Sump lime
Pit lime is a slurry (suspension) of calcium hydroxide (Ca (OH) 2 , hydrated lime , slaked lime ) in water . The name sump lime comes from the very old technique of soaking the lime in a pit after the quicklime has been quenched with excess water.
If the pit lime is pulled out of the pit after months or years, it is fine and pliable, but relatively firm, and the so-called lime sinter water has settled above the slaked lime .
Limy , marsh or fat lime , the tough doughy called up yoghurt type suspension which was mixed with a little water. Is diluted further, one finally obtains the aqueous these milk of lime , as lime wash ( lime paint can be) used. Samp lime with three to a maximum of four parts of sand results in lime mortar for walls and plastering . Diluted mortar or lime milk with added fine sand is called lime slurry .
properties
Manufacturing and setting
For the production of sump lime, the quicklime was traditionally mixed with two and a half to three times the amount of water. The quicklime reacts to form slaked lime (calcium hydroxide or hydrated lime) with strong heat development . If the heat is not removed quickly, the mixture begins to boil and the suspension appears like a boiling, thick soup.
Quicklime and slaked lime are strongly basic substances. Even small splashes of quicklime can seriously damage the eyes.
When slaking quicklime by hand in the form of lump lime, so-called "lime sparrows" are formed, which can be found in many historical masonry mortars. Lime sparrows are undesirable when slaked lime is used as lime paint and plastering mortar, as they cause subsequent erasure and small defects in the mortar or paint layer. A relatively long storage period is required until all crystallization processes are completed, which ultimately determines the quality. The name is derived from the prolonged soaking in limestone pits.
Today, ground quicklime is usually extinguished "dry" without excess water. So-called white lime hydrate is obtained in powder form and post-reactions largely take place. For processing, the powdery calcium hydroxide is mixed with water. Since it is poorly soluble , the result is a suspension.
Pit lime is heavily diluted to produce lime paint . To do this, the thick lime paste is mixed with water until it is translucent and milky and the metal still shines through on a knife blade (craftsman's rule).
After the milk of lime is applied to the painting surface, the calcium hydroxide sets. It absorbs carbon dioxide from the air, releases water and reacts to calcium carbonate , i.e. limestone .
Tinting
Only lime-fast pigments are suitable for tinting . If no other binders are added, only pastel shades can usually be achieved, as pure calcium hydroxide can only bind a pigment content of around 5%.
safety instructions
| safety instructions | ||||||||
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1305-62-0 |
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Calcium hydroxide is irritating and can cause serious eye damage, so it is advisable to use suitable protective equipment (e.g. gloves and protective goggles ) for processing . Although most of the calcium hydroxide is suspended in the lime slurry, some of it goes into solution. The aqueous phase of the pulp therefore has a strong alkaline reaction , irritates the skin and causes burns on prolonged exposure. The mucous membranes and eyes are particularly sensitive . Set lime is as chemically inert as limestone.
Pit lime must be stored tightly closed and must not be stored in aluminum containers ( corrosion ).
use
construction materials
Pit lime is the binding agent of a lime mortar (or lime plaster ), or is used purely as a lime paint ( mineral paint ).
mosaic
Certain mosaic-laying techniques use a mixture of lime and fine river sand and water as a temporary base. This base remains elastic and soft for weeks and months if it is covered with a plastic film between working hours so that the mosaic stones can be set over a longer period of time. At the end, the mosaic is lifted out of the lime-sand mixture by means of a layer of gauze glued to the front with water-soluble adhesive and placed on the final base (often cement ), the gauze is then removed.
restoration
In the restoration, special emphasis is placed on long periods of swamp , and the lime, which is sold as church lime, is stored in the lime pit for 20 to 25 years. With high quality, these limes reach prices that are a multiple of the price of building limes over the years.
For the restoration of buildings, sculptures and sculptures, lime paint is specially mixed with the existing lime materials, and there are countless recipes: In addition to water and calcium hydroxide, which are mixed in ratios between pasty 1: 3 and watery 3: 1 depending on the area of application, there are various Use of additional binders ( saccharides , organic glues , acrylates ) and additives such as champagne chalk or titanium dioxide , which also tint white, as well as additional pigments .
The sump lime can then be used as sintered lime water (for fresco paints ), wall paint , lime slurry , lime filler or lime plaster . For the latter, fine sand is added, others also marble flour , and the processing strength becomes thicker. Specially adjusted lime-based materials harden faster or slower, adhere well to the substrate, show little chalking (are smudge-proof) and a low surface tension.
As a chemical
The term milk of lime is used in chemistry. There it represents a dilute suspension from which, after filtering, lime water , i.e. a saturated calcium hydroxide solution, is obtained. This serves for the simple detection of CO 2 ( carbon dioxide ).
Lime milk has a germicidal effect due to its alkaline reaction and was previously also used for hygienic reasons for whitening walls in animal stalls. Lime water was also used for the makeshift sterility of early medical facilities, abortions, or storage sites for cadavers and for leather tanning.
In chemistry , milk of lime is used for many processes in which the alkalinity is needed to set acids . For example, large quantities of milk of lime are used in water treatment for deacidification and decarbonisation and in flue gas desulphurisation for many wet processes.
advantages
Lime plaster and lime paint are cheap, moisture-resistant, have a disinfectant and fungicidal effect . Mold cannot survive on lime plaster and lime paint because they are highly alkaline.
Pit lime does not require any synthetic substances, neither in the production nor in the form of additives such as B. against mold growth. It is therefore very environmentally friendly. However, it is strongly alkaline and must not get into the soil or water. After it has set, lime paint is hardly water-soluble, so washing it out does not pose any environmental risk. Acid rain can dissolve them, but not in large quantities in a short time, and the resulting solution is then not strongly alkaline.
disadvantage
Lime is very sensitive to discoloration from iron ( mold stains ) and sulfates , i.e. in the area close to the ground. In particular on substrates containing gypsum , there is efflorescence and - because gypsum is hygroscopic , but calcium carbonate is hydrophobic - sulfur corrosion (conversion of lime into gypsum).
The lime's susceptibility to drying out too quickly make it unusable in warm weather and especially in direct sunlight. In addition, it does not tolerate temperatures below 4 ° C during the setting time. These limitations in processing times have meant that it has meanwhile been almost completely displaced from commercial construction. Innovation common in outdoor areas.
See also
literature
- Kurt Wehlte : Materials and techniques of painting. Otto Maier Verlag, Ravensburg 1967, ISBN 3-473-48359-1
- Kurt Schönburg: Natural substances on buildings, properties, application ,: Editor: German Institute for Standardization eV -DIN-, Beuth Verlag, 2010, 280 S. ISBN 978-3-410-17355-7
Individual evidence
- ↑ Sumpfkalk. In: Angela Weyer et al. (Ed.): EwaGlos. European Illustrated Glossary Of Conservation Terms For Wall Paintings And Architectural Surfaces . English Definitions with translations into Bulgarian, Croatian, French, German, Hungarian, Italian, Polish, Romanian, Spanish and Turkish. Michael Imhof, Petersberg 2015, ISBN 978-3-7319-0260-7 , p. 388 , doi : 10.5165 / hawk-hhg / 233 ( download ).
- ↑ Albert Knoepfli; Oskar Emmenegger: Wall painting up to the end of the Middle Ages. In: Reclam's Handbook of Artistic Techniques, Volume 2, Wall Painting and Mosaic. Philipp Reclam jun. Stuttgart, 1990, ISBN 3-15-010345-2 , p. 36.
- ↑ Friedrich-Wilhelm Borchert, Udo Steinhäuser, Werner Schulz: Brick factory history (s): former brickworks on Lehm- und Bricksteinstraße , p. 65; BoD - Books on Demand, 2011.
- ↑ a b Entry on calcium hydroxide in the GESTIS substance database of the IFA , accessed on July 29, 2017(JavaScript required) .
- ↑ Wehlte, chap. 3 Materials of Wall Painting , p. 209ff.