Gauged brickwork is the highest class of work available in brickwork. The arch, in this case, or other enrichment, must be accurately surveyed, drawn 1:1 scale, templets made, and the rubber bricks cut. These in turn must be perfectly squared on two sides before they are cut to templet size and rubbed accurately until they fit the drawing. The opening in which the arch is installed must be accurately set out before each arch can be constructed. Finally, when the arch has been constructed and has set, it is rubbed with a pumice stone and pointed up. Gauged work is perhaps among the most satisfying and fulfilling of all types of brickwork.
An example of a gauged arch constructed in the 19th Century as a replacement for original 18th Century work. It is badly decayed due to the use of hard cement mortars both above and in the arch itself.
Brickwork above the arch had suffered because of modern interventions and inappropriate materials which had then cracked and sagged. Water ingress and associated decay mechanisms affected the survival of the arch.
The openings are carefully surveyed, and a life size drawing produced using accurate geometry skills. Templets are cut and marked up for cutting the rubber bricks.
Often, arches can be prepared in the workshop but in this example the arches were cut and rubbed on site using a potting shed as a temporary workshop!
The decayed arch and brickwork above the opening is removed to allow access to construct the new arch. Here, a lintel is installed as these are flat arches. Camber arches, those with a very slight rise in the centre, would be built over a former and would be self-supporting. Accurate setting out is vital and the preparation of the existing brickwork to receive the arch is painstaking to achieve the right finish. Here a line is taken from the striking or vanishing point of the arch (taken from the drawing) to test and check the cutting of the angles of brickwork and the laying of the arch voussoirs. This arch has been designed with joints of 2mm.
Once the arch is drawn, templets are prepared to which bricks are squared, marked cut and rubbed until they fit the drawing exactly with the required joint width.
The voussoirs laid in lime putty mortar according to their positions taken from the drawing and accurately marked on the lintel or arch former. They are then checked using the line emanating from the striking point and a pre marked staff on top of the arch. Here the key brick is being laid to complete an arch.
Rubbing the face of an arch will remove all imperfections before the joint lines are revealed and pointed up carried out as required.
The brickwork above the arch has been reconstructed and laid to line prior to pointing up. Where possible, original bricks have been reused. Where inappropriate modern bricks had to be replaced, a 60mm soft handmade facing brick is used. The brickwork is reconstructed based on photographs of the original & pointed with an appropriate putty mortar and penny struck finish. No lintel is visible underneath the soffit because it is set back far enough for its edge to be covered by either the window trim or by pointing. Camber arches in whose soffits are visible on the other hand, must have a nicely finished soffit too.
Another arch, this time on an upper floor. In addition to the obvious decay, this arch had been badly constructed again as a repair during the late 19th Century. The joint thicknesses varied between 1-3mm, an even number of voussoirs had been used with no key brick and the angle of the skewbacks (angled bricks at each end was incorrect.
The completed gauged arch. The original oak window frame and glazing were completed by artisans skilled in these crafts.
A gauged flat arch c1800 for a garden pavilion. This one had been particularly badly treated (above). The brickwork was repaired & repointed using a hot mix mortar. The arch, a relatively simple design matching the design of the original with a 3mm joint of mature putty & silica sand. The new oak window was caulked using oakum tar hemp and lime putty.
Carpentry by Chester Conservation Joinery
Glazing by Norgrove Studios
Gauged camber arches are very common in England’s towns and cities, and they are one of the most common features of Georgian era brickwork construction. The camber was intended to remove the optical illusion of sagging from the flat arch and it was a device which became necessary when, following the Great Fire of London in 1666, it was decreed that windows had to be set back inside the opening and as a result could no longer be built over door and window frames. It is of great value to the survival of the craft and a matter of great personal satisfaction as well as historical authenticity to be able to draw, set out, prepare and construct a gauged camber arch using high quality rubbers available from a small number of traditional brick manufacturers.
Setting out and construction of a gauged camber arch requires a high degree accuracy in surveying the opening where the arch is to be built and in setting out the position of the arch. It is very important that the central striking point location, taken from the drawing, is accurately positioned. A wooden staff is used marked up with the marks of the voussoir positions at the extrados (top of the arch) and this, in combination with the line attached at the striking point, is used to check accuracy during construction. This photo shows several radiating lines for demonstration the degree of accuracy but in reality, only a single line is used for this purpose.
A gauged camber arch differs from a flat arch in that a camber is drawn into the arch drawing to give the arch a very slight rise in the centre. The arch is built over a timber turning piece and on this, the positions of the voussoirs are transferred from the drawing. The soffit bevels must be rubbed carefully to sit correctly and run seamlessly across the turning piece.
This arch was built with joints of 1.5mm but like the brick work to either side of it, has been tuck pointed, the latter with colour washed red dressings and yellow stocks bricks in a style common in parts of Southern England. The face and top of the arch is rubbed down with pumice once the arch has set, the former to remove any slight deflections & imperfections in the voussoirs when laid, the latter to ensure that the arch is ranged with the brickwork either side of it. The timber turning piece has been removed or ‘struck’ and the arch is self-supporting.
On this Bayworth Construction project in Oxfordshire, Terrence Lee Conservation was employed by Kent based, Georgian Brickwork. Its owner, Charles Reilly & Terrence Lee built 8 curved on plan gauged, cambered arches images of which are shown here. The working drawings, rubbers & polystyrene formers were produced by Lambs Brick & Stone to an extremely high finish. It was then up to the bricklayers to set out and ensure that the rubber bricks worked around the curvature with 2mm joints to give a fine classic finish.
Terrence Lee Conservation is grateful to Georgian Brickwork for the opportunity to be involved in this complex and rewarding gauged brickwork project.
The curved shape of the building known as crinkle crankle shows how the arches were constructed to fit the curvature of the walling.
Lambs bricks used for this project supplied in their transportation packs. They are superbly manufactured but still required careful rubbing in order to fit in with the nuances of the openings for which they are intended.
Preparing an opening to a high standard is a time consuming but necessary process if the arch is to fit accurately. As with any arch or enrichment, the setting out for curved gauged arches requires consummate attention to detail. Here, the bricks at the rear of the opening have been chopped back to ensure they do not impede the construction of the arch. The former inserted to support the newly constructed arches. Once constructed this would remain in position until the arch had completely set.
The rubbers are set out dry initially to establish their exact position in the arch and to ensure that the joints sizes are even. At this point rubbing of the bricks is carried out.
Laying voussoirs in an arch with 2mm joints requires the upmost concentration, patience and a zero-tolerance attitude to error.
A Completed arch. Note the curvature & slight camber at the intrados of the arch.
A top floor arch, 1 brick deep in face, freshly laid with squeezed putty bead showing. The hollow cross joints were cut during the manufacture of the bricks and will be filled with lime putty mortar as part of the pointing up process. Note the joint marks on the polystyrene former. The exact angled position of each rubber is checked using a cord attached at the striking point.
The same arch shown pointed and finished, the top rubbed to form a continuous even curvature. The brickwork above can be rebuilt once the arch has sufficiently set.
A completed top floor arch.
On the face of it there doesn’t appear much wrong with this original C18 elliptical arch for a carriage house on a Grade II listed building. Close inspection by Terrence Lee Conservation revealed slippage of the brickwork above the crown causing the voussoirs to pivot outwards and cracks appear through the 2mm putty joints. Cement repairs have been carried out to the springer brick and voussoirs on the LH side of the arch.
The brickwork above the arch is supported using strongboys and acro props. Loose, slipped, or damaged brickwork is removed carefully from above the affected portion of the arch (the crown). To ensure accurate repair and in the case of the worst scenario, total collapse, all information is recorded that might be needed for either repair or complete rebuild. To do this, acetate is stretched across the opening and used to mark all voussoirs positions which are numbered, the joint lines drawn. The extrados and intrados lines are also applied to the acetate whilst the rise of the arch measured.
Here, a timber former has been constructed from a drawing of the intrados and extrados using the ‘string’ method of elliptical drawing which is not appropriate for drawing in the joints on a drawing (see below). Details of the exact voussoirs positions are drawn on the former & numbered. Damaged bricks, including the broken springers and cement covered voussoir on the left hand side as well as further bricks from above are removed once the structure is safely supported. Close recorded inspection of the innermost brickwork is also carried out at this point.
Note that to draw a complete (with all joints) true elliptical arch, a two-part trammel can be used. This will ensure total accuracy of all aspects of the drawing. This video (below) shows the author being trained by Charles Reilly of Georgian Brickwork in elliptical arch drawing, something considered essential by the author before undertaking a project of this nature and complexity. If the arch had to be completely rebuilt, this knowledge would be applied and would enable the cutting of new rubbers to make voussoirs. Training of this type helps to build an understanding of how brickwork features such as these features’ are constructed.
The completed elliptical arch cleaned of staining, repaired & rebuilt. Note the 4 courses of new cut & rubbed voussoirs to the left-hand side of the arch and the replacement springer brick underneath them. Matching hot lime mortar has been used to rebuild the brickwork above and repoint as required. Stainless helical bar and other stainless fixings have been used internally to help support the brickwork above and to anchor it to the inner core of brickwork.
