the Carpentry Way: Gateway (VI)                                                          

Gateway (VI)

    
Yesterday was the day for the removal of the old kabukimon at the Museum of Fine Art in Boston. This is post six in an ongoing thread concerning the design, construction and installation of a gate to replace one at the MFA's Tenshin Garden.

The original gate had lasted only 25 years and was rotting badly. How badly it had rotted, mind you, was a matter that proved to be underestimated even by my own fairly pessimistic assessment.

After some rainy days previous, we had sunshine for this encounter. Once set up, it took only a few minutes to remove the main doors and side door:


As noted, while I knew the gate to be terminally rotten, it exceeded my expectations in that regard:





On the plus side, it was a happy home for many small critters:


There were some persons (not employees of the MFA), who, during a project meeting last year, questioned my assessment of the gate as being in dire need of repair, and suggested that the gate was not in fact in such poor repair as I claimed, that a 'lick of paint' so to speak, a 'little repair work' was all that was needed.  Just a touch up would be fine. The above pictures hopefully illustrate well that reality was otherwise. The Museum was well-justified in replacing this gate before it became a hazard.

And, the worst was yet to come in terms of the actual condition, as revealed by dis-assembly.

The header above the side door had a relief kerf cut into its top surface, which naturally allowed moisture to enter even though there was another beam 6" above it. This beam was, also to my surprise, installed with stub tenons and lag bolts. Using metal fasteners in wood in an outdoor structure just invites rotting, so I could see that this gate was an example of cheap construction originally. The header's lag bolts had corroded to the point where they could not be removed, and I had to saw the beam out with my ryoba.

The next two pics clearly reveal the condition of this piece, which was a relatively well-protected one in the structure:


When you see that even a smallish timber such as this header is boxed-heart, you know that the wood chosen for this project was not especially high quality - at least in those areas where the original builders thought they could cut corners.


I thought it was not the best move, frankly, to place a beam with the relief kerf upwards in an outdoor structure. The kerf could have been placed downwards in a side door header without aesthetic penalty, and if it has to be placed upwards for some reason, then it really must have copper flashing installed on top. Even if the kerf wasn't there, or was on the underside, copper flashing would have been a good idea on any horizontal surface exposed to the weather.

A bigger surprise came next, when I got up onto a ladder to start the dis-assembly of the main cross beam, kabuki, the one piece of the structure with the greatest exposure to the weather. Once up on the ladder, I was astonished to find this principal beam with its relief kerf also upwards, had no copper flashing to protect it:


This picture is really not doing the scene justice, but you get the idea. This open kerf to the sky meant that water had been accumulating in the kerf for years - and inevitably in the joints at the posts on either end of the beam. I could see that at some point in time there had been copper flashing in place, however, like the other bits of copper flashing on the gate, it had been crudely face-nailed through from the top, and the nails had, of course, loosened at some point, allowing the wind to pull the flashing off altogether. No one had noticed that unfortunately - a piece of flashing atop the main beam, well above the plane of view, is/was not the most obvious thing to see of course, so when it went missing it would not have been at all apparent. The issue though, is how it had been attached in the first place. You don't put copper flashing on by face-nailing through the sheet, let me assure you, if a workmanlike outcome is the objective.

As with the header, there is no reason that the relief kerf in the beam could not have been placed on the under surface, most of which rested against a secondary beam, the magusa. The magusa would have concealed almost all of the kerf, and the exposed tenons with a kerfed surface could have had shims patched into the kerf. The original builders, however, chose to orient the kerf up and put the flashing on in a slipshod manner. Furthermore, the magusa itself was lag-bolted from the top in four places and attached to the posts using doubled bolts on each end into the end grain of the beam. Anytime I see lag bolts into end grain I ask myself, what were they thinking? Fastening into end grain is a classic mistake in carpentry.

Of course, the lags were all rusted and a bear to remove. They had gone beyond lag bolting though, actually gluing the magusa to the kabuki(!). I found other places where wood strips had been glued in around the side door opening as well. The glue was failing of course.

