account is the CO2 emission, which is caused to obtain the process heat in this balance. The cement industry is responsible for about 4-5 % of global CO2 emissions.
Norms and Standards
- DIN 1053 - Masonry
- DIN 18550 - Plaster and plaster systems