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Particularly exposed to bad weather, the stones of an external staircase take over time an incomparable patina. But it can hide damaging damage (cracks, degraded joints, molds...) that give the signal for intervention without delay.

Renovate a stone exterior staircase

In local stone, an external staircase attached to a masonry wall is slowly deteriorating. A quick examination reveals marbled stains, degraded joints under the combined effects of ground movements, rainwater and sun! A cost-effective and simple-to-implement remedy avoids the threat of complete degradation if things are left as they are.

The preparation

At the risk of repetition but repairs can only be made on healthy, clean and dry surfaces. The pressure washer is the essential material that will eliminate as much dirt, mosses and expose the damage they concealed!
● Cut and tear vegetation that cannibalizes the masonry. Burn with a soldering lamp the roots anchored in the joints. Cleaning starts at low pressure to prevent the jet from causing further damage to the joints. If it is not enough to remove stains, add a specific fungicide or detergent treatment product to the pressure washer.
● With the end of a cat tongue trowel, a chisel... probe the joints. Test the strength of the mortar but without exaggerating the leverage or punching effort. Otherwise, all the joints will have to be redone. Dig those that are defective for at least 2 cm.
● The holes left by unsealed stones are cleaned and scraped thoroughly. The cracks are widened and carved with a chisel or grinder if necessary. The friable and non-adherent parts are removed by scraping, brushing... with a water jet or possibly with a high-pressure cleaner.

The repairs

To repair stone joints or replace a stone, a lime mortar or bastard is preferable to a cement mortar. based on NHL lime, it remains flexible over time, protects against bad weather and offers good permeability to water vapor. It can be mixed ("bastardized") with cement to shorten the drying time and increase the resistance of grouting.
● Mixed with a 35 kg bag for 90 l of sand and 20 l of water, the lime is chosen according to its resistance class and the hardness of the stones: NHL 2 on very soft stones and NHL 3,5 on soft stones. On the latter, a bastard mortar (50% of cement and 50% of lime) or a bastard lime ready to spoil (NHL-Z) is also possible ("Calix" or "Renocal" of Calcia, "white lime" of Lafarge cement...).
● On hard stones, a resistant mortar is required. It is essentially bastard mortar to make or lime ("Tradifarge" Lafarge Cement) or masonry cements ("Multibat" Lafarge Cement, "Baticem" Calcia...).
● To seal a stone, fill three quarters of the mortar cavity. Place a stone of a suitable size. Push to push back the mortar on the sides and wedge. Let shoot before making the joints.

Clean the steps

Clean the steps

Remove the mosses, lichens, dirt and vegetation embedded in the steps and the base of the walls with a pressure washer, set on low pressure so as not to damage the joints too much.

Remove vegetation

Remove vegetation

Tear off the vegetation that resisted the pressure washer. The soldering lamp is an effective way to eradicate roots anchored in joints or placed in hard to reach places.

Widen cracks and dig joints

Widen cracks and dig joints

Expand cracks and cavities left by loosened stones to facilitate penetration of the mortar. Dig joints that are damaged, friable or no longer adhere to a minimum depth of 2 cm.

Grinding

Grinding

Use a "one-handed" angle grinder, equipped with a diamond disc preferably, to widen and deepen the cracks in the hard stone. It is a saving of time and fatigue very appreciable.

Prepare the mortar

Prepare the mortar

Prepare the mortar respecting the cement-lime-sand and water dosage. It must be bold and supple, neither too dry nor too wet. A pre-prepared mortar, ready to waste, can be used for small quenchings.

Seal the missing stones

Seal the missing stones

Moisten the support. Start by sealing the missing stones. Place a thick mortar bed in the cavity. Place and wedge the stone by aligning its facing side with the masonry. Let shoot.

Fill with mortar

Fill with mortar

Fill the hollow of the joints and those of the resealed stones by pushing it with the edge of the trowel. Stuff until refusal and allow to pull before smoothing the mortar with the flat end of the blade.

Seal

Seal

On the stone steps, posed touching one another, sealing is done with a butyl putty for cover. On cracks, an acrylic sealant for masonry or polyurethane is more appropriate.


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