Working Techniques and Repair Methods for Plaster Decorations on Facades
By: Søren Vadstrup

11. Reconstruction of missing plaster decorations on facades

On deteriorated and damaged plaster facades, there will often be missing some parts of the structure. They can be fallen off, or they are taken of or moved away of safety reasons.
If it is pieces of "plain" plaster, a piece of a cornice, a frieze or the plinth, this can immediate be remade, as described in the previous chapter, as the form is very simple. 
But if the missing part is a more complicated, sculptural or decorative elements, it is a much more complex situation. 
If we are dealing with a piece of art of great artistic or architectural value, and nearly everything is lost, it is very difficult to justify to make a reconstruction, because the artistic value often are strongly connected with the artist, who made it. A contemporary artists reconstruction will always be a uncertain rendition.
More common, but still complicated sculptural elements, which are missing, needs a certain procedure in order to make a proper reconstruction:

1 First step is to make a conscious and profound documentation and measurement of the original remains.
2 Next step is to carry out a historic research to clear up the age, history, possible artist/craftsman, possible drawings, paintings, photographs, descriptions,  etc.
3 Now we are ready to produce a reconstruction drawing, which involves:
   The measurement of the possible remaining parts, including
   The traces at the spot of the original form
   The historic research: Photographs, drawings etc.
   Similar decorations or elements on the same building/facade
   Similar decorations or elements on other buildings from the same period
   Knowledge to the art- and architectural history of the building and the period.
   The preservation and incorporating the most part of the surviving, original element
4 After approval of the reconstruction drawing, the reconstruction is carried out in full scale, in case of a very essential piece, with a full scale reconstructed model, possibly in gypsum, as a phase in between.
5 The reconstruction is mounted and fitted to the original place, without destroying any part of the original element. A visible joint to show what is old and what is new could be considered, if this does not cause technical or aesthetic problems.
Recasting and reconstructing deteriorated cast ornaments
As a very common damage on plasterwork on facades is bursting of cast ornaments in Portland cement, due to corroded iron mountings, directly fallen elements or deteriorated surfaces, it is often necessary to re-cast an old cast element.
1 The original element is carefully de-mounted, cleaned for crust, dirt and paint layers. 
2 If possible an exact identical, but complete element from the facade is chosen and similar cleaned in situ.
3 A reverse mould of the cleaned element  is made - even if it is broken or parts are missing. This is done by making a thin squeeze in 2-component PVC-rubber etc. and at the same time putting a hard backing made of gypsum, reinforced with sticks etc. at the flexible rubber mould, to prevent later misshapenness, when it is removed. 
4 If parts of the original elements is missing, a right/positive cast is made in gypsum from the reverse mould. This cast is completed by hand modelling the disappeared parts in gypsum. From this reconstructed model, a new squeeze in 2-component rubber, including a reinforced backing, is made as a reverse mould for the new cast of the completed element. 
5 The new element is cast in wet, ordinary Portland cement and gravel 1:3 with suitable water, pouring first a thin layer, which is ģhelpedī out in every corner and detail of the mould, to prevent air holes, missing corners or bubbles.


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