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Slate is a tough material but it breaks down over time due to frost and shocks. Loose slabs and chipped noses can be repaired and give new life to a staircase.

Text and Photos C. Petitjean

Practical advice

To be strong and durable, the setting of the mortar must be slow. The backing of the coating is wet, as well as the slab that you soak for a few minutes in a bucket of water before laying - especially if it is hot -. If the parts to be coated are small and prone to stress (stair nosing), apply a bonding resin ("Trapco latex" by Weber and Broutin or "Sikalatex" from Sika) to the substrate before the mortar. sealing. The preparation is one volume of product for two volumes of water.

Slate is no longer limited to roofing. It is used both inside and outside paving (courtyard, terrace...). The steps of the staircase presented here are covered with slabs of unpolished black slate, about 1 cm thick. Their rough and irregular appearance harmonizes with the stone and is found on the floor of the outdoor courtyard. Joined with cement mortar, some slabs were peeled off because of frost. Only the stair noses received a straight cut. Damaged by time and incessant shocks, some are to be replaced.

Prepare the support

The work begins with a stitching of the old laying mortar. It is done with a hammer chisel equipped with a sharp chisel. Failing this tooling, pointerolle mason and hammer are enough.
● When approaching the riser, be sure to moderate blows to prevent masonry from bursting. The surface is then brushed and dusted.

Take off the slates

To prepare the laying mortar, dry mix in a trough a lime and cement product ("Multibat" from Lafarge or "Baticem" from Ciment Calcia). Pour water until you have a smooth mixture. The flexibility of the lime combined with the cement reduces the risk of cracking.
● Moisten the surface of the step to be repaired with a sprayer. Lay the mortar with a trowel. Next, lay the slate slab "crushing" the binder bed, then pat it with a rubber mallet to get the correct positioning. To achieve a good alignment of the stair nose, use a guide bracket.
● After drying for a few hours, grout by grinding the mortar with a cat-tongue trowel. Brush with a broom and clean with a damp sponge.

Adjust the walking nose

Natural slate is a material that tends to flake, crack (cleave) under impact. To replace the damaged element, cut the replacement part to the chainsaw in a slate in good condition.
● If you can not get the same material, one trick is to draw a line on the slab, parallel to the damaged edge. Cut the degraded part to the diamond disc, loosen the joints at the ends and gently lift the plate to the flat chisel by leveraging. Turn the piece over, the cut-out section presented at the front to get a clean, straight edge. Fixing mortar is as before.

Remove the damaged slab

Remove the damaged slab

Slab laying starts with the preparation of the support. Pick hammer hammer but stop about 2 cm from the riser so as not to burst the front face.

Fix and upgrade a support

Fix and upgrade a support

Cut a piece of liteau straight on which will rest the slab to seal. Leveled, it is held by a small corner of wood wedged between one of its ends and the wall.

Spread and squeeze the mortar

Spread and squeeze the mortar

After moistening the masonry support with the sprayer, spread out and press the groutless mortar with a trowel. It is dosed on the one hand with lime-cement for two parts of sand.

Lay the slabs

Lay the slabs

Press the new slabs onto the mortar bed. Maintain the alignment by placing an aluminum ruler on the stair nosing. Then tap the slates with a mallet to adhere.

Pull the mortar and clean

Pull the mortar and clean

Finish by tamping mortar into existing wide joints. As soon as he has "pulled", brush the tiles with a brush and wipe off the dirt with a damp sponge.

Repair a walking nose

Repair a walking nose

If a step nose is chipped: draw a dash in the middle of the slab then make a straight cut with a chain saw with a diamond disc. Peel off the front with a flat chisel.

Strengthen the seal

Strengthen the seal

To reinforce the sealing of the small slate strip: first apply (with a brush) a primer to the substrate or mix it with the mortar, without adding water.

Slab, seal and cleaning

Slab, seal and cleaning

The mortar bed spread on the support, position the slate slab, cut side forward: thus the walking nose is clear. Fill in the joints. Clean with a coconut brush.


Video Instruction: How to Clad Concrete Steps in Stone - This Old House