CaLoSiL® contains nano-particles of lime hydrate [Ca(OH)2] suspended in different alcohols. Typical concentrations are between 5 and 50 g/L. The average particle size is 150 nm. The extremely fine size of the synthetic nano-lime results from its preparation, which is based on chemical synthesis. Ethanol, iso-propanol or n-propanol serve as solvents. Due to the low particle size stable sols are formed which do not sediment for a long time.
CaLoSiL® is a ready-to-use stone and plaster consolidant. Treatment of stone, mortar or plaster with CaLoSiL® results in the formation of solid calcium hydroxide after evaporation of the alcohol, that converts into calcium carbonate in a way similar to traditional lime mortars by reaction with atmospheric carbon dioxide. All alcohols evaporate without any residues so they do not harm the stone or plaster. Chemicals or residues deteriorating stone or mortar are not formed.
CaLoSiL® can be applied using either a flow coating procedure, by dipping, spraying or injection. It is important that the complete weathered zone of the stone down to the sound is treated.
CaLoSiL® is available in concentrations between 5 and 50 g/L. The letters behind the name “CaLoSiL®” indicate the used solvent, the numbers give the total calcium hydroxide concentration in g/L. E –stands for ethanol, IP for iso-propanol and NP for npropanol. For example, E-25 means, 25 g/L calcium hydroxide dispersed in ethanol.
The calcium hydroxide particles formed after evaporation of the alcohol cover the surface of treated cracks, pores or joints. Dense films of calcium hydroxide films are formed, depending on the number of treatment cycles and the concentration of the used sols. Typical particles sizes are in the range of few hundred nano-metres. Their detection by means of standard optical microscopy may be difficult, the use of SEM is recommended.
Calcium carbonate formation by reaction with atmospheric carbon dioxide requires the presence of humidity. Depending on the conditions and the amount of calcium hydroxide brought into stone, mortar or plaster carbonations takes place within few days and weeks. After spraying the treated materials with water the carbonation process can be accelerated.
The penetration into mortar, stone or plaster depends on the following factors:
- Characteristics of the CaLoSiL type applied
- Structure and surface characteristics of the materials to be treated,
- Porosity and capillary rise,
- Moisture content of the material
- Air temperature and air humidity during the application
When dense materials are treated with highly concentrated CaLoSiL products (CaLoSiL E-50, CaLoSiL-paste like etc.) the penetration behaviour may be only slow, especially if there aredense surface layers such as gypsum crusts which prevent its penetration.
High moisture content also inhibits penetration so when necessary pre-wetting with ethanol may help to reduce the moisture content of the material.
White haze formation
The formation of a white haze on the surface of the treated material depends not only on the penetration behaviour of CaLoSiL but also on the evaporation conditions of the alcohol, which can re-transport nano-particles back to the surface. In addition if too little time is allowed for carbonation of the nanolime within the treated material it will not be fixed in place and can be transported to the surface. General rules to prevent / reduce the formation of white haze are:
- Start the treatment with low concentrated products, increase the calcium hydroxide concentration step by step
- Avoid the treatment of wet materials, reduce the moisture content by pre-treatment with ethanol or ethanol-water mixtures (1:1).
- In the case of sensitive surfaces try to use CaLoSiL grey, which has a special consistency allowing deep penetration without white haze formation
- Avoid an “oversaturation” of the treated stone, plaster or mortar. Remove all CaLoSiL which could not penetrate into the treated material for example, with a sponge.
Mixability with other materials
All CaLoSiL®-products can be intermixed. Blending with ethanol, n- or iso-propanol is also possible without any difficulties. However, the addition of water can result in the formation of a gel because of flocculation of calcium hydroxide particularly when the amounts of water is greater than 10% by weight.