Two holes are drilled in the top of the rock, angled toward each other. The exact placement of the holes and their angles is determined by the mason based on his years of experience judging where the mass of the rock is. Two pins at either end of a chain or sling are inserted into the holes, and when the sling is lifted, the weight of the stone itself holds the pins in place. This seems so simple, yet the physics of it are amazing.
On the day that Terry and Kyle set the first stone of the wall in place, I had a chance to see this in action.
|These are the pins.|
|Kyle shows what part of the fork lift to|
hang them from. If you twist the chain, the rock
turns itself around as it is lifted.
|Two sizes of pins: the larger ones can|
lift 10 tons.
|Terry drills the holes...|
|and inserts the pins.|
When my rocks were quarried out the the ground, they left in place a ridge of ledge that will become one wall of sort of a courtyard. The part of the wall that Terry and Kyle are building needs to butt up against that ledge. Getting the first base rock into just the right place took many hours. First they lifted the rock into position.
They measured and eyeballed how the rock was going to fit against the ledge, lifted the rock back out of the way, and measured some more.
They chipped away bits of the rock to make it fit just right, then put it back to make sure.
They weren't satisfied, so they took it off again and flipped it over to take some off the bottom so it would lie level.
Back into place, more measuring and eyeballing.
Still not right, so they decided they needed to bring out the saw. Kyle sawed into the rock, then Terry went at it with a sledge hammer until pieces came off at a natural seam.
Then back in place to check if it's level.
Finally, they were happy with the placement of the first rock and began to place the second rock.
But they didn't like how fit against the first rock, so they needed to make some adjustments in the first rock. Kyle sawed parallel lines into the rock, and Terry whacked them with a hammer and chisel to knock the pieces off.
The second rock went back and they checked the fit.
It needed a few nudges from the forklift to get it in just the right spot.
Finally they were satisfied and called it a day (and it had been a long day). In the week since, they've added more layers to this section of the wall. Here's how it looked this morning before they came and started back to work.