Figuring and Building a Brick Arch Template
Preparing and building a brick arch template in the field will allow you to add an opulent feature to an otherwise simple brick veneer.
By Steven Fechino
As construction grows busier, the opportunity for creative masonry installations increases and can allow for projects to have more decorative features. These include corbels, quoins and arches. Arches can add a great feature to an otherwise simple brick veneer with just a small amount of preplanning. This article will discuss the details in preparing the template for constructing a semicircular arch in the field.
Before building a brick arch template, you must understand a few terms. The arch must be held in place by a mass (the wall on each side of the arch), and this is called the skewback or abutment. The abutment is where the bottom of the arch connects to the veneer, and this will keep the arch from “kicking” or “opening” up. The height of the arch at the greatest point is called the rise of the arch. The rise may not be the same everywhere on the arch; it can vary. The span of the arch is the distance between the abutments, and this will be the distance between the jamb openings. The key or keystone of an arch is at the top of the arch, directly above the center of the arch. It can be decorative or of similar materials with which you build the entire arch. In any case, the keystone is the last unit laid when constructing the arch, and it is the basis for the layout.
When building the template, a few details can make the carpentry easier. Consider building a small 60-inch arch template: The brick arch that needs to be constructed has a rise of 12 inches. To calculate the radius of the arch (this in not the radius of the arch template), you have a four-step calculation that will allow you to lay out the arches on your project with consistency, no matter the span or rise of the arch. To begin, take the span and divide it in half, which will give you 30 inches. Then take the half span of 30 inches and multiply it by itself, this will give you 30 inches times 30 inches, or 900 square inches.
It gets easier here: Divide the square inches of 900 by the rise of the arch (12 inches) and you have 75 inches. The radius of the arch is not the same as half of the span. If that were the case, you would not be able to vary the height of the rise. The radius is where the arch semi-circle begins and intersects with the abutments. To calculate the radius, take 75 inches (900 square inches/12-inch rise) and then add the rise of 12 inches and divide by 2. This will give you the radius of the arch, 43.5 inches.
To lay out the template, take a sheet of plywood and subtract ¼ inch from the radius, so that the arch can wedged and braced into proper position and removed once constructed. This leaves 1/8 inch on both sides of the arch. That gives you 43¼ inches from the 96-inch edge of the sheet of plywood. From the center point, you can draw the radius that will be cut to fit into the sides of the arch template. Since the radius is only 43¼ inches, the single sheet of plywood will easy be enough to construct into the template. When cutting the plywood, a circular saw will allow you to easily cut the radius. Simply set the depth of the blade about 1/8 inch deeper that the material to be cut, and slowly cut backward, turning the saw and following the lines you need to cut. The arch template should not be wider than the material that you are using to build the arch. This will allow the layout marks to be easily made and easy to see while laying the units. The interior of the template can be made with 2- x 4-inch scraps of lumber that create a frame to join the radius plywood. I prefer using screws when making a template as this is easier to fix when I make a mistake, and it is easier to disassemble when removing the arch template, if necessary.
I have seen several methods used to line the top of the arch template. I have seen ¼-inch paneling or card board, or just leaving it open. I prefer to leave it open and to keep the joints on the bottom of my units open that turn the arch. This eliminates cutting out mortar when the form is removed and will allow me to tuckpoint the joints cleaner and easier. Depending on the time of the year, the material being laid, and the skill of the mason, other techniques can be just as effective as what we have discussed and can be performed with excellent results. All arch templates require bracing to secure the template during construction as well as to support the weight of the arch. Do nor skimp on the bracing, and take the extra steps, if necessary, to perform a safe installation.
Steven Fechino is engineering and construction manager Mortar Net Solutions. Steven has 35 years of experience in masonry restoration, moisture management and hardscape construction.