Old masonry is often wet and salty, especially in areas known for their humidity and may suffer from a lack of sunshine. In addition, the east and north orientations accentuate this phenomenon. To find healthy masonry, it is advisable to use a mortar adapted to this type of pathology after having completely cleared the walls of old coatings by a complete picket.
- Cement mixer
- Mortar pump
- Projection pot
- Honeycombed plastic float
- Garden hose
- Schemes of old masonry subject to capillary rise
- Restore a masonry by making a Gobetis
Schemes of old masonry subject to capillary rise
1. Old masonry rarely shows capillary breaks (bituminous textiles, slates...). They are therefore subject to capillary rise, frequently loaded with salts (carbonates, sulphates, nitrates or others).
2. As the seasons go by, the level of rise in humidity varies. In the zone of variation (H-h), the water evaporates, traces of humidity appear and the salts are deposited on the surface. In contact with bacteria, some salts become saltpetre.
3. As the years go by, salts accumulate inside the wall and the plaster. In contact with moisture, this large quantity of salts swells, swells and breaks the coating.
4. To eliminate the appearance of moisture and saltpeter stains on the surface of the plaster, a large network of channels must be created inside the plaster to facilitate the flow and rapid evaporation of the plaster. 'water.
5. In order to prevent the plaster from bursting, it is necessary to create reservoirs inside the sub-plaster which make it possible to store the salts and to support their expansion.
6. In order to maintain the operation of the two preceding principles, the chosen decorative plaster must also allow gaseous exchanges of the sub-plaster with the atmosphere: a coating based on aerial lime is suitable for this use.
Restore a masonry by making a Gobetis
1. Remove all existing coatings as well as mosses, lichens and other pollutants. Then remove the masonry joints 2 to 5 cm deep and remove the dust by washing with a jet of water.
2. In all cases, replace the missing stones or bricks with new ones of the same type and quality by sealing them with a suitable coating.
3. On hard stones and little absorbent, make a gobetis adjuvented with a specific product of attachment. On very porous bricks or on the contrary vitrified, on soft stones or on heterogeneous masonry, fix a galvanized wire which will be used to hang on the gobetis.
4. Make a gobetis 3 to 5 mm thick. Fill the masonry joints and cover each jointed area with a 5 mm thick plaster board beyond the bare stones. Roughly rule: the surface of the coating must remain rough to promote the hooking of the finishing pass. Allow to dry for a minimum of 12 hours.
5. If you have a mortar pump (for rent, for example), fill the joints of the masonry with a special mechanical splashing product and then cover each grouted area with a 5 mm thick plaster run. beyond the bare stones. Roughly rule: the surface of the coating must remain rough to promote the hooking of the finishing pass. Allow to dry for a minimum of 12 hours.
6. Apply and erect a weber.mep SP pass with a minimum thickness of 20 mm and a maximum of 30 mm in all areas, at all points, in bare stones. Leave on the surface, a rough enough state to facilitate the attachment of the topcoat made with a coating based on aerial lime.
7. The restoration of these walls, exposed to the east and north, was conducted by taking again the traditional system of a coating with 3 layers (gobetis and body of plaster, special to prevent the stagnation of the humidity + the final rendering coating, based on lime air to let the support breathe). This work allowed to give back to this same house, all the charm and the clarity of a welcoming facade.
(photos / visuals: © Weber and Broutin, except special mention)
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