5.    Sunken batten decorations in plaster on facades

Stucco, ashlar and imitated/artificial stone on facades can be made in several ways, but the sunken b atten technique, which is described here, is definitely the masons work, while the technique of making ashlar with running moulds is mainly carried out by the stucco workers - sometimes by the masons. 
Sunken batten decorations is made of specially formed battens, which make an imprint in the wet mortar, and by this, when the battens are removed again, imitating pointings or forming edges of natural stone work. 

Drawing no.8 shows the different varieties of relief imprint decorations. Most common are ashlar decorations, but also other possibilities are indicated. Ashlar can have various appearances, as shown on drawing no.11, both regarding the relief in the pointing grooves and the character and structure of the surface.

Tools and utensils

The various tools, both for carrying out the ashlars and for the surface treatment, are shown on drawings no. 9 and 10. 

Materials
The materials are hydraulic lime mortar and on buildings after 1860 often Portland cement mortar. To day we recommend hydraulic lime mortar (1:2:9) both for making new ashlars and for the repair of old decorations, because the old remaining cement materials are now so weakened that insertions with new, modern cement mortar will cause problems.

Making sunken batten decorations

The backing coat for the sunken batten plaster decoration has to be 2 layers of rough mortar, thrown on well watered masonry, smoothened and after this hardened for 2-3 days or a whole week.
A lot of battens are planed to obtain the right shape for the revers imprint of the pointing grooves. After this the fillets are soaked, totally sunken in water for a couple of days. The shrinkage of the wooden battens after the hardening of the mortar and the drying of the wood makes it possible to remove the battens again without spoiling the edges of the pointings. Besides this the battens must have a conical and chamfer shape. 
When the backing is ready, the battens are placed and fixed to the facade, in the wished pattern (Drawing no. 10). After a thorough watering of the backing coat, a layer of rough hydraulic lime mortar is thrown on the surface and smoothened, approximately 1 cm under the outer level of the battens. 
After a weeks hardening the ground is thoroughly watered and a finishing layer of fine grained (0-4 mm sand) hydraulic lime mortar is thrown on. Now the surface is smoothened and glazed very carefully, to the same level as the outer level of the battens. 
While the mortar still is wet, and the battens still at its place, the desired surface structure is carried out, except the stone carved surface (no. 5).
After a weeks hardening the wooden skeleton is removed very carefully, in order not to destroy the edges of the pointing profiles. The screw holes, possible missing parts or air holes are repaired immediately, if necessary with special shaped jointer. 

Surfaces structures on ashlars

1 Glazed or polished surfaces are made by a smooth wooden float and a metal board
2 Splatter dashed surfaces are made of a relatively rough lime mortar, thrown on the surface through a rough sieve. In order to appear as natural as possible, the mortar ought not be adjusted after the application.
3 Sparrow picked or combed/brushed surfaces are made with special tools as shown at the drawing, while the surface mortar is still wet. The comb or besom is often draw slantingly. 
4 Granite gravel surfaces are made of selected granite gravel, either rough cut and sharp rubble or small round gravel, which is thrown at the wet mortar or pressed or pushed in place. To fix the gravel, it is furthermore pressed in the ground by a roll or a wooden beater. 
5 Rough carved surfaces are made by leaving the surface 2-3 cm higher than normal. After one week of hardening the surface is carved with stone carving tools: Flat chisel, tooth chisel, point chisel, flat hoe and tooth hoe, for different surfaces.

Lintel-constructions

The lintel-constructions is an important element of ashlar decorations on facades in connection with holes for windows and doors. The lintel can be horizontal or curved/bowed.
In the first place it is important that the horizontal lintels are not made totally straight, but constructed with a very small bow upwards, only 1 cm, because if not, they will seem to be "hanging".
Secondly, when imitating stone work, it is necessary to think and to "copy" how a stone mason would construct the same detail in real stone. To be able to receive the pressure from he load, the corner stones are cut without sharp edges, which tend to break off. Therefore the upper edge of the window- and door holes are often raised or lowered approximately 5 cm in proportion to the horizontal joints - to prevent sharp and therefore weak edges at the particularly loaded bedding stones in the upper corners.

This gives some varieties in the design, depending of the hight of the lintel stones as shown on drawing no. 13. 
If an existing ashlar does not have these details, it must not be changed, but kept exactly as it is now. Many lintels on existing old buildings are made in level with the horizontal joints. But the right way to construct this detail is to imitate, not only the external likeness, but also the stonemasons craftsmanship and natural and functional constructions.

Index