- Stripping the stone
- Repair fragments and chips
- Reconstitute a stone angle
- Make a piece of stucco cornice
In spite of its reputation, the stone is not eternal, especially when it is a limestone, exposed to the aggressions of a polluted atmosphere.
It is not a question here of restoring the arm of a statue, or the granite arch of a porch, but of repairing a break on a cornice or of giving back to the mantel of a chimney its old appearance.
Stripping the stone
As it is difficult to accurately assess the extent of possible damage under dirt, moss and lichen, any renovation operation necessarily begins with a general stripping of the object or the damaged item.
Cleaning the stone
It is a more delicate operation than one generally imagines, because it must be adapted to each type of stone.
Be very careful before attacking the stone exposed to bad weatherand especially acid rain, which transforms calcium carbonate (the basic constituent of calcareous stones) into calcium sulphate, that is to say into friable plaster.
- Mechanical brushing with a rotating wire brush, is to proscribe on all the limestones.
- A small rotating brush made of nylon thread however, it can be used to remove small patterns or de-ditch the bottom of grooves on a cornice.
- The pressure washer is effective at removing a layer of mosses and lichens:
- do not use the rotating nozzle which may irreparably dig the stone;
- use a spatula or a chewing knife to take off the lichens in the bottom of the reliefs.
The plaster of plaster
It is a very popular way for professionals in the restoration of sculptures, bas-reliefs and statues. This is the best way to obtain the complete removal of a stone object: it avoids as much as possible the risk of attacking the sick parties.
- Pour demineralized water in a large plastic container, and dissolve 50 g of ammonium carbonate per liter.
- Saturate the paper pulp mixture to have a homogeneous paste. This pulp is obtained by soaking, always in demineralized water, plain white paper (never printed paper).
- Apply this paste (handle with gloves) on the stone to be stripped and let it dry.
- Eliminate the dry pulp with quack grass brush.
- Rinse abundantly under pressure.
Repair fragments and chips
Aggressions of time and men cause damage and sometimes damage the stone, or eliminate some details of a carved part. In some cases, the stone becomes friable. It is then necessary to intervene to restore the work, taking care never to disfigure it by a too visible repair. It should never be a question of making a restoration "to nine" anachronistic and always very visible. The patina of time must be respected, because it participates in the charm of the old.
Synthetic resins, added to single-component repair mortars, ready for use, are very practical for the simplest repairs. Wear rubber gloves to handle these products that may cause skin allergies, even burns.
It is widely used by specialists to restore details on limestone statues. The lime flower (air lime extinguished) is the base of this mortar, added sieved sand, dyestuffs, marble powder and, for objects exposed outside, water-repellent resins.
Reconstitute a stone angle
1. Prepare the filler and color it to give it the hue of the stone to restore.
2. Mold a sheet of folded paper on the corner and let cure 24 hours.
3. Apply the product on both sides of the corner, with a coating knife.
Make a piece of stucco cornice
1. Using a talcated metal cylinder, make a strip of modeling clay 2 to 3 cm thick and mold it on the part to be redone.
2. Unmold the modeling clay and place this shape in a box filled with sand that will prevent it from deforming, the two edges horizontal.
3. Pour some modeling plaster up to about halfway up the mold, then arm the piece with hemp fiber.
4. Fill the mold completely and place some hemp threads in the edges of the widest part.
5. After drying (12 to 16 h), unmold and re-cut the piece so that it fits into the part to be redone. Glue it in place using a putty-glue, remove the excess and sand after drying.
(photos / visuals: © DIY_Prod, except special mention)
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