Lime mortar was man's first real good building cement.
A SHORT HISTORY OF LIME MORTAR
Lime must has been discovered soon after man learned how to use fire and then to make fire when ever desired. When using stone for building a place for his
fire, man soon learned that not all types of stones should be used for fireplaces. Limestone is one, because it sends out out hot gases and sparks when heated.
And if heated hot enough, limestone turns into a white powder. When water is added, the white powder becomes quite hot before cooling into a harden mass.
At some time, two or more rocks became cemented together in the fireplace. Someone then discovered by experimentation that the addition of clean sand
reduced the amount of lime required and decreased the hardening time. Those unknown early builders decided to use this process to build a better fireplace
or hearth. A permanent one, perhaps with high sturdy walls.
Perhaps from this simple beginning, the art of masonry was born.
The first building mortars developed were then the lime mortars, a slow hardening mixtures of lime, sand, and water.
The development of Portland cement in 1824 allowed the introduction of a hydraulic binder, which was very consistant and set up rapidly. Its relatively
rapid development of bonding strength was a marked advantage over lime mortars. This was particularly important in situations where there was a risk of frost.
And Portland cement would harden even underwater. Lime mortars can not.
Lime mortar set slowly and hardened even more slowly so builders slowly abandoned lime mortar in favor of the cement and sand mortars.
By the 1830's, the 1:1:6 mixture of cement, lime and sand ratio had been firmly established.
However, cement and sand mortars proved too strong for some applications and lacked some of the workabilty of lime mortar. By the late 1800's cement-lime mixes
were again widely used where increased plasticity, workability and controlled strength was required.
And recently, lime mortars are being widely used again. Lime mortars are especially desired for masonry restoration work on historical mansonry buildings and
ADVANTAGES of LIME MORTARS
Lime mortar has important characteristics:
HOW LIME IS MADE
- High workabilty
- Water retentivity very high. This makes it particularly suitable for use with some applications.
- The lime in the mortar improves adhesion(bonding strength) and reduces rain penetration. (Thereby reduces frost damage to unprotected masonry wall tops)
- In mortars containing lime, carbon dioxide dissolves in water and reacts with lime to produce insoluble calicum carbonate crystals. These crystals form in
spaces such as cracks and grow, thereby sealing the cracks. This self-sealing characteristic reduces water penetration and increases durability. Especialy in
areas where masonry work is prone to frost damage. The rate of carbonation is dependent upon several environmental conditions.
- High placticity, which allows the user to produce a flexible masonry structure, capable of contending with movement resulting from both, thermal and moisture
content changes without cracking. Movement joints are not required since the lime mortar can obsorb the expansion. This reduction in the risk of cracking reduces
problems related with water penetration.
- Lime mortar has a lower structural strength than Portland cement but it insures a lasting durabily, as many old historical building and medieval castles prove.
Lime is produced from limestone through these following steps.
- Quality Limestone, calcium carbonate (CaCO3) is heated until burnt in a kiln or kiln pit. At the temperatures between 800-900 º Centigrade limestone gives off carbon dioxide (CO2) leaving
calcium oxide (CaO) or quicklime.
2 CaCO3 + heat = 2 CaO + 2 CO2 (gas)
CaCO3MgCO3 + heat + CaOMgO + 2CO2(gas)
- The remaining substance (quicklime) is unstable and reacts with water (H2O) to produce heat and resulting in the formation of calcium hydroxide.
CaO + H20 = Ca(OH)2 + heat
CaOMgO + H20 = Ca(OH)2MgO
CaOMgO + 2H2O = Ca(OH)2Mg(OH)2
- Mixing qicklime, sand, or aggregrate, water in the proper ratios produces mason's mortar, which is used to bind blocks, bricks, or stones together.
- On exposure to air mortar sets hard. This is because of the normal curing (drying) and because the lime absorbs carbon dioxide from the air. The
setting of mortar depends upon the formation of a colloidal hydroxide of lime. Following when water is first added, the colloidal substance "sets up"
much like a glue. Then calciun carbonate begins to form.
The sand makes the material more porous and increases the obsorption of carbon dioxide. The
sand also lessens the amount of lime required for a given amount of lime mortar and lessens the shrinkage that takes place as the mortar dries and sets up.
The hardening process of the mortar is the result of the absorption of carden dioxide from the air by the calcium hydroxide in the mortar and reverting into
calicum carbonate. This Carbonation, or setting process, is quite slow and usually takes weeks to complete.
- Portland cement: Isle of Portland, England 1824. Named for its resemblance to a limestone found there. Portland cement is a hydraulic cement made by finely pulverizing the clinker produced by
calcining to incipient fusion a mixture of clay and limestone or similiar materials.
- Cement:A powder of alumima, silica, lime, iron oxide, and magnesium oxide burned together in a kiln, and finely pulverized and used as an ingredient of mortar and cement. This is the binding
agent in concrete.
- Concrete: a strong hard building material made by mixing a cementing material, such as Portland Cement, and a mineral aggregate(as sand and gravel) with sufficient water to cause the cement to
set and bind together the entire mass.
- Masonry Mortar: A mixture of lime or cement with sand and water, used as a binding agent for stones, bricks and blocks.
- Slaked Lime: Calcium hydroxide, Ca(OH)2), a white solid produced when lime reacts with a sufficient amount of water.
- Lime(mineral): Quicklime is composed of calcium oxide(CaO) and is a caustic solid substance, white when pure, obtained by calcining limestone and other forms of calcium carbonate.
Books On Making and Using Lime Mortars
- Lime Mortar Books
This link will connect to Lübeck Haus Bookstore's extensive list of lime mortar books.
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- Lübeck Haus Bookstore Bookstore Page .
Lists books on the history of lime mortars and making and using lime mortars.
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Browse Lübeck's Bookstore's catalogue directory for building with stone and stone contruction books, including lime mortar and dry stack masonry books.
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This page was last updated Frebrary 18, 2020.