Mailbox Vault Done: Stone Theory

Mailbox Vault Done

Here’s the scene at the entrance to the Rock Hill horse farm. The connecting wall will top out at about 28 inches, so there’s a bit more to go. The far column has some sample caps resting in place. Columns of this volume might require a massive cap to help visually anchor them. That decision hasn’t been made yet…

Mailbox Vault Done
Here’s a front-on view of the mailbox vault shortly after completion. I’m very partial to this style: structural quoins, solid stone lintels, serious gravity. It’s a mix of old school and new style. My conservative estimate puts each column weighing over two tons.

This is a plan from my tiny notebook that I eventually scrapped, in favor of thinner stones for the quoins, adding an extra pair of stones in order to make full height. I worried that at almost 7″ thick, the quoins as drawn would be out of scale to the rest of the work.

Detail looking down the quoins.

This Northern Fence Lizard spent the night resting in a nook in one the block I used for my low scaffolding. It was a very safe place until I started work in the morning. I had to move him because he was too cold to move himself. His tail is obviously shortened, perhaps by a predator, perhaps by not being careful enough around the stone pile.

Cutting Lintels

Cutting Lintels

Here is the step-by-step process I followed for cutting lintels 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.
Cutting Lintels

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.

Cutting Lintels
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.

Cutting Lintels
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.

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

Cutting Lintels


Truth window

Yesterday I got the fireplace up to mantle height. Once I have some design discussions with the woodworker about the installation of the mantle, I’ll finish out the area above and focus exclusively on the chimney. As it is right now, I have a long walk to retrieve forgotten tools.
Limited lighting in the cabin, hence the lower quality of the image.

This a view of the wedge and shims that got stuck in the end of the lintel. I’m calling this the truth window, after the openings they leave in a straw bale wall to show what’s behind the stucco rendering.

This little stone sets into place nicely, but is easily removed to see what’s behind the truth window.

The biggest spider I’ve ever seen not in a pet store. He was about two inches across, which doesn’t sound that large, but he certainly caught my attention. This is a wolf spider, a roaming hunting spider. A good reminder why I should wear gloves in the stone pile. All indications suggest this will be another banner year for black widows.

Setting the lintel

Today I set the lintel on the fireplace at the cabin in Mars Hill. The lintel is 46″ long and approximately 9″ by 9″ square. I cut it from a large slab, that weighed just shy of 1900 pounds. Here I am waiting for a fissure to emerge. I’m cutting the end of the lintel off using feathers and wedges. It’s very gratifying to listen to the stone as it splits; it sounds like ice.

Reid and Zach were on hand to help with all the lifting. We used 6″ by 6″ blocks to make a very sturdy tower in front of the fireplace. This made it much easier to lift the stone into and out of place, three times total. The first time I saw the general placement and marked the bottom of the stone for shaping. The second lift was to check the fit. I made some minor shaping adjustments and then the third lift was onto a mortar bed.

The lintel leftovers, all 1,000 pounds of it, made a good step onto the cabin porch. We will adjust grade so that the step down is consistent across the face of the step, which will effectively hide the oddball build up stones.

A couple of the drill holes on the face of the steps broke such that they can hold marbles. These are easily removed by kids, but the others are a couple of inches down a hole that didn’t break open at all. Those will be tougher to get.

Below is a detail of the break between the lintel and the step stone, just after I split them.