We see a lot of old buildings in our work in eastern Pennsylvania and western New Jersey. Many are built of stone, which has a unique elegance but also presents some production challenges - for example, how best to install windows and doors, the components most likely to fail.
On a recent project, we were asked to repair the windows and doors of a 1760s Georgian stone building. In some cases, we were able to replace just the thresholds, sills, and sash, but many of the openings required complete replacements. In doing this kind of work, we've found that taking cues from the original construction helps us integrate modern materials and techniques.
For example, the window frames in late 18th and early 19th century stone buildings in our area are usually assembled from the same few parts: the window buck, or frame; the interior casing; and the sash. The bucks are made from two side jambs, a head jamb, and a sill, all mortise-and-tenoned together. The jambs are usually each made from a thick piece of wood profiled to include both the upper and lower stops, and sometimes the exterior back band - all molded from a single board.
Most likely, the assembled bucks were installed as the walls were being laid up. The sills and heads had "ears" that extended into masonry pockets on each side, allowing the frame to be mortared into place. If the stone courses didn't line up with the head, the carpenters inserted a large peg into the side of the jamb to serve the same purpose as the ear.
The interior casings are typically beaded and applied directly to the buck to act as a stop for the bottom sash; the bead on one side is removable to allow the sash to be taken out. After the walls were finished, the casing would be installed and loosely scribed to the surrounding stone window well. The fit didn't have to be perfect because a finish would later be applied to the sides and top of the well - either plaster or, in formal spaces, wood panels.
Removing the Old Windows
We wanted to leave the interior plaster intact, so we worked from the outside. The first step was removing the sills, which virtually fell out. Once the sills were out, we cut the nails holding the casings to the bucks with a Sawzall. We could then slip the casings from between the plaster and the buck, leaving a clean line of plaster inside.
With the casings removed, it was easy to knock out the pegs holding the side jambs to the head and pull out the sides of the buck. If the masonry was loose, the head jambs came out easily, but sometimes we had to cut through the ears to get them out.
Several of the frames were in decent condition except for the sills. On these windows, we cut through the tenon that extended from the jamb into the sill, then removed the sill, leaving the jambs in place.
New millwork. The replacement window frames were milled from white oak; the new sash and interior casings are Spanish cedar.
Attaching to Stone
After years of experimentation, we've settled on threaded rod and epoxy for securing window and door frames to stone. On the job shown here, we used 1/2-inch stainless-steel rod and two brands of epoxy, Hilti and Sika. We ended up preferring the Hilti system for one reason: The two-part adhesive comes with an extra-long nozzle that makes it easier to squirt the epoxy into the stone through the thick window bucks. This was helpful for the windows whose original side jambs remained in place. Unfortunately, though, each pack of epoxy includes only one tip and our local supplier doesn't stock them, so on complicated jobs like this we have to plan ahead and order extras. We go through a lot of tips because the particular Hilti epoxy we use sets up quickly - especially when the weather is warm.
The Sika epoxy is a one-part formulation and comes in a tube that fits a standard caulk gun. You have to use a bulk-loading sausage gun to get the epoxy out fast enough; standard ratchet and dripless guns don't have enough thrust. While the tips are not as long as Hilti's, Sika does provide an extra tip with each tube.
The process of anchoring the bucks starts with locating the holes for the threaded rod. The stone courses determine the placement and number. Ideally, we like the threaded rod to penetrate the stone at least 3 inches, so we look for stones that are at least twice that width to avoid cracking them.
Once the holes are marked and the window buck is in its exact position, we countersink a 1 3/8-inch-diameter hole in the jamb deep enough to conceal the nut and washer and allow some room for the Abatron epoxy filler we use to finish the surface before painting.
Next we switch over to a hammer drill and complete the hole through the wood and into the stone. For the old jambs, we chuck up a 5/8-inch-diameter masonry bit and continue into the stone to the required depth. With the replacement bucks, we finished drilling through the wood jamb with a 1/2-inch-diameter bit, creating a tight hole for the threaded rod where it passes into the window frame.
When the 1/2-inch bit hit the stone, we removed the new window buck, switched to a 5/8-inch bit (which allows room for the epoxy), and kept drilling to the 3-inch depth. It takes a little longer to pull the window buck out of the opening before continuing to drill, but it's worth it because that 1/2-inch hole in the wood frame helps lock the windows into place when we eventually install them. With the old jambs that remained in place, there was a little more wiggle between the rod and the oversized holes in the buck. By staggering the holes on the buck and squirting some epoxy into them during final installation, we eliminated some of the slop.
After the holes are drilled in the stone, they have to be thoroughly cleaned for the epoxy to bond well. We used a blow nozzle and a brush attachment on the hammer drill.
On projects where there are a lot of holes to epoxy, we've learned the hard way -through many wasted tubes and redrilled holes - that installing the threaded rod is a two-person operation. One guy fills the holes and the second guy inserts the threaded rods. Working this way allows us to apply several tubes of epoxy with just a single tip. But even so, it seems like you can never have enough tips.
