WHY USE THE LIME?
WHY USE THE LIME 1
The line of NATURAL CALK offers the customer a full range of lime-based products : their use helps to reduce the thermal load inside buildings requiring less heating; with the aid of solar radiation the lime allows dehumidification and crystallization of fine particles, removing their presence from the weather events, and so preventing the damage of the surface of buildings.
Studies aimed at identifying the most suitable binders to use in traditional buildings have shown that lime, and in particular slaked lime is a material that ensures optimal wall transpiration. This is noteworthy, especially in repairing and restoration of historical artistic buildings .The calcite crystals generated during the carbonation of lime-based products are much larger than those created during hydration of hydraulic binders.
The growth of calcite crystals in the pores coated by supersaturated solution of calcium hydroxide, produces a gradual increasing of resistance in time, conferring high permeability to the mortar. Vice versa, especially in plasters, the thick and impermeable mortar of the cement can trap moisture inside walls, this often triggers and / or catalyzes various mechanisms of deterioration. In the recovery , rigid and less permeable materials can cause serious problems when are brought into contact with weaker and more porous materials, giving rise to high local tensions that can seriously affect the stability of buildings.
When the external and internal plasters are accurately hygroscopic, as those based on lime putty, they are capable to regulate the relative humidity of environments, absorbing and releasing moisture optimally, increasing comfort in the premises, reducing condensation and preventing the onset of moulds . The lime, is strongly alkaline and caustic, and thanks to its antiseptic and disinfectant capacity it has been, and is still used ,to sanitize the environments.
When lime-based mortars and plasters are subjected to vibrations and small movements, they have the tendency to develop many fine cracks; whilst in the case of hydraulic binders, mainly of cementitious nature, the tendency is to develop a few cracks but wider. The mortar and plasters composed of slaked lime, when the water gets into the fine cracks, can dissolve the calcium hydroxide still present and, in presence of carbon dioxide, the calcium carbonate (as bicarbonate), carrying and distributing them. As soon as the water evaporates the carbonate reprecipitates and the hydroxide is deposited. Subsequently they carbonate determining a process known as “sealing”. This phenomenon is known as: autogenous self-sealing of cracks or fissures.
The ultrafine particles (nano-sized) present in the slaked lime of quality and sufficiently seasoned, are able to penetrate more deeply into the tiny gaps of the surface, gently binding themselves, and developing a good adhesion.
The high porosity and permeability of the mortars of slaked lime, once checked the passage of moisture through the masonry (which is the proof that the hygroscopicity is correct), will allow with its application an optimal protection of the roman brick walls and / or stone walls.
It is called workability the capacity of a mixture to maintain good cohesion and plasticity, even when subjected to suction by porous materials, and to be transformed without excessive effort . This property is excellent especially in seasoned slaked limes , and is of great help to get an easy and optimal application of joints, plasters, stuccoes, etc..
The absence of potentially hazardous chemicals, such as tricalcium aluminate and alkaline substances (potassium and sodium oxides), always present in hydraulic binders, makes the mortar of hydrated slaked lime immune from actions of destabilization and expansion of sulfates and from deleterious alkali-silice reactions. Consequently, works that use lime-based binders are extremely durable, as evidenced by many historic buildings, most notably the Pantheon in Rome, which shows that the lime is able to pass the test of time.
The double refraction of calcite crystals gives a unique effect to putty finishes, combining a soft surface texture, with a sheen that gives vivacity and aesthetic pleasure to the mansory.The finishes of putty properly seasoned, have no tendency to detach and skin, but wear and degrade in harmony with the substrate.
The hydraulic lime is cooked at a lower temperature compared to hydraulic binders, and requires less fuel consumption and consequently releases lower carbon dioxide emissions into the atmosphere. Moreover, during the carbonation, practically all the carbon dioxide emitted in the calcination is absorbed and then eliminated from the environment. The lime can be produced locally, further saving energy (for transportation) and environmental benefit.
The different types of limestone produced in various region, will influence the resulting hydraulic limes: color, texture and properties will characterize and enhance the local identity . The lime is a product with an excellent cost-effective also thanks to the coverage capacity by volume: used in plaster, to cover the same unit area, its dosage is up to 50% lower than the hydraulic binders.
The binders made of non-hydraulic lime are the only ones suitable with the materials used for historical and artistic buildings: chemically speaking they do not react with the pre-existing materials and they do not give rise to the formation of unstable, inconsistent, or harmful compounds; as for the physical behavior they present values of elastic modulus, mechanical strength, thermal expansion and porosity, in minor or equal proportions to those of the ancient materials .