Location: Blackheath, London
Blackheath Halls: Circa 1895 Architects: James Edmeston and Edward Gabriel.
The main auditorium ceiling is an original fibrous plaster construction, the first patented process of such fibrous plaster works dated back to 1855, whereby fibrous plaster sections are built up
into large independent units and attached to structures at comparatively few points.
Casting usually consists of plaster of Paris reinforced with wood laths or battens and layers of mesh jute hessian. Layers of plaster are then applied in differing methods of brush and splash coat.
It is a system that allows the cast sections to be applied to a preformed timber framework as separate casts which are then made good to become one ceiling. The precast sections were installed through a system of mechanical fixings, nails and hessian/plaster wads.
The Ceiling at Blackheath Halls is made up of 8 number major beams with enriched soffit, these then divided with 9 number minor plain beam panels. These smaller minor beams being fitted across the width and length of the ceiling to create 2 runs of 20 number (Squarish 1 metre by 870mm) coffers across the width between each major beam.
Two large ceiling roses provide visual points to the central line of the ceiling.
Overall it was in a good condition but it was exhibiting all the signs of age that would be expected of materials of such longevity. The plaster and hessian had become fragile and the friable nature of the plaster meant there was a danger that the timber lath within the casts would start to fracture away from the plaster.
In addition, there were several areas where failure and collapse of the original beam mouldings were apparent, caused by the loss of the original fixings between the plaster casts and the timber framework below.
On top of the above structural evidence of ageing, there were also several examples of damage caused by the poor standard of historical lighting and sound equipment installations.
This ceiling had come to an age when it required some sympathetic maintenance and repairs to allow it to remain in place for the next generation. If these works were not completed, then the gradual process of disrepair would have continued at a faster pace and the deterioration of the fixings would have applied more pressure on the remaining sound areas.
The repairs were completed using different methods which included the following:
- Major beams were re-secured with wires and plaster wads. All fixing locations pre-determined to ensure that true fixing points were created through both the casts and into the timber framework behind
- Minor beams were re-screwed directly into the timber framework beneath.
- Major cracks to the beams raked out to an adequate depth and to firm sides to allow the insertion of a hessian and white plaster caulking. Once caulked all filled and finished flush and smooth in white plaster.
- Care must be taken when applying mechanical fixings to a brittle construction such as these ceilings. To gain the full benefit of these mechanical fixings it is important that the application connects with the timber lath that is sandwiched in canvas and plaster within the fibrous cast, and then through this lath into the timber framework from which the fibrous plaster is suspended.
Once this is achieved then very gentle pressure needs to be applied when tightening the fitting to ensure no damage is caused by fracturing the immediate area.