They are usually classified by their purity CL 70 to CL 95 for the purest. More common in Europe, it has a better reputation for purity and durability. They are classified as Type N (Normal Hydrated Lime) and Type S (Special Hydrated Lime). It contains a certain proportion of magnesium oxide. This is the most common lime used in North America. In this category, we find two different products with different chemical compositions: DOLOMITIC HYDRATED LIME This lime is then called Natural Hydraulic Lime or NHL. If the original limestone contains clay (between 5 and 22%) or silica, this will give the lime hydraulic properties allowing it to begin its set in the presence of water. In this case, the slaked lime produced is called Air Lime or Hydrated Lime. If the original limestone is very pure, the absorption of CO2 from the air is the only factor involved in the hardening of the mortar. It is transformed into calcium carbonate (CaCO3) once the water has evaporated. Lime mortars are mainly composed of a mixture of aggregates (sands), binder (lime) and water in varying proportions depending on the intended use. The slaked lime (Ca (OH) 2), with the water acting as a catalyst, recombines with the carbon dioxide contained in the air, allowing the mixture to harden. This is what we use as a binder in construction. The quicklime (CaO) obtained by calcination is slaked by adding or spraying water (hydration), transforming itself into slaked lime (Ca (OH) 2). Depending on the composition of the original rock, the lime will develop specific physical qualities which will define its uses. Lime is obtained by burning (calcination) limestone (calcium carbonate – CaCO3). Indeed, lime mortars have two main advantages that cement mortars do not have: they are flexible and allow the walls to “breathe.” Until the beginning of the 20 th century, buildings have mostly been built using lime mortars, and generally, they hardly tolerate any intervention using current binders. Lime, in different forms, has been used in construction since antiquity (plaster or whitewash of ancient Greece, Roman mortars) however, lime has gradually been dethroned by Portland cement (which appeared in 1840), which became widespread during the 20 th century, even if its use should have been avoided in numerous applications. It is just a fine sand or aggregate with no bonding ability. It is, in reality, similar to limestone (Ca CO3), which has been crushed and is used essentially as a fertilizer. I’ll first briefly mention Agricultural Lime or “Ag Lime.” This is NOT a lime that can be used as a binder in construction. Which one should you select: Hydrated Lime, Hydraulic Lime, or Natural Hydraulic Lime? Why? How? The word “lime” encompasses a vast array of products, resulting in certain confusion when choosing the right product for the right application. Please continue reading to hear what Michel Couvreux, an industry leader, has to say, and remember to check out the good news about DISCOUNT PRICING at the bottom of the article. I truly believe it is the right material for pretty much any straw bale house however, I wanted to share with you the reasons why from an expert’s point of view. I have been using Natural Hydraulic Lime Plaster for years and am a huge fan of the material both in terms of workability and longevity. He also included input on the many confusing aspects of choosing and/or working with the right material for a straw bale house. I recently asked my friend Michel Couvreux of TransMineral, USA to write a guest piece about lime.
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