Slate Roofing and Repair Techniques
Slate specialist John Mahan shows how to cut, punch, and replace slate shingles.
Among modern roofing materials, slate may seem like an antique. Yet it’s still a beautiful and durable option, and many slate roofs are still in service. Perhaps the real antique is the skill needed to work with slate. In this video from the Fine Homebuilding archives, John Mahan of Mahan Slate Roofing Company in Springfield, Massachusetts, demonstrates basic slate-roofing techniques: how to cut a slate to size, how to punch a hole with a slate hammer, and how to replace a damaged slate.
Cutting slate tiles
Slate comes in different colors, sizes, thicknesses. The durability of the slate depends on the thickness. The thicker the slate, the harder it is to cut. And slate comes from the quarry already cut with holes punched. But in the installation process, sometimes it’s necessary to cut a slate to a different size, as and this is a 9 in., we want to bring it down to a 7 in. You’d use your tape guide to give you a nice scribe line. Then, you come over to the cutter and cut the slate. This is a fairly hard slate to cut. As you can see, we cut off the hole, so sometimes it’s necessary to put another hole in. You always punch the slate from the back. That would give you your countersink for your nail.
It sits flush after it’s punched and countersunk. We use copper nails because galvanized will rust out with condensation. And slate lasts forever and copper will last forever. As you can see, this is pretty much like a paper cutter.
An older method
There’s an older method of cutting a slate with slater’s stake. You would jam it into the roof. And this would be a new roof installation when you have blank plywood, not a roof above you. Drive the stake in a little bit. You would then mark your slate the same way as you would with the previous cutting method. You would use your hammer, which has a beveled edge, to chop down the side of slate. This is a much older method but gives you the same end result.
Replacing a broken slate tile
Today, we’re going to replace a broken tile. Most breaks come from an impact of a tree branch, a hunk of ice from a roofline above, or foot traffic on a low-pitch roof.
Slates are held on the roof by copper nails. As you can see, they’re not nailed tight; they’re just hung on the roof. And when they break, you would use a ripper, which is a tool hasn’t changed in 100 years. You would slide the tool up, find your nail, and pull the slate out.
As you can see, it’s not an easy process. It pulls the nails right out or sometimes they’ll break up inside the cavity. To replace the slate, you can take the slate that’s broken and measure your size. But if the slate is nonexistent, you would just measure the distance in between the slates. then measure up two inches above your bond line to ensure the water would come down onto a full tile.
There’s different color slates, so we’re going to find the right color that matches our roof and then cut it to size. In new installation, the slates are nailed into the roof. When you’re replacing a slate, you have nowhere to nail the slate, so we use a slate hook. The slate hook allows the slate to hang on the hook. The hook gets marked out at the height you want your slate hook, then you drive it in. Slide the slate up and then drop it back down onto the hook. Job is complete. The hardest part of the job was ripping the old slate out.