Brick arches were traditionally used for structural support. Today, they are a popular choice of decorative element for doors, windows, and indoor openings.
Building the Support:
Firstly, measure the opening’s width at it’s highest point before it forms an arch. This will form the base of the wooden arch support and is known as the springing line. Then, transfer the measurement of the opening to the bottom edge of a sheet of plywood. Find and mark the centre of the springing line on the bottom edge of the plywood to find the striking point. Then, tie a pencil to a piece of string and place the nib on one end of the springing line. Hold the string taut and place the other hand on the centre point. Draw a half-circle from one end to the other end of the baseline.
Draw a vertical line that runs perpendicular to the springing baseline from the centre point. Mark the point that positions the keystone where it bisects the half-circle. You can then count how many bricks will be needed on either side. Use a jigsaw to cut out the half-circle and use the shape as a template to cut a second one. These will form both sides of the wooden support.
You can then nail a piece of lumber to the base of the half-circle. Nail smaller lumber pieces along the perpendicular line and two more on either side to form a triangle. Then nail the other half-circle piece of plywood to the lumber. Nail a strip of flexible hardwood to the plywood’s curved edge.
Building the Arch:
Build two pillars on either side of the support to a height that ends at the point where the arch begins. Make sure that the pillars are deep and wider enough to support the arch. Cut a horizontal length of lumber the same width as the opening to go under the base, and two lengths of lumber to go against the side pillars. Place the half-circle plywood support on top of this frame. Together, they will support the formation of the arch while the bricks are being placed. Maintain balance by building equally on each side until you reach the point where the keystone will be placed. The keystone should be carefully wedged into the area at the top of the arch where it will lock the bricks into place and transfer the load onto the pillars instead of the wooden form.
After the mortar has set, remove the support frame.