Grouting of an old natural stone wall

Grouting of an old natural stone wall

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In the basement or on a whole section of the wall, it is sometimes pleasant to find the original stone and keep it as natural as possible. In order for this type of wall to be compatible with routine maintenance, it is often essential to joint it. Forget the raw cement from the 1970s and make a bastard mortar whose color will be close to that of stone.

Before you start

With a chisel and a mallet, completely strip the surface of the wall of any residue of plaster or mortar. If the joints crumble, do not hesitate to dig them with a chisel. For perfect cleanliness, brush your stones with a wire brush.

Preparing the mortar

In a plastic trough, mix 10 parts of fine sand for 3 parts of lime and 2 parts of white cement ... You can vary the proportion of lime, while respecting the final dosage. Experiment with small quantities to check the shade obtained. Indeed, the color of the sand is essential if you want to get as close as possible to the color of the stones ... It is not excluded to add a hint of natural pigment to tint your mortar, it's all a matter of taste. To reinforce the qualities of the mortar, you can also add an adjuvant to it: a liquid resin which strengthens its resistance to shocks (particularly interesting property in the lower part), a liquid hardener which will further limit dust…

How to do ?

Carefully mix the sand and the binder (lime and cement), make a central well, then add very clean water. Intimately mix the water with the sand and the binder to obtain a homogeneous, unctuous and flexible paste which is firm enough to hold on your trowel ... It is all a question of dosage. The opening time, i.e. the time during which you can use the mortar before it sets, is about half an hour. To avoid having to work in an emergency, prepare small quantities of mortar ... And take care to note the proportions to find your "formula" throughout the work!

The step by step



Generously dampen your wall and always start at the top.


On your float, place a dose of mortar. Approach the trowel with the wall, take a little mortar with the trowel and introduce it into the joints. Depending on the finish chosen, these joints will be flush with the bare stone, protruding if they protrude a little, or recessed if they are packed with a joint iron.


One of the stones is gone? Here is a simple technique to replace it. Choose a stone slightly larger than the part to be filled, then use a hammer or stubborn, whose sharp part is cut in bevel. Starting from an edge of the stone, cut it in small steps up to about two thirds of this face; then turn the rubble over to attack the remaining third and thus obtain a perfectly flat side. Place your bastard mortar in the hole, moisten the stone and install it in its housing by forcing it in with the hammer part of the stubborn. Know-how - home decor © La maison rustique - éditions Flammarion, 2006