We’ve been fitting a chimney with dog cramps, sometimes known as coping cramps, or simply cramps. Almost like big staples, they hold masonry together by being bedded into the stonework.
Our director Phil was on top of a country house in Lancashire to show you what they are, and how to fit them. The bespoke cramps themselves are made of stainless steel and held in place with lead.
The process for making dog cramps is explained fully in the video above and is a great tool for strengthening structures.
First, a hole is chipped into across two stones in which to place the clamps. Meanwhile, a pail of molten lead simmers away for pouring. When the cramp is in place, Phil creates a dam out of clay to ensure there’s no spillage. Then, slowly, and carefully, the molten lead is poured over the cramp, filling the cut hole. It dries in seconds and afterwards is hammered down, keeping the dog cramp secure and the masonry strong.
As Phil demonstrates in the video, it’s important to keep both the lead and the stone dry. Otherwise, damp lead dropped into a bucket of molten lead can cause a bit of an explosion! Plus, if the stone is wet, it will bubble and fizz and could get messy, and ultimately fail.