Synopsis: Mason John Carroll walks through the process of building four semicircular brick arches for the support structure under an addition. Step-by-step photographs depict building and setting the forms, laying the first and subsequent courses, revealing the inner arch, and finishing the joints. Carroll explains how to calculate the brick spacing for each course, and which tools best fill, pack, and mold the mortar for a concave profile.

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I’ve been doing masonry work for decades, and the vast majority of that work involves setting rectangular shapes down in straight lines. But once in a while, I get to work outside the straight lines and build brick arches, which demand a higher level of planning and layout. I recently built a series of brick arches for the support structure under an addition.

Although the arch is a very strong and time-tested architectural element, the arches for this project were mainly aesthetic. The actual support for the addition came from six cast concrete pillars that were placed before I arrived. My job was to add brick veneer around the columns and then to connect the columns with arches: four semicircular arches (what I call Roman arches) on the sides and a segmental arch at one end. This article will cover my approach to the general process of laying out and building the Roman arches.

The grade under this addition sloped down, and on the higher side, the contractor had joined the columns with poured-concrete sections at bench height, while on the lower side he left those spaces empty to provide walkout access. The first task was laying the brick veneer around the concrete columns up to where the arches would begin. I went 18 courses high, and with some careful planning, the top courses all ended up three bricks wide, which gave me an all-important consistent starting point for building the arches.

Space the bricks

I planned to lay the bricks for the arch in an offset (staggered) “running bond” pattern. To have the same pattern where the arch meets the columns on both sides, you need an odd number of courses. To lay out an odd number of courses on an arch, masons start with a “keystone” brick that straddles the exact center of the arch.

From Fine Homebuilding #298

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Related Links:

• Expanding an Opening in an Masonry Wall
• Best Practices: Methods for Installing Brick or Stone Veneer
• Brick Fixes
• Keep Craft Alive: Clay Chapman, Mason

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