Property Maintenance Repairing And Restoring Brick Or Stone Features Arches
Before work is undertaken it is imperative that accurate and detailed measurements are taken of the existing structure in position. These will be used to reproduce a drawing and also a detailed specification of the original structure. Such details that should be noted will include the size and the shape of the feature, any special moldings and molded bricks in the repair as well as those that need to be ordered from suppliers, the type of masonry used in the original construction, the bedding material and its constituent parts along with the style of pointing of the finished work.
The plan or drawing you want to prepare should clearly show the proposed work in elevation. Extreme care should be taken to note any number or sequences of the bricks or units that are required to be salvaged. These then should be clearly shown and the same numbers marked on the corresponding unit as are taken down, cleaned carefully and stored ready for reuse.
The drawing must also show in as much detail as is possible any subsidiary work that may be required with the restoration, together with its specifications. If the work necessitates the use of moldings then they should be drawn to larger scale, or even full size, so that replacement units can be reproduced accurately. It is important at this stage to bear in mind that once the feature has been entirely demolished any accurate reproduction will depend entirely on the drawings that you have produced so all mistakes and omissions will be impossible to correct later. Photographs would certainly be helpful.
Special features in brickwork have mainly been produced in either fine axed work or gaged or rubbed work and would include: balustrades, capping to parapet walling and piers, cornices, string courses, dog-too thing or dental coursing, block bonded quoins, plinths, herringbone and basket weave panels, brick lintels, arches and niches.
When attempting to reproduce fine axed work the following is an outline of the general procedures for preparing the voussoirs for a fine axed arch. This procedure may vary slightly to suit the different types of arches but the basic principles still remains the same. An outline of the arch should be set out on the setting out board. Mark out the position of the voussoirs on the extra-dos of the arch. If the arch has a key brick or stone, then the voussoirs are set out by marking out the key brick or stone first and dividing the extra-dos into a number of equal division which must not be greater than the width of the bricks being used plus the thickness of the joint.
If the arch is to be bonded on the face side, there must be an even number of voussoirs each side of the key brick or stone as this will ensure that the springing brick will correspond with the key brick. When the common size of the voussoirs has been determined, complete the arch by drawing the bed joint lines between the extra-dos and the intro-dos so that they radiate to the striking point of the intended curve, thus ensuring that the arch courses are normal to the curve and maintaining a even bond in a two ringed segmental arches.
It should be noted that brickwork and stone arches need to be in compression and will benefit from loading. Where extreme loading is anticipated, parabolic arches are advised as this form of arch is the strongest in compression. Particular care should be taken with regard to lateral forces, and imposed loading from roof trusses being transferred from the arch trough the masonry and into the flank walls and reveals.