the Carpentry Way: Gateway (XIV)                                                          

Gateway (XIV)

Post 14 in a series describing the design and construction of a kabukimon for the Museum of Fine Arts in Boston. The previous post can be found here.


Yesterday was  one of those longer days, a day featuring warm weather, quick setting mortar, and large chunks of granite. I recover slowly today - nothing seems permanently damaged on my body as far as I can tell. My wife was on hand to lend moral support, wield the camera, and help me out where she was able.

The first task after arriving and getting the truck unpacked was to mark out the positions of the granite pieces on the concrete pads cast last month:

From the outlines for the stones I marked locations inboard for the jacking bolts to be placed. Out comes the hammer drill next for a bit of good vibration:

I had my small compressor on hand to blow the holes clean:

The inserts were dropped in and set with a hammer:

Here's one group:

The jacking bolts get threaded in after that:

The bolts are initially placed so as to be about 1/2" off the surface of the concrete.

The front posts, wall posts and sills were tackled first, after which I could move on to the rear support post, which feature parallelogram-shaped stones:

More drilling and insert fastener installation followed:

It has rained several times in the interim since I did the concrete work, so I gave the site another tamping to make sure everything was nicely compacted down around the concrete:

There are eight granite blocks altogether, and four of them were small and easily carried over to the site. The other four were a different matter, and were at the limit of what I could lift, let alone carefully maneuver as need be. I spent a fair bit of time in advance thinking out how to best move the heavy rocks by myself. In the end I came up with a plan involving a small bit of staging on wheels. The staging has an adjustable plywood deck level, so I set it to be the same height as the back of my truck deck. Then the block could be wiggled over and onto the stage from my truck deck:

I then popped it up onto a couple of battens:

At the top of the stage I had rigged a 6"x6" pine beam with a pair of plywood pieces to give the stage a bit more rigidity. The stone could now be easily rolled onto site:

Once the staging was placed over the location where it needed to be placed, I proceeded to rig it with a pair of 500lb. rated ratchet straps and a metal lifting hook I had fabricated:

A 2 ton come-along was rigged next, anchored to one side of the stage and with a lifting point affixed to the 6"x6" beam above:

With this arrangement, the stone was easy to lift:

Once lifted, the plywood deck could be removed, thus allowing the stone to be lowered down:

I often have that slack-jawed expression when I am concentrating - please pay it no mind.

The stone was lowered until it started to locate on top of the stainless all-thread rod:

A couple more inches lower and the stone was sitting on a pair of sawhorses. This intermediate rest position allowed me to re-rig, swapping out the metal hook for a jatoba lifting spacer/bracket I had fabricated:

This new arrangement allowed the stone to be lowered all the way down while the threaded rod emerged out the top, without interference. The jig also made it relatively easy to determine where the center of mass was so that the stone could be lifted nice and level.

Another 500lb. ratchet strap was fitted as a lifting sling:

A small amount of lift allowed the sawhorses to be scooted to the side:


The stone comes to rest atop 4 jacking bolts:

The stage ensemble was removed, wheeled back over to the truck and the process repeated for the other main post granite support.

Then it was time for the sills, which measure 6"x8"x46". These are the heaviest pieces in this set up. Here's the first one parked onto the stage, moved into position and getting rigged for lifting:

Same process as before brings the stone to the ground, except that there is no need to re-rig halfway as there are no threaded rods involved:

You have to be quite careful with granite where any sharp corners are located as it can chip quite easily. Most of the corners on these pieces are chamfered, but for the areas left without chamfer, the lifting mechanism gave me peace of mind and control over the process to ensure no mistakes were made.

Once all the foundation stones were set in place, the process of rough leveling commenced. A good way to do this is to take some preliminary elevations with a transit and decide which ones have to come up and which ones have to come down:

My wife held the tape measure at each location while I spotted.

The four point jacking allows the stones to be precisely leveled in both axes:

The sills are leveled and also set at a height relative to the post supports to either side:

Once all the stones were leveled and checked several times over for height with the transit, it was time for the mortar. I used 'precision grout' which is used mostly for leveling machinery to be set up on concrete surfaces. It is a type of grout which does not shrink. As with concrete, once the grouting gets mixed, you have to move quickly and without getting sidetracked.

I mixed the grout for the front post stones first. I used a pry bar to lift them up enough to place a blob of grout under the middle, such that when the stone was lowered back down it would squeeze the grout out to the sides. This ensured that the stone was completely bedded on grout and there were no voids. Later, grout is packed in from the sides and dressed flat.

With stone one and two grouted, I quickly clamped an aluminum box section on to the stones to ensure they were in plane with one another:

The central nut was then tightened to fix the stone in place so it wouldn't squirm about any further.

Then the rear post stones were set similarly and clamped up to an aluminum extrusion. Then I could measure the two assemblies to check for parallelism:

The same process for the remaining stones in regards to grouting and aligning. Once done, I felt done, let me tell you.

Here's one side:

The other:

And a view of both, lovely stewartia tree to the left side:

The soon-to-be-relaid granite paving stones will cover the bottom 2" of the granite foundation stones, so their apparent height after the paving is done will be less. I need to return to grout the joints between the sills and flanking stones, and to seal the opening between threaded rods and their corresponding opening in the stones, a minor job I will tackle in about a week's time.

All for today - thanks for your visit to the Carpentry Way. On to post 15.