Ninth post in a series describing the design and construction of a replacement gate for the Japanese garden, Tenshin-en, at the Museum of Fine Arts in Boston. First post can be found here. Previous post here.
Big day on site yesterday, as the time had arrived to remove the metal shoes from the existing gate foundation. An inconvenient fact making this process less than a walk in the park was that the shoes were embedded into concrete. To what degree they were embedded was unknown, but this would be revealed soon enough of course.
I brought along a new weapon for this fight, a Stihl Rock Boss:
Also known as the GS461 model, this saw features a 16″ bar and diamond chain. Instead of the usual bar oil lubrication system, you connect a hose to the back of the machine and the chain and bar are water cooled. The front of the saw has a rubber bumper instead of the metal tines seen on a standard saw, and has a couple of rubber feet so it can be placed on a stone surface without issue. One feature I quite liked about the saw was that the fuel filler cap was vertical so the saw could be fueled up without having to be turned on its side like other saws. I couldn’t find one available for rent, so I had to buy it.
Water spews out of the bar and chain area and it doesn’t take long before you find yourself kneeling in a muddy pond. The working position for the horizontal cuts is not always especially comfortable:
The saw cuts well, and can cut through rebar. That said, it will readily, but not easily, cut through vertically-oriented pieces of rebar on a horizontal cut. Sometimes though, there are pieces of rebar inside the concrete which are placed horizontally, and I found that when the saw ran into those it became very slow going indeed. In fact, because the cut is horizontal and I couldn’t get my body weight behind the saw, trying to work through long stretches of metal became incredibly physically taxing. The situation with the metal inside was only revealed after we had finally got the piece off, so when you are cutting all you know is that the saw is making really slow progress and your arms are getting pumped. This morning I feel like I have been in a rugby match.
The saw was really the only option as far as concrete cutting went, as the normal concrete cutting machines would have required a much larger excavation and a bunch of set up time, not to mention the issue of lowering a big machine down into the pit. The Rock Boss seemed the answer, but it turned out to be only a partial one.
Fortunately, my helper Matt brought along his father’s electric jackhammer, and this enabled us to make the necessary, uh, breakthroughs. Every concrete column ended up being cut 60~70% with the Rock Boss and the remainder by jackhammering.
The jackhammer is not a light or delicate tool and pounds the crap out of both the concrete and the operator. That said, I was very thankful to have it, and without Matt’s help I wouldn’t have gotten through all the cutting, chipping, and excavation work yesterday.
As we chipped away to reveal the sculpture within, I discovered that the shoes were welded onto 4 ‘L’-shaped anchor rods, and that the columns were well reinforced with rebar:
You can see in the above picture why the horizontal studs had tended to spin in their holes (as mentioned in the previous post) – not the best type of anchor to use. I thought the shoe attachments and column reinforcements were robustly done, and was impressed with that aspect.
On the right side it took about 3 hours to remove the shoes from the two columns:
Another few hours got us through the left side:
We discovered that the rear post columns had been modified after completion, almost certainly by the people who had placed the granite flagstones. The rear post columns had had their rear metal angle brackets torched off, the threaded studs pounded over bent, and some jack-hammering marks were evident on the backsides of the concrete. This had been done to fit the border stones around the columns. This was a mistake – I’m guessing that whoever had placed the granite was doing so based on a drawing alone and not in adjustment to field condition – – or perhaps they had run out of flagstones and had made the paved area smaller. In any case I explained to museum staff, besides the paving stones not extending far enough, that the rear posts had been too close as it was, so that when the gate doors were opened the edge of the door bumped into the rear post. The doors are supposed to swing clear of the rear posts and tuck in behind them. That’s how I have designed the replacement gate, and it means that the rear post locations will be moved rearward another 5″ or so. I talked with a couple of MFA people yesterday and detailed the issue and they will be engaging in further discussions on this matter.
By 5:30 or so we were done and were both totally wiped out. It was time to go home but – trust me on this – you don’t want to try driving out of Boston at that time of day. Well, it is pretty much the case that you would do well to never have to drive in Boston. It’s not on a grid like New York City and is thus very confusing to navigate, with streets going off in all kinds of direction and nightmarish tunnels everywhere and lots of people driving very fast and close. Even long term residents have told me they are apprehensive to drive anywhere new in the city. We accordingly walked on over to a nearby restaurant and had some dinner. I could tell by the fact that sitting felt mildly painful that today was going to be a sore one. And so it is. The drive home took a couple of hours and traffic was fine. I even got out of downtown without getting lost as per usual.
I think that is the worst of the grunt work over with as far as the foundation goes. The next step is to construct the forms and set them up, and epoxy in some rebar then pour new concrete. That will take place soon enough, but not today.
Thanks for visiting the Carpentry Way. More posts in this series to come soon enough. On to post 10.