Tradical® EXTRAS…

1. The history of air lime: from its origins to our modern day

Air lime has been used for thousands of years by different civilisations and on every continent, with beautiful vestiges found in Syria, Egypt, China, India and Europe, to name but a few.

From ancient times through to the last centuries, lime was used in construction for all sorts of masonry, rendering and decorative finishes. Today, these creations remain an invaluable resource through their remarkable durability and beauty.

 

Lime comes from limestone, which is one of the most abundant minerals on the surface of our planet. Every region had its specific formula for using lime (depending on its culture, building systems, etc.), proving that lime could be adapted to different building projects — houses, circuses, arenas, theatres, bridges, aqueducts, spas, piping systems and so on — and meet the demands of specific uses.

 

Production methods did not change much right up to the 19th century. Despite traditional production methods being used over a long period, craftsmen used their expertise to develop specific procedures for producing high-quality materials.

 

The basic production method was always the same: limestone was heated in a wood-fuelled kiln over several days. The shape of the kiln evolved over time to enable better temperature control, the ideal temperature being 750°C. However, as these kilns were rather simply engineered, the results obtained from firing varied.

 

The importance of slaking

 

To compensate for these varying results which influenced the quality of the final product, this quicklime was always hydrated in a slaking tub. By immersing the quicklime in special pools, sedimentation would occur over several months to obtain the right quality and guarantee the consistency of the lime’s properties.

 

Lime breaks down in water and settles in different layers. Letting the paste mature enabled any firing inconsistencies to be eliminated by hydrating the dead burnt lime and giving under-burnt lime the time to sediment…

HIER. Ancien four pour la chaux aérienne sur le site de l'usine Balthazard et Cotte, Chaux du Périgord - groupe Lhoist
AUJOURD’HUI. Usine Carrières et Chaux Balthazard et Cotte. Four vertical pour la cuisson du calcaire
2. Producing air limes, hydraulic binders and cements

Binders for construction fall into one of two main product groups that differ in how they set: air products or hydraulic products.

The former require exposure to carbon dioxide in the air to set, whereas the latter set in water.

Hydraulic binders can be divided into two sub-groups: cements and hydraulic limes.

The production methods for these three binders differ greatly. Let us take an overall look at these methods.

Diagram of the complete production cycle, from extraction to the finished product

3. Why formulated limes?

Two requirements have led to the development of formulated limes: the need for faster setting times and for reducing operational costs. However, they also have to retain the essential qualities of pure air lime.

As they are prepared in an industrial environment, mix proportions are generally more precise than those obtained on a work site. But their production still draws on all the tradesman’s expertise.

 

Lime has been used since ancient times and there are still plenty of vestiges that can be admired and valued for their surprising durability. Different structures in Mesopotamia, Egypt, Greece and especially in countries ruled by the Roman Empire have been extensively analysed.

4. Lime and wall breathability

Vapour permeability and, more generally, moisture transfer are the trickiest problem for restoring old buildings. There are countless modern restoration techniques that fall short of the mark in treating this problem.

 

There are two reasons for this.

 

The first is that moisture transfer concerns the whole wall and can only take place in a continuum..

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