Introduction – Why use lime?
According to the experts, because tuffeau is a highly porous stone only lime based materials should be used on it. The lime allows the stones to 'breathe' and therefore not trap water.
Covering tuffeau in concrete or emulsion paint traps moisture within the stone which can lead to it deteriorating and eventually crumbling away.
Safety!
Lime is corrosive and can burn soft tissue so wearing safety goggles and gloves is advisable. Actually, if you don't want to risk your eyes being damaged irreparably then close fitting goggles are an absolute must.
When mixing the mortar it is also advisable to wear a mask in order to prevent inhalation of the powdered lime.
Wall Preparation
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| Cleaned tuffeau wall |
Preparation is everything. Depending on the thickness and hardness of the material covering the stone you can use a toothbrush, paint scraper, hammer and chisel or other suitable implement to gently prise the covering away from the stone. Normally Mr Riotlife uses a hammer and chisel for the large areas while I follow behind with a paint scraper and toothbrush to take off the smaller and more difficult to get at areas.
WARNING – tuffeau is a very soft stone and marks easily.
Finally, using a soft brush, remove any loose mortar, tuffeau and debris from the surface of the wall and then use a screwdriver or other flat bladed tool to gently remove any loose old mortar from the joints.
Mortar - the mix
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| Lime mortar mix |
After much research and lots of trial and error we think we now have the perfect lime mortar mix for our walls. Using chaux aerienne we currently work on a ratio of 1 part lime, 3 parts sand, 1 part powdered tuffeau and 1 part water.
The result is a pale, almost creamy white, slightly rough mortar that blends well with the original mortar. As repointing is a painstakingly slow job the makes the shoulders and wrist ache I mix only a small amount of mortar at a time in order to make sure it does not dry out before I use it. To help make a small amount I use a 420ml (15oz) tomato tin as a measure.
Mortar – application
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| Spraying joints with water |
The key to making the mortar stick to the wall is ensuring the surface it is being applied to is wet, not just damp. The joints to be repointed should be sprayed until they are glistening but not quite dripping wet - this is a surprisingly large amount of water.
Using a pointing trowel (truelle longue de chat if you buy one in France) work the mortar into the joints.
Then, with the back of the trowel gently smooth the surface of the joint so that it is level with the stone. However, if your stone is as uneven as ours you will need to just choose a level that is pleasing to the eye.
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| Repointing tuffeau stone wall with lime mortar |
Mortar – drying
You think that after all this, your work is done. Unfortunately, lime mortar can take many weeks to cure properly during which time it is imperative that it does not dry too quickly. If the temperature is high, gently spray the surface of the mortar with water to slow its drying.
Conclusion
Lime mortar is the perfect material for old soft walls, and we have done our best here to give you guidance on how to make and apply it.
However, when you come to use it, just make a small quantity and practise with it before you embark on a large piece.
