Gateway (47)

Post 47 in an ongoing series describing the design and construction of a kabukimon, a type of Japanese gate. This is a project for the Museum of Fine Arts in Boston.


A balmy -4˚C in the shop today. Feeling a little under the weather, so I didn’t tend to stray too far from the portable heater. Problem is, the heater just about maxes out the available amperage draw on the circuit, so if i use the sliding chop saw, or the bandsaw, the breaker trips and has to be reset. A little tedious after a while.
Started with the finishing up of the rod mortises on the two headers:
Earlier, I managed to stick myself in the thumb with the corner of the chisel, hence the bandaid. Clean cuts heal quickly at least.
The headers were completed with some trimming and chamfering.
Then on to today’s layout and cut out task: the mud sill, or dodai:
The mud sill on the original gate sat in/on the ground, so by the time I pulled it out after 25 years it was mostly soil itself. The new gate features a granite foundation bringing the wooden parts well away from the ground, however I decided to place the mud sill timber into limited contact with the granite, preferring to give the wood as much air circulation as possible on its under surface. So, I designed it with a couple of scallops removed from the underside, leaving only the middle 10″ or so to bear on the granite. This gives the best compromise between carrying the modest load of the panels above, and letting air circulate below. It’s a bit non-standard, however I think these minor modifications will extend the lifespan of the piece quite a bit. It is the only horizontal structural member in close proximity to the ground, so I considered the matter carefully at the design stage.
The cut out occupied most of today, and I managed to complete the work on the mud sill by the end. Here are the three parts, mud sill on the left and then the two headers:

The rightmost header is the one which is on the side door (right) side of the gate.

A closer look at the timber ends from the same vantage point as the previous photo:

The mud sill has a pair of hammerhead tenons on one end, which are captured by the wall post on that side.

The opposite ends of the same three sticks, this time the mud sill is of course on the right side of the photo:

On this end, the mud sill has the same sort of rod tenon attachment as the headers. The difference in the joints from one end of the mud sill to the other are accounted for by the fact that on the connecting wall post end, the wall post itself sits on a plinth about 1″ higher than the granite sill under the mud sill and the connection is right on the bottom of the post, while on the flanking post side the mud sill connects a couple of inches up from the bottom of the flanking post. The differing configurations cause the joinery solutions to vary accordingly. In either case, the joinery is entirely concealed. While the rod mortise on the sill is oriented upwards, the top of the mud sill will be clad with a copper sheet to provide additional protection.

The mud sill will also have a dado to capture the lower ends of the infill panels, however I will leave this portion of the cut out for later on when it comes time to fit the panel assembly to the frame.

Next, a view showing the profile of the mud sill a little better:

I have a little bit of clean up to do yet on the relieved surface, and plan to paint those areas to dampen moisture exchange.

One more, a closer look at the three rod mortises:

That leaves me with two more components in the frame to lay out and cut out, namely the kasagi. I am waiting on some shaper tooling for some profiling work on those two sticks, however I intend to process the joinery tomorrow, and  mill some stock for the doors as well.
That is it for now- thanks for coming by. On to post 48.

10 Replies to “Gateway (47)”

  1. Hi Chris,
    An enormously interesting and inspiring project. Thank you for persevering in updating us all the way through the process.

    A couple of pointers/questions which I am sure you have considered, but nevertheless…:

    Since, as you say, you are making the mud sill on granite non-standard anyway, have you considered shielding the wood from the contact with the stone?

    In log buildings here in Scandinavia, the mud sill is normally placed on a footing of stones – either as pillars or blocks, or as a complete wall. Between the bottom log and the stones a water-dispersing layer is placed. Traditionally tarred flax fibres or tarred sheep's wool. but today tar paper is used (the kind used for roofing), with the tarred side facing down on the granite.
    This gives the wood protection not only against accumulated rain water but also dew forming on the stone.

    Also, you mention that you will chamfer the mud sill and give it support only on the middle 10″. Have you taken into account any slope on the granite block – so that water will run off, and not into the contact zone?


  2. Hi Henrik,

    thanks for the comment and questions.

    The issue of the wood in contact with the stone is one I've considered. The granite does not absorb water significantly nor does it wick moisture, so we are ahead of the game from the outset. Also, the wood will be nowhere near soil, nor can wet soil spashback onto the wood occur anywhere. Plus the wood we are using is naturally rot resistant. so, on all those accounts, the playing field is being tilted in favor of the wood.

    I have contact patches, nevertheless, between wood and the granite in all locations where a post sits on top of a plinth. Those are the areas I am most concerned about, as the end grain of the sticks can more readily absorb moisture. To defeat that somewhat, I will be slightly hollowing a good portion of the bottom of the posts so that the contact patch is diminished, and will be painting those portions with some sort of latex or epoxy paint. Also, some of the posts will be wrapped with copper sheet on the bottom 10″ or so, and this will add a certain anti-microbial aspect from the copper itself.

    The sill itself is not sloped to shed moisture, but is at least chamfered a bit. For sure, a small amount of moisture could sit there, but if there is nothing to absorb it and hold it there, it shouldn't be a problem.

    A modern solution to this issue that I see on newer Japanese buildings with mud sills is to place a layer of grooved plastic (phenolic I think) shims along the foundation, spaced a few feet apart as necessary.

    Tar paper as a barrier is certainly a traditional solution, but not one I've seen used on structures like these. I could consider putting a small piece between the sill's contact area and the granite, or I could continue with my current plan which is to use the epoxy paint. I'm actually less concerned with the contact zone, which is side grain, than I am the scalloped portions immediately adjacent, which have a portion of end grain. Those will be painted. While dew can form on the stone, I do not think it will form directly in those areas of actual contact with wood, and I think the opportunity for moisture from dew to migrate to the wood is greatly minimized overall.

    I'm taking many steps to make the structure more weatherproof, while adhering closely to the appropriate aesthetics for this sort of structure, and at the end of the day there remains the basic fact that a roof is lacking and the bulk of the structure is fully exposed to the weather. Since I cannot clad the entire thing in copper sheet (it is done on some of these gates in Japