6.  Running mould decorations in plaster on facades

The main cornices, the architrave and horizontal friezes, the window- and door casings and possible half columns are typically made by running mould. But also ashlars can be constructed this way.

Materials
Running mould decorations on facades are constructed of air lime mortar or hydraulic lime mortar. After 1860 also Portland cement mortar is used.
To day we recommend the use of air lime mortar (1:3) or hydraulic lime mortar (1:1:6 or 2:1:9) both for making new Running mould decorations and for the repair of old decorations, even if they are originally made of cement. The old remaining cement materials are right now so weakened that insertions with new, modern cement mortar is not appropriate.

Tools and utensils
Running mould are made by a sheet zinc mould, mounted on a wooden sledge, which is able to ìRunningî or glide along the facade, via horizontal or vertical rails and guides, fixed to the facade. Furthermore special trowels and boards are necessary.

Making Running mould main cornices and friezes
At first it is necessary to make an exact drawing 1:1 of the profile or mould of the cornice or frieze. If an existing cornice is repaired or replaced, the old and original profile must be painstakingly measured and recorded - on a place, where the profile is most best preserved and correct. 
To verify the exact shape, a accurate templet is made in paperboard, and tested and corrected at  the spot. Note that the main cornice are often made with a little oblique drip (under carved) internally, to prevent water drops from "hanging". This must be carefully copied. 

It is on the other hand quite important, that the running mould decorations, especially the main cornices, have good proportions, so in glaring cases, it is allowed to improve the shape. 
The next step is to make a accurate sheet zinc mould of the same shape as the cardboard templet. After this a 1 cm smaller sheet zinc mould is made for the first, muffle running mould. Both sheet zinc moulds are nailed to a piece of board or plywood, cut out 2-3 mm smaller than the sheet zinc mould, and provided with a chamfer towards the profile.
The wooden piece with the sheet zinc mould is now firmly mounted to a wooden sledge with a special lock wedge and two shore lists, fixed with screws.

Now two wooden rules are mounted at the masonry, following the future lines of the cornice, frieze or casing, at the facade, and adjusted in proportion to the right height and course of the running mould sledge. As the mortar layer must not be more than 5 - 6 cm thick, all larger running mould decorations must have adequate corbellings of bricks or stone in the masonry. Therefor it is necessary to test the running mould sledge at the spot, in order to ensure, that the applied mortar layer everywhere will be between 3 - 5 cm thick 
After plentiful pre-watering of the backing, coarse hydraulic mortar is thrown on, and the small sized reverse running mould drawn with the slanting edge pointing backwards. This is done several times, until the shape is complete, according to the small mould. If the surface is very smooth, it will be necessary to scratch small grooves in it.
After 2 - 3 days of hardening, preferably more, we are ready for the finishing coat. The mortar for this must be made with air lime, wet slaked for at least 3 years, mixed with very fine sand (0-4 mm), in proportion 1:3. Mixing time: 20 minutes.
The ground is pre-watered and the fine grained mortar thrown on and treated with the larger reverse running mould mounted at the sledge. When the shape is completed, a finish coat is applied, mixed in the proportion, lime sand 1:2, while at the same time, the running mould is drawn the opposite way -  with the slanting edge pointing forward. This creates a particular hard, smooth and weatherproof surface.

Photoserie I: Making running mould friezes

A Setting up the wooden roles on the masonry
B Testing the reverse zinc mould for the space for the corbellings
C Coarse mortar is thrown on
D The running mould scrapes surplus mortar off
E  Fine mortar is thrown on
F The running mould scrapes surplus mortar off and smoothens the surface
G Detail of the running mould
H Detail of the running mould
I  Detail of the running mould

It will often be necessary to make the last 10 cm at the end of the running mould decoration ìby handî, as the sledge has only a certain length. This is done with a collection of special wooden floats - never with a sponge, as this will damage the edges and spoil the lines.
The reason why the running mould decorations are made in two separate operations - with two sheet zinc reverse moulds of different size, is to prevent the small shrinking cracks in the surface, which inevitably will occur if thicker layer of mortar is applied continuously  "wet-in-wet". By laying a relatively thin finishing coat on a thicker, but hardened ground layer, the shrinking cracks in this will be filled, covered and minimized. As these cracks, even if they are quite small, often causes increased deterioration and approaching damages, especially on  decorations exposed to rain, this more complicated procedure is absolute worth while. 
Running mould decorations are sometimes pre-fabricated at the workshop, cut in suitable elements, transported to the building site and mounted here like the cast decorations. 

Making curved running mould decorations 

Door- and window casings are sometimes curved, which is also possible to make with the running mould technique as shown on drawing no. 17. 
The straight parts are made with a smaller running mould sledge, thus enabling the mould better to reach the often sharp bottoms. To make the curved parts, the sledge is mounted on a special board, fastened at the constructed centre for the curve, arch or chord - sometimes more than one centre is necessary. The centre point is fixed with special arrangements. 
Another method is to set up specially curved rules - and draw the running mould along these. They can describe any possible curved form. 
Other curved ornaments on facades made by running moulds

A lot of other curved ornaments on facades could be made with the running mould technique, using various types of running moulds: elliptical, oval, convex-concave, cornice-shaped etc. Very often these decorations are made by running moulds at the workshop and, after the hardening, mounted at the facade in suitable pieces, but they could also be made in situ.
The methods are either with strings or curved rules - combined with specially designed running moulds in each case - followed by hand modelling with special floats and trowels.

Making running mould stucco and ashlar

As mentioned above, artificial stone walls and ashlars are often carried out with a running mould technique, as shown on drawing no. 19. Here it is only necessary to fabricate one sheet zinc reverse mould, as the running mould and the sledge can be "moved outwards" in two tempi. This has the purpose to construct the plaster decoration in 2 various layers of mortar, a rough ground layer, which has hardened before the second, fine grained finishing layer.
The running mould process starts with the executing of horizontal pointing grooves. The vertical traces are drawn afterwards in the still wet mortar. The vertical pointings are scraped in the mortar, which can be done partly with a scraper, partly with the reverse running mould, in 2-3 variuos shepes. 
The same procedure is followed for the finishing layer of mortar. Apart from this all the measures and guidelines described above under running mould have to be followed.

Photoserie II: Making running mould ashlar

A The wooden rules are placed on the masonry
B Coarse mortar is thrown on
C The running mould scrapes off superfluous mortar
D The last coat is finished
E The surface character is made

Making vertical running/turning mould for columns

It is also possible to fabricate a plaster column or a half column in the running mould - here vertical turn mould - technique. 
The column is constructed in masonry, including the necessary corbellings, leaving approximately 4 - 5 cm to a finishing coat of plaster - constructed of two layers of hydraulic lime mortar. As the turning mould can be moved outwards, by adjusting the slide pieces, there is no need for two different mould sizes to obtain the previously described two coat construction of the plaster.

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