Much of the remaining flashing on the gate was just loosely hanging on. Nails and wood. The wood shrinks and swells, the copper sheet expands and contracts with temperature, and the nails get popped up and loose after a while. Many of the flashing fasteners had simply fallen out and were missing.

I had some hope that the main crossbeam might have some salvageable material which could be reused in the new gate, but seeing the situation with the exposed kerf and exposed lag bolt holes in the beam's upper surface, I was immediately disabused of this notion.

I had been thinking to try and carefully extricate the kabuki to save it for reuse, and hopeful that the upper 2/3rds of the main posts might be salvageable. That no longer any sort of possibility, gate dis-assembly was vastly simplified: out came the chainsaw.

We didn't have a crane, so some ropes were rigged up, and the main beam chopped from the post on one end. The opposing post was then cut, and the assembly persuaded over a few inches to the side before it was pulled down, the upper portion of post landing on the top of the rear support post, according to plan:


Now the kerf in the kabuki is clearer to see. My helper Matt is visible in the above picture - I couldn't have accomplished the work near as smoothly and quickly without his help, so I was most grateful for his assistance. 

We then dropped the post chunk-beam remnant to the ground, and I drove the remaining portion of beam out of the intact post with a sledge.

With the beam out, we could get a view of the condition of the wood at the top of the post:


It's a poor joint design anyway, as the mortise is nearly 3/4 of the post thickness.

Once the main beam assembly was down we managed to crack the magusa and kabuki apart, and it didn't take too much longer from there to pull the rest down:


As you can see, there is a temporary chain link fence in place, and the garden will be closed until spring of next year.

I had some hopes of re-using material from the old gate, but I now think at best I might get 1~2% recovery. The poor recovery, along with rather short lifespan, is largely due to poor design detailing and poor carpentry practice during the original install. A lack of maintenance, especially in regards to the piece of flashing that had blown off sometime in the past 25 years, did the rest. I already had seen the shortcomings as a result of the design, but I was a bit surprised to see the short cuts and bad decisions on the carpentry end when I pulled the gate apart. In the tear-down, I got to know the carpenter a bit. This gate, I had been told, was the work of a 'master carpenter'. I guess I would disagree with that characterization, sorry to say.

Sure, maybe the carpenter had to work within budgetary constraints, but that doesn't excuse some of the decisions that were made by the carpentry company (the poor kerf orientations, the use of metal lag bolts instead of proper joinery, the defective flashing installation, the use of metal shoes instead of granite foundation points, etc.).

You've got to know that, as a carpenter, your work will be assessed by those who come along later and fix it or take it apart. While they might never know you, and you might even by dead by that point (this is not often the case given the durability of much which is built these days) they will know you through your work. They will find your mistakes, and see where you covered up an error, or fudged it in some other way, or, see where you did something really well. Your work is your legacy, and the only ones who can really assess it are other carpenters. I'm always trying to learn from older construction, what worked and what didn't, so I can bring these lessons forward.

The other task at hand yesterday, with the gate out of the way, was to poke around and get a handle on how the foundation was detailed. There were no provided as-builts from the initial installation, so the detailing of the concrete under the gate remained speculative at best. Out came the shovels....

The digging was pretty easy, and we found that the foundation supports were the same in each post location: a square concrete column, presumably placed down to below the frost line, and a 3/8" welded metal saddle, with the post shoe welded on top:


The metal shoes are a poor way to connect the timber structure to the earth, as the metal, along with the four through-bolts which tie the posts down to the shoe, a combination which simply promotes rot. All of the posts were rotten on their bottom 24". The main posts, with the openings provided on top by way of the exposed kabuki kerf, were rotten from the ground right up to the beam mortise.

The metal saddle was composed of two angled and gusseted brackets, which connected to one another through the concrete with four threaded rods:


It appears possible that the post shoe and its plate below could be cut off of the angled support brackets, and the bracket removed by undoing the nuts holding it onto the concrete. In this 'best-case' scenario, the metal can all be removed without having to break up the concrete. If the central shoe, however, is also cast into the concrete in the middle portion, then the concrete will need to be demo'ed.

All for now - thanks for coming by the Carpentry Way. On to post 7.