Restoration & HeritageReturn
Decorative elements using a template
This technique was used very widely in the 19th century for façade decoration. Indeed, the architectural styles of the period (neo-Classical, neo-Baroque, etc.) were rich in decorative elements. Moulding using templates of rectilinear elements – cornices, armrests, door and window frames, strips – became a standard. It replaced the traditional stucco style (lime, Italian pouzzalana and marble powder), which was very expensive for decorating buildings.
Using Prompt natural cement for template moulding means preparing a decorative mortar render on the walls of buildings that are made of ordinary bricks. For the mason this meant projecting fresh mortar onto a wall and immediately giving it the shape desired using a template, in the same way as ancient stucco work. Clever masons spread the mortar onto a part of the wall that that was sectioned off with struts or rules, and then used an ad hoc profile template. This process was perfect for smoothing cornices or any other rectilinear elements. The mason was therefore able to apply a mould, and give a more complex form to the moulding, or sometimes create a sculpture by cutting original parts into the fresh mortar.
Used on its own with the retardant additive Tempo, or mixed with natural lime, Prompt natural cement is used in mortar. Its thixotropy, its finesse and its adhesive qualities allow mouldings to be applied perfectly. Furthermore, the speed of execution allows mouldings of between 2 and 15 cm thickness to be completed in several passes in the same day. Numerous buildings in England benefited from the advantages of its lesser cost from the beginning of the 19th century.
Mouldings and thick cornices are frequently used on breeze blocks or bricks. These relief elements are sometimes no longer in place. In the case of substantial loading, it is crucial to use a resurfacing fixing structure comprised of brass or glass fibre dowel assemblies, and a light frame using the same materials.
Suggested doses for Prompt natural cement only mortar (in volumes):
The mix must be weak to obtain a level of porosity allowing good transfer of humidity.
Making template mouldings suggests the use of different mortars, as in the mixing of rendering. The aggregates used will be progressively thinner from the heart of the moulding through to the finishing coat. A final stucco pass (mortar made up of Prompt natural cement and a very fine aggregate such as marble powder) can be completed immediately after the finishing coat (a fresco).
Preparation of the surface: It is important to clean and dampen the surface properly. Then, apply a grout of Prompt natural cement using a brush on the damp brick. Allow this coat to harden, but not completely.
The core of the moulding: Prepare a 1:2 sand mortar (0–4 mm) using a retarding agent: 0.25 to 0.5 capfuls of Tempo per litre of Prompt natural cement (according to temperature). Cast the mortar using a trowel. The template must be passed over several times, so as to eliminate any excess material. Once the previous layer has lost its workability through surface absorption, before it has started to set, apply an additional coat.
Exterior finishing coat: Prepare a 1:2 fine sand mortar (0–1 mm), adding a retarding agent: 0 to 0.5 capfuls of Tempo per litre of Prompt natural cement (according to temperature). The mortar must be very plastic, with a view to aiding extrusion. Then, cast this using the trowel and wait the necessary time before passing the template over it, i.e., between the loss of workability and before the onset of setting. Then apply another coat.
Fine exterior colouring coat: Prepare a 1:1 fine sand mortar (0–1 mm) with pigment or 1:1 marble powder with retarding agent: 0 to 0.5 capful per litre of Prompt natural cement (according to temperature).
The mortar must be of liquid consistency so as to accurately mould the fine edges. It will be cast or applied with a brush and then the template passed over it several times. Repeat this operation until a perfect finish is achieved.
For good bonding, it is preferable to work wet-on-wet. The surface must be damp before removing the template. Small amounts of mix should be prepared, so that they an be applied in time. Two workers can coordinate, one mixing the cement and another passing the template. It is important to pass the template over when the mortar is starting to lose its workability. As the template is being passed over, the surface of the mortar must be properly lubricated with sprayed water. The key to success is to pass the template over during the right phase of hardening of the previous coat.