What is Lime? (sourced from the BLFI)
Lime has been used as the principal binder for mortars and plasters for the past 10,000 years. The earliest surviving example dates from around 8000 BC in a floor in Turkey. It was only the introduction of cement in the middle of the 19th century, which led to the decline in the use of lime, culminating in its virtual disappearance by the mid 20th century. Emerging evidence in the 1970s of the damage caused to historic buildings by the use of cement mortars and modern plasters has led to a revival in the use of lime over the past 20 years, not only for conservation but also for new build, see Why Use Lime.
There are two principal types of lime
1. Pure Lime which is also known as:
2. Hydraulic Lime, synonymous with water lime, as it sets under water
The production process is interesting. First, quicklime is created by
burning limestone, marble, chalk or shell at above 900ºC to drive
off carbon dioxide. If the material being burnt is pure calcium carbonate,
then pure quicklime is produced. If the material being burnt contains
impurities, typically aluminium and magnesium silicates, then hydraulic
quickime is produced.
When lime is mixed with an aggregate, lime mortar is created. Lime plasters normally also have animal hair added.
Pure lime mortars and plasters made from putty or powder can be used for many building purposes other than externally in exposed positions. Putty is generally considered to be more reliable but provided mortars and plasters made from powder are allowed to mature for a few days prior to use, satisfactory results may be achieved. An accelerated chemical set can be induced in pure lime mortars and plasters by the addition of pozzolans, such as clays, brick dust or volcanic ash which provide the necessary silicates.
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