Hammerhead Stoneworks

A couple of weekends ago, I led a workshop at the NC Arboretum on building stone benches. First thing in the morning we studied images of various benches, stone-cutting techniques and ways to move heavy objects safely and with relative ease. Safety was a recurring theme throughout the day. After the classroom presentation, we went outside and built a free-standing bench, a style I call castle-block for the big chunks of stone that make up the supports. The bench we built is now a permanent fixture at the Arboretum, a rest station along one of the trails.

To facilitate ease of movement, we cut the big stone down in the back of my truck. In this image, Ronnie is using a star bit chisel to notch shallow guide holes in the top of the stone. This gives the drill bit a place to sit, reducing the likelihood of the bit bouncing around and scarring the stone.

Everyone got a chance to use the drill and work at cutting stone. Here Judy leans into the drill to get the proper placement.

Since our cut edges were going to be exposed, we took some time to clean up the drill holes. Here Carol is using a handset chisel to knock off the cut edge of the bench stone. We put the cut edge to the back of the bench, less visible to passers-by.

We spent some time doing bench math, designing everything so that it would be the proper height and balanced as a structure and as an aesthetic object. Here Carol measures the thickness of the slab, the starting point for figuring out the math. I handed out the following worksheet to guide the design and layout process.

By cutting it in the back of truck, we made the stone more manageable, but it was still a heavy chunk. Jason uses a rock bar to move the stone from the pallet onto the ramps we have set up. Using 2″ by 12″ pressured treated lumber as ramps, we slid the stone down to waiting blocks and from there into place.

We used mortar to set the bench. This design can be done dry, but the mortar reduces the risk of movement, particularly since the bench is in a public place.

We all felt good as we finished up. The bench looked great and we had built it efficiently and safely. It felt good to be leaving something cool and useful for everyone to enjoy. Tre and Ronnie test drive the bench and pronounce it good.

Last week I spent a good bit of time creating this structure within the column to house the biggest mailbox I think I’ve ever seen. I cut these quoins from step slabs, using petty much every technique I know how to tim them down. The cut-off saw was too loud and dusty and the line would wander over the full 36″ of the stone. Using the hand tracer chisel worked, but was really only efficient when I was cutting the shortest lines. Eventually I settled on cutting a clean line at each edge with the small grinder and then using feathers and wedges to cut the rest. This allowed me to keep my quoins fairly symmetric, but let me go more quickly than I would with chisels alone or even using the saw. Perhaps someday I will do a time trial to see which is faster, though I suspect the old school wedges (and an electric hammer drill of course) are faster than my Stihl saw with a diamond blade on it. Feathers are more fun too.

This is a detail of the armature that I am building the columns around. This is intended to provide a place for the wooden cross pieces to be hung and held away from the stone work. By doing this, the wood is more easily maintained and switched out as needed. It also protects the stonework, by reducing the chance that the wood will soak up a bunch of water and hold it against the mortar. Whenever wood juts into stone work, it inevitably creates a weak spot in the stone structure. This armature design also provides a place where I can mount my corners template, a piece of plywood with string stretched plumb to the footer. I got this idea from Fred Lashley; I don’t know if she invented it or adapted it from some other source.

A banker is a mason’s work table. You can’t see from this angle, but this table is minutes away from falling over; it has a significant, persistent lean. That’s a chunk of Arkansas Hackett sitting on the corner.

The first designs were pencil lines on paper, as I tried to create shapes and fill the space in a balanced way. The pencil sketches were on an approximate scale. Once I had a design I liked and the clients had approved, I created the drawing above in Adobe Illustrator. I made it full scale, which means the document itself, if I could print it on a single sheet, would be exactly the size of the patio, five feet deep and almost twenty feet long. The biggest challenge was keeping the arced lines smooth. I freehanded each line, but found several shortcuts to eliminating the bumps and bounces of my hand drawn lines. I use a Wacom drawing tablet, which helps a whole lot.

You might notice that the numbering scheme is also a lettering scheme- I substantially changed the design halfway through and couldn’t start my sequencing all over again.

Since I don’t have access to a large enough printer, I had to cut the document into pieces. I outputted a couple dozen PDF files that had a shape or two on them. I twisted and turned the original document to reduce how many prints I needed. It was still a huge roll of prints. I had them done at Henco Reprographics, far and away the best printers in town. I cut each shape out, a few at a time because it proved to be so tedious. As it turned out, making the templates was just as time consuming and considerably less fun than making the stones. Though it was less dusty.

I transferred the paper shapes onto fifteen pound roofing felt. It’s considerably more durable than paper and waterproof. I fastened the paper to the felt with masking tape, to make sure my shapes didn’t morph during the cutting. Using felt for the templates was an idea I borrowed from fellow Stone Foundation member Karl Opanowicz. It worked perfectly and withstood all the abuse I could mete out.

Most of the stones had at least one straight side, which is where I started my cuts. I had to place the templates quite precisely as they barely fit on the stones. As it was, I purchased over three tons of material to find these 27 stones. There are only a couple of stones left over big enough to be cut for this design, most of which were rejected for being boring. This stone, the thickest of all of them, is sitting on the table of my Achilli bridge saw.

The Achilli bridge saw is a job site granite fabrication tool. It can support a 14 inch diamond blade and has a recirculating pump in the table reservoir that sprays water onto the blade, keeping it cool and knocking down the dust. The bluestone was so soft that I could plunge cut it, meaning I didn’t have to make multiple passes. It zipped right through.

After the straight lines were cut I moved onto the arcs. I traced these lines with a piece of soapstone. It’s more durable than pencil lines, but can be washed off as desired. The wax crayons carpenters use leave permanent markings on stone. From this picture you can see how close I am to the edge of the slab.

I used a five inch Makita variable speed grinder for the curved cuts. In this image it’s outfitted with a 4 1/2 inch blade and the grip is on the wrong side; this was an early stone in my learning curve. Matt of Rockstar Marble and Granite set me on the right course by switching me to a five inch blade and swapping the grip around. I faced the blade away from me and dragged it from left to right, sending the spray of dust away from me. By holding the grinder straight up and down I was able to get very clean and deep cuts, though I had to flip several stones to finish the job. What a delightful mess.

I used a cup wheel to grind off any excess along the edges of stones. While the sides aren’t visible, the tolerances between the stones are so tight, there’s no room for any extra material. During installation on site, I also used a zero tolerance wheel, another granite fabrication tool, to fix shapes and tighten the joints. These are both fairly aggressive tools and I was able to rip my way through the excess without too much trouble.

Towards the end of fabricating I laid it all out at my workshop. I didn’t fuss too much with the joints while I was fabricating it, figuring that there would be a lot to do on site to get it exactly right. It would have been hard to get them exactly right at the shop because the stones were varying thicknesses placed on a level surface. A slight discrepancy in level can change the way two stones interact. Most of the stones needed at least some attention to snug in the way that I wanted. The stone fabricated above- number 9- is visible at the bottom left of this image. On the patio, it partly spans the doorway, one of the reasons I chose such a thick slab.

Here is the step-by-step process I followed to cut the lintel for the pig roaster.

Here’s the stone I’ve selected and an assortment of the tools needed. The blue lines on the stone represent the cuts I’ll be making, one way or another. I decide to cut the right end off first, using feathers and wedges.

Before I use the hammer drill, I make small starter holes with the star-bit chisel. This prevents the drill bit from chattering on the stone, missing the mark and leaving unsightly scars. Before hammer drills, star bits were a traditional way to cut stone- swing the hammer, spin the chisel, swing the hammer, spin the chisel and on and on.

When cutting granite, I usually put feathers and wedges on three sides. To help guide the cut through the edges of the stone, I use my hand tracer, a recent purchase from Trow and Holden, to score a line where I want the cut to go.

Sweet!
An argument could be made for making this cut with the hand tracer alone; granite is hard and heavy, but it behaves very well under tools. I decided to use the feathers to save time. You should trace all four sides and that’s no small feat with a stone this large, at least working by yourself.

I followed the same process to make the longer cut along the width of the stone. Note how much straighter the ends are, where I traced the edges before splitting. It might have been a good idea to trace the whole line, though the rough line is in keeping with the overall aesthetic. I placed one wedge at the bottom of each side to guide the line.

The pencil line indicates the last cut to be made, to trim the top of the lintel. This is the face of the stone, freshly split showing a lovely line of quartz that will center over the opening of the roaster. Because of the clean line I want and the proximity to the edge of the stone I elect to use the hand tracer rather than the drill and wedges.

Here’s the risk of this operation- I am cutting very close to the edge of the stone, particularly as it tapers towards the bottom. It is very likely that the cut I’m making will choose the path of least resistance out of the stone, which would be to the back, rather than the bottom. The top of the stone will spall, leaving me with stone to remove by other means.

The hand tracer is surprisingly effective; it cuts a very, very clean line.

Unfortunately the top of stone spalls, leaving excess material on the top where my cut was trying to remove the thinnest flake of stone. The blue line indicates what remains to be removed. The grinder is my weapon of choice.

I score the top of the stone with my seven inch grinder using a diamond blade. I put the score lines about an inch apart. I then use my chisels to remove the excess material. Notice the dimple on the face closest to the camera; a matching dimple on the opposite side made it possible to lift the stone.

All that’s left is cleaning up the drill holes a bit.

Up to this point, every time I’ve cut a stone using feathers and wedges, I have done so in a straight line. I decided to trying cutting a S shape out of this particular slab of sandstone paving because it was just too large for the walkway under construction; it would unbalance the whole composition. I wanted a sinuous line to accent the rolling shape of the path and to avoid creating a uniform, tiled feeling with long straight lines and square stones.

I drew the line over a few times, trying to get the right shape. I wanted a subtle curve, figuring it would be easier to accomplish. The X’s indicate where the drill holes be, evenly spaced. This is the back of the stone, so my scribbles and drill marks will be unseen.

I drilled six holes. Why six? Because that’s how many complete sets of feathers and wedges I had at the time. More would have been better. The holes are fairly shallow, about two inches. The stone itself is only three inches thick. I was careful to not punch the drill bit through the stone, as it would have created ugly knockouts.

I placed the wedges so that they turned along the line. This ensures that the force applied pushed the stone apart along the desired line. They look like soldiers marching.

Ah, so close. The actual split wandered from the desired line at the very bottom of the stone. Looking at it now, it’s clear that the split followed the path of least resistance. Another wedge even closer to the edge might have helped this, as would have reorienting the line so that the desired line followed the path of least resistance. Tracing the desired line with a chisel might also have been helpful.
There’s a lot of surface flaking where the feathers are set. I believe the wedges are a fraction to big for the drill holes so that they bind at the top and cause the stone to pop like this. This was a secondhand set of wedges that I have since replaced. Another reason to do this on the bottom of the stone.

Here are the cut stones in the pathway. The two big, rust-colored stones to the left side of the image are the cut stones flipped and set. Note the ‘dog paw’ pebbling just above the gray stone, to honor Dixie, a regular visitor to my lunches during the project.

This photograph showing how to cut a stone is being used on the Wikipedia page devoted to feathers and wedges.

I lost a wedge and set of feathers in the lintel stone. The stone broke cleanly, but this wedge, at the front edge of the stone, didn’t split quite right. The wedge remains, well stuck in the stone. In this picture, the wedge is set about two inches back from the front of the fireplace. I am leaving a ‘truth window’ in the stonework, so that you can look inside this little pocket and see the stranded tool.

This is my work space in the cabin, morning light filtering in. The recessed floor is where the hearthstones will be set.

There are marbles throughout this project, including this playful little dragon, well hidden in the face of the fireplace.

This tiger beetle has been a shiny emerald skittering around my stone piles.

This spring has been the wettest in years and the salamanders are in seventh salamander heaven. Everyday I see a few, under stones, in the creek or sometimes just walking around in the damp leaf litter. I believe this to be a Mountain Dusky Salamander, but I am not certain of my ID.