You’ve probably seen these cool metal stars on old brick houses and thought they were just a quaint decoration. The truth is that they are often much more than that.
Bulging or bowing in brick walls is common throughout the Philadelphia region, especially on 3 story rowhomes. Star bolts are one less-expensive way to avoid completely rebuilding the wall.
Our problem starts in the mortar used to hold the bricks together.
Unlike more modern mortar (Portland cement mixtures), the lime mortar that was used pre-1920 (or so) is subject to dissolving when contacted by moisture or water, weakening the mortar and losing both compressive strength and bond strength. Foundation subsidence may also be found to blame.
Star bolts can be used to effectively re-secure loose or bowing wall back to the original state. These metal stars are often seen on historic homes throughout the area, and are functional, not decorative (although they are attractive and interesting features).
Through the use of a grid work of 2 x 8 planks, backed by 4 x 4 posts, cables, and anchors, bulges of up to 3 inches can be reduced to less than an inch. Removal of old lime mortar between the inner and outer courses of brick (called “wythes”) is needed to further reduce the gap to plumb.
The 10" diameter "star" plates are installed on ¾” threaded rods, and anchored anywhere from 4 to 8 joists deep in the home (this can require removal of flooring or ceilings). These rods are fastened in place with washers and nuts and solid bridging (blocking) is installed between the joists. This combines the strength of the joists; essentially producing a 12x10 frame (for 4 joists) to resist brick movement, and allowing the star bolts to secure the exterior bricks in place.
Finally, the bolts may be round, oval, square, diamond, or star shaped. They should be at least 1/4" plate, and at least large enough to hold directly against at least 6 or 8 bricks. Those bricks than apply drag to other bricks around them. A 20 foot wide house face will usually require 3 bolts per floor.
When properly installed, these bolts prevent the brick facing from sagging toward the street. The framing and flooring create a structural anchor, meaning that the bricks can't move without dragging the framing out into the street.
The cost for replacement of a brick wall can exceed $8000 - Star bolts typically cost approximately $1000 each. So, not only are they functional, they are also fiscally responsible!
Star bolting has been proven for over 100 years (either as original design, or as retrofit) to maintain structural integrity. While fewer and fewer masons want to install them (they make more replacing the wall), they are a great solution to a common problem.