Michael Gaisford

Basically, there are two types are lime.

In French; Chaux Hydraulique and Chaux Aerienne. These limes are used in two different situations and it’s important to realize their differences.

Chaux Hydraulique is used in the undercoat layer when using lime in a render. When lime is mixed with Hemp (Chanvre), Chaux Hydraulique is used in this insulative layer. The properties of this lime make it suitable as it absorbs moisture from the atmosphere when the air is damp, and gives it back into the atmophere when the air is dry. This property means that the conditions inside a house where this lime render is used, are more constant. This phenonomen is known as a house which ‘breathes’.

Chaux Aerienne is the lime used in the top coat. When this lime is mixed with Hemp it produces a fairly hard surface which resists wear. The lime will still allow moisture to pass through it but it does not absorb moisture like Hydaulic Lime. Consequently, this top coat acts more like a plastered wall and can be wiped clean without damaging it.

The two common types of lime which I use are:

1. Chaux Hydraulique;

Chaux de St Astier, NHL 3.5.

(Be careful as you can find sacks of lime which are marked similarly, NHL 3.5 Z , but this is a lime that also contains cement!!! ……not so good if you want a lime to breathe! )

2. Chaux Aerienne;

Batidol.

Usually, if you are not sure about which lime to buy, there will be someone at the suppliers who understands the differences ….. but not always.!!

So before choosing the lime you will use it is necessary to understand the job it will do.

Generally, ‘builders lime’ (Chaux blanche) contains cement and it is that which is used for pointing, and general building use. Just because it is used by builders does not mean that it is the best choice. If you are trying to build a home which breathes and is kind to the environment it is best to use pure lime.