I have a new video out on slate roofing. I started this roof/art project about 10 years ago and never finished the last side of the roof. The goal is to finish it up before the fall rains. It’s an interesting and rewarding process with lots of room for creativity. This first video covers how the slate roofing system works, cutting and punching slates, and patterns.
Slate roofs are durable, very repairable, fire resistant and beautiful. The slates are pretty easily cut, opening up a lot of possibility for creativity in design. different widths, lengths, thicknesses and colors can also be used to creative advantage. One could also stack or double slates up just for visual effect. Honestly, I’m surprised how little advantage is taken of the possibilities for making visually interesting roofs. I think that a person could make a career out of creating artistic slate roofs of unique designs. There are some pretty fancy old roofs, but they still tend to use standard geometric shapes, rather than more creative patterns, or graduating designs. Very few do large scale patterning over many slates or even the whole roof. Some of the more creative attempts that do exist end up looking rather clunky and pixelated.
The video explains the parameters that need to be observed in slating to prevent leakage, which is basically 3 inches of overlap sideways and 3 inches overlap from the top of the previous row of slates. Otherwise, aside from slate being too weak to support lots of long pointy shapes, there is a huge amount of leeway in design. Many traditional roofs are made of completely random pieces of all sizes from huge sheets to smaller pieces, as long as adequate overlaps are observed in laying them.
It is actually pretty easy to learn and do, though it is certainly some work hoofing slates up and down ladders, punching, cutting and messing about with whatever little obstacles come up. One downside to using a complex pattern is that it will take a lot longer, v.s. slapping up a bunch of standard sizes and shapes. It takes me probably close to a day to cut all the slates for one side of this roof, so that is 4 to 5 days of cutting right there. It will also take time to design. This one probably took me days to design, and I think the other roof took us a couple of days too, and it’s not even that fancy. But to me, sitting in front of that pile of slate and knowing the possibilities, is like sitting in front of a pile of great food ingredients and wanting to cook something good instead of throwing it all in a steamer, very tempting.
Slate is quarried and split on site. It has a strong grain to it and splits easily in one direction, so sheets as thin as about 1/8” can be made. Some are much thicker. The slate for this particular roof was acquired cheap as a lot from craigslist and varies from 3/16” to over 3/4” thick. It also varies a great deal in quality from very soft and probably not very long lasting, to very hard and likely very durable. Be careful buying any lots left over from roofing jobs. While it might be very cheap, and a great way to get affordable slate, it can also be full of rejects, so get it cheap and make sure there is a lot more than you need to account for a high number of culls. Variations in thickness, lumpiness, and invisible cracks can all be reasons for slates to go to the reject pile. When you pick up a slate to use it, it should be tapped on to assess it for soundness. A good hard slate should ring if it is not cracked. Sometimes just a small loose piece of slate hanging on will keep it from ringing, but slates that don’t sound right are generally put back in the pile.
New slate is quite expensive, but probably a good deal if you are thinking far enough ahead. Many slate roofs are over 100 years old, even over 200. Given the durability, you can also salvage it from old buildings and re-use it. If there are slate roofs in your area, keep an eye out, or even contact roofers and ask them to call you if they have a replacement job and maybe they’ll let you remove the slate and save them some work. The slates may be perfectly good. Many people, including roofers don’t know how to repair them, so they just replace them instead. Tragic, but it could be good for you.
Cutting slates is essentially like cutting paper. It’s a shearing action. I use a slate cutter that is a lot like a paper cutter. Traditionally, a cleaver of sorts is used with a straight metal edge. Purpose dedicated slate hammers also have a shank that can cut slates. I watched a slate artist on youtube, James Parker, who uses a hammer face to shape slates. Any slate cutting by this type of shearing action leaves a beveled edge which is nearly always placed facing out on the roof as it is very attractive. Sawn slates are pretty boring looking and not commonly used.
Hole are usually punched instead of drilled. For most slates, one good smack from the pointy end of a slate hammer will knock a usable hole. Slate hammers and even some standard European framing hammers have a pointy end for punching slates. My slate cutter also has a punch on it that makes nice clean holes. You could also use a nail. Punching slates leaves a small divet in the face of the slate, which is necessary for countersinking the nail heads below the surface. It’s still good to have a drill and countersink handy for special situations, but generally punching is faster and easier.
The divot popped out on the face of a slate punched with the pointy end of a German carpentry hammer. This depression provides a place for the nail head to nestle into at or below the surface of the slate so that it does not rub on the bottom of the slate above it.
This was a more involved project than I had anticipated, but a very rewarding one. I would do it again if I could justify taking the time (making youtube videos is a good excuse ;), but I would take more time for design. Fortunately, it is easy to mock up designs with miniature slates cut to shape from scraps, of which there are always plenty. I’ll post follow up videos here in the blog as they come out.
