The first apprentices began to work on cutting and finishing ashlar shaped stones, these being generally rectangular cuboids. In order to complete these stones, they had to cut joggle joints. The hand cutting of these was taught to them by Chris Hannaway very early on. They had to cut the joint into the correct end so that they would match up with the next stone when set in place on the South Tower. It would be five years before these stones would go up on the Tower. By then there would be approximately 8,000 stones waiting in the stoneyard.
How Joggle Joints Were Used In Erecting The Tower
This type of joint is used when a stone is mortared to an adjacent stone with corresponding grooves keying the stones together when the mortar sets up. According to Master Mason Steve Boyle, this was common practice in load bearing masonry along with “frogging” of the joints. “Frogging” is where the joint is roughed up with a point or chisel. Sometimes small pebbles were dropped into the joint to further lock the stones together.
“On the Tower, the method we used for mortaring the vertical joints was to initially point up the joints front and back and after the initial set, pour them full with grout.“
– Stephen Boyle
Boyle goes on to indicate additional setting techniques for other shaped stones. He says, when setting trade work, e.g. the gablets, where the bed joints for many of the stones were not horizontal, it was not practical to spread the bedding mortar in the way that ashlars and quoins would be bedded. These stones were dry set on packings. The front and back of the joints were packed with oakum and subsequently poured with grout. Similar grooves were field cut into the joints of the stones prior to setting that were specifically to help the grout flow freely and reach all surfaces of the bed or joint. The oakum was removed after the initial set of the grout and the joints pointed with mortar.
- Special thanks to Steve Boyle and Timothy Smith for the information in this post.