Restoring ancient masonry (first half of the twentieth century and before) aims to make them effective in their protective role and the beauty and quality of the original textures. For this purpose, mortars for joints and coatings will be able to limit the risk of cracking and will have a good water repellent effect against rainwater while allowing the walls to breathe. Air lime, enriched with hydraulic binder and specific components in suitable proportions, will therefore be preferred as the base of these mortars. The use of mineral pigments and regional sands adds to the means to respect, enhance and embellish these masonry in their environment.
- Stainless trowel
- Knife to coat
- Rule (smooth, notched)
- Cement mixer
- Taloche (honeycombed plastic)
- Taloche (wood or sponge)
- Builder's broom
- Gratton (short teeth, long teeth)
- Presentation and mortar for regular support
- Mortar for disparate support
- Trowel finishes
Presentation and mortar for regular support
1. In the past, masonry was mounted and coated with mortars of varying composition (earth, clay, straw, aerated lime, sand...). They are therefore generally quite friable and not very resistant especially after the passage of time.
2. After checking that it is not a plaster mortar or plaster-lime, remove all old plaster. Remove the joints by 2 to 5 cm on the hammer according to the texture of the material in order to promote the attachment of the renovation solution, joint or coating.
3. The use of traditional mortars must meet two basic principles: the "tri-layer" system and the degressivity rule for binders, which are included in the rules of the art (NF P 15-201 / DTU 26- 1). Two cases can arise: a regular support, presenting the same material or a support composed of disparate materials, consequence of various previous reparation interventions. In the first case, the "gobetis" (1), layer of attachment of the support, is thrown by trowel or projected directly on the support and must also fill the joints that have been dug. Its thickness on the support is about 3 mm.
4. The "plaster body" (2), once erected, ensures the flatness of the support and with the gobetis, it ensures the protection of the support against the rain. Its thickness can vary from 15 to 20 mm.
5. The last layer of plaster, "siding", is the one that will be visible. It is she who will receive the rain but will also suffer sun and frost. It must therefore present the qualities accordingly. Finally this layer will be the ornament of the facade. It will be necessary that the decoration that it will present (colored coating or paint) respects the former aspect that proposed the building before its restoration.
Mortar for disparate support
6. In the case of a support composed of disparate materials, it will be necessary to drop what does not hold then to clean the masonry with the jet of water. Then unroll galvanized wire by fixing it on the support with jumpers also treated against corrosion.
7. Make a gobetis with a coating specifically prepared for this type of work, on the parts of the wire mesh as on the parts left bare. But in case of wall with unevenness, it may require a slightly larger thickness. Let dry 48 hours.
8. In the same system and after surface drying of the gobetis, continue to make the plaster body then scrape its surface with a road broom. Streaks caused on the coating still fresh, will facilitate the attachment of the finishing plaster. Let cure 7 days minimum.
9. Depending on the desired finish of the facing layer, use plaster for specific finishes: For local sand use a colored aerial lime binder.
10. To continue to a trowel finish, lay the layer of plaster to the notched ruler to obtain a thickness of 5 to 7 mm and then pass the knife to plaster.To continue to a scraped finish, lay the plaster coat to the smooth ruler to obtain an average thickness of 10 mm then pass the knife to coat.
11. To finish a trowel finish, go to the plaster, as soon as it has the right consistency, (let it a little pull), a trowel plastic honeycomb or wood. The sponge float is possible provided you have mastered the technique.To finish a scraped finish, go over the coating as soon as it has the right consistency (surface more drained than for the trowel finish), the tool appropriate (gratton with short or long teeth, depending on the desired grain).
(photos / visuals: © Weber and Broutin, except special mention)
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