DESCRIPTION OF THE PROCESS
System intended to re-charge any cut stone element, with a material which physical and visual characteristics are identical to the material of origin.
It is a bi-component metal mortar which comes to replace the missing parts.
After hardening, the product is re-carved according to the traditional processes with the stone.
1.2. Field and limits of use
The nature of the metal mortars makes it possible to re-charge/ repair limestone (including the tufa and the chalk) or siliceous stones (including the sandstone) used in construction, in interior as in exterior, other than cold stones (marble...) as well as for the parts and elements containing lime or plaster binders .
It can also be used on hydraulic support or terracotta.
It can also be used in the rejointing of cut stone.
In case it must be poured/cast, the geometry of the parts must be compatible with its mechanical characteristics.
It can be used only for repairs whose smallest dimension (in particular the thickness) is above 10 mm/ 3/8 inch.
It can not be used on floor.
1.3. Constitution of the system
The metal mortar is a bi-component product :
· Metal powder.
· Metal liquid.
2.1. Choice of the metal mortar
According to the stone to be repaired, it is advisable initially to choose the most adapted metal powder.
This choice is done visually using control samples.
One chooses a metal powder:
· which grain is similar to that of the stone to re-load
· whose color is as close as possible to the color of the stone to repair but remaining lighter than the lightest of the parts to be re-coated.
· whose technical characteristics are as close as possible to those of the stone of origin (except in the case of the rejointing where one will choose a mortar more tender than that of the stone to be repaired: 2 mortars then will be used: one for the repairing, then the other, more tender, for the rejointing).
This choice must be validated by the building owner or his representative.
2.2. Preparation of the support
The stones must be purged of all their unhealthy or not adherent parts. They must be also cleaned of any possible layer (for example paint, stains or finishing mortar ), by scraping or scouring.
If the stone presents chalking ( crumbling), one proceeds initially to a remineralization with a silicic ester (Pétra Minéral).
The nosings must be leveled to obtain right and plain edges, if possible with an undercut. In particular, the refills ending in bevel of less than 1 cm / 3/8 inch thickness are excluded.
The supports must clean and be dusted.
In the case of refillings of more than 2 cm/ +3/4 inch thickness, one puts in place a pin, in brass. The pins will be connected between them by a brass wire.
It is advisable to protect the metal elements, aluminum, zinc or copper. In the event of projection on these elements, to clean with water.
2.3 Preparation of the mortar ingredients
One chooses the proportions of liquid and powder according to the hardness of the stone.
The following table summarizes the most current cases, but real tests will always be carried out, until one obtains the hardness of the stone of origin.
We draw the attention to the fact that the same building site can present stones of different hardness, according to the functions (the nosing of balconies are much harder than surfaces of stories) and according to the location (hardness generally decreases from bottom up to the top of the buildings).
It will be proceeded to as many dosages as there are types of stone.
Hardness can be created by the quantity of liquid put in the powder: the less one puts of liquid, the harder the stone is.
Type of stone
Speed of sound
Quantity of liquid for a kg of powder
500 g of liquid
450 g of liquid
350 g of liquid
320 g of liquid
One proceeds then to the tinting with the exact color of the stone to be repaired. One uses exclusively the same pigments as those used in manufacture. The setting with the color is made in “dry” by comparison in-situ with the stone to re-coat, while taking care to have homogeneous mixes.
2.3 Application of the mortar
Each stone is repaired separately. In particular, one must respect the joints and not weld the stones between them. The rejointing is carried out later on with an adapted product (for example Pétrus joint or Pétraline).
The support is moistened with metal liquid, except if the support is a stone with low porosity. In particular, the metal liquid should not form a film surface before application.
One mixes just the necessary quantity (cf table of proportion below), by pouring the metal liquid in the metal powder. One mixes immediately until obtaining a homogeneous mixture.
One applies the mortar as soon as this one reached a sufficient consistency, using a trowel. For applications in strong thickness, one charges by successive coatings without waiting time between them. For the thicknesses superior to 5 cm/ 2 inch., one applies a first layer of 5 cm, then a second layer as soon as stiffening and scraping of the surface of the first layer.
Then, as soon as stiffening (setting )of the last layer, using the trowel right away, one scrapes the surface off in order to open the capillary network.
For the use in rejointing, the implementation is identical.
2.4 Precautions for use
The metal mortar should not be used at a temperature lower than 5° C/ 41 F, nor in full sun exposure or under the rain.
Do not remix the mortar in the container, when its hardening/ setting has started.
2.5 Cutting of the mortar
When the mortar is sufficiently hard, one proceeds to the rejointing. One can then recut the product with a tool while following the traditional stone techniques according to the required aspect (strike off, chisel, sanding, etc…).
One dusts off after completion.
The complete drying of the product takes approximately a week. In the case of interior work, it is necessary to take care of a proper ventilation of the room.
It will not be carried out any work, nor surface treatments as long as the mortar is not perfectly dry. .