• Types of brick arch
• Designing an arch
• Choosing the correct bricks
• Erecting and reinforcing a Soldier arch
• Ringed arch construction: building plans, erecting a former and bricklaying
• Pointing and finishing off
First measure across the opening and note the proposed position of the bricks (do this on both sides of the wall if you are erecting two arches). Using this information, try to place the key or middle brick—directly over the centre of the opening and so avoid having to place a shorter, cut brick at one end of the arch. Mortar each brick into place carefully and place a straightedge across the face of the wall while you are building to ensure that the arch is correctly aligned. When you have finished, leave the mortar to set for three to four days.
Then carefully life-size plan of the intrados arc on a large piece of paper or card. Measure across the springing line at the top of the opening, then go to the paper and draw a line of the same dimension across the bottom of the sheet. Mark the midpoint of the line carefully and this will give you the striking point of the arch. With this, the base line of the arch, marked, use the striking point as a centre and draw a semi-circle above the springing line with a large compass or a pencil tied to the end of a piece of string. Then lay a square or protractor along the springing line and draw a line up from the striking point which bisects the half-circle.
This gives the exact position of the key brick. Use the half circle and the perpendicular line running up through it to mark the position of each brick on the plan. Make sure all the bricks face inwards towards the striking point and that they are separated by neat, wedge-shaped joints. Once the plan is drawn out—using one or more rows of brick—it can be used to calculate the exact number of bricks needed to complete the job. Remember, though, that the total has to be doubled in a cavity or double thickness wall where the arch has to be reproduced on both sides of a door or window opening.
Former construction: To construct the former, you need a sheet of 15mm plywood to make up the rounded sides and the soffit plus a piece of hardboard to go across the top. Mark the two semicircular side pieces first, to the same dimensions as the plan. Cut them out carefully using a fretsaw. Then cut a third piece as wide as the soffit—excluding the two side sections—and as long as the opening. Attach the three pieces together by nailing along the bottom of the two side sections into the edge of the soffit section. With the frame completed, pin a piece of hardboard as wide as the soffit across the top and make sure that it is flat and level with the two sides . After you have rechecked the former against the original plan, locate it in position across the top of the opening.
Supporting the former: To hold the timber former in place during construction, you must build a small frame to fit underneath. This should consist of two side pieces with one wider cross-piece which fits across the top—although in the case of particularly wide soffits two frames may have to be built, one for each side. First measure the distance from the ground to the springing line. Subtract the width of the cross support, then cut two side bearers from 50mm square timber to this size. Fix the side bearers to the brickwork in the middle of the soffit using masonry or galvanized nails. Next, lay a piece of flat plywood almost as wide as the soffit across the top of the side bearers. Check carefully that it is correctly aligned with a spirit level and then place the timber former on top. Finally, cut four folding timber wedges and drive two from each side between the cross-piece and the side bearers. These allow you to make minor adjustments to the position of the former during construction and make it easier to remove it after the mortar has set.
Building the arch: To help keep the arch brickwork level with the face of the wall, nail four flat boards about 500mm long on each side of the opening extending from the top to the bottom of the arch. Then attach a string across the bottom of each pair of boards to act as a guiding line this can be moved up as building progresses. Start at the bottom of the arch, building each side at the same pace. As you position each brick check— with the help of a line stretched up from the striking point—that it is correctly positioned according to the original plan. Try to make neat, wedge-shaped mortar joints between each brick by putting more mortar on one end than you do at the other. Alternatively, insert small wedging pieces of slate between each brick and leave them permanently to set with the mortar.
Continue upwards until you reach the key brick, raising the guiding lines as you go. Check carefully that the final bricks are positioned correctly, especially the key brick which sits directly above the middle of the opening. Leave the mortar to set for at least three to four days—then knock away the folding wedges and remove the former. Finally, pull the side supports away from the wall and point the brickwork on the arch. Take great care when you are building or rebuilding the brickwork around the top of the arch, and use the lines you erected earlier as guides. Try to ensure that each brickwork course meets the sides of the arch neatly, and cut any bricks to fit with a hammer and bolster. Point around the outside of the entire area and then while the mortar is still wet run a soft brush across the surface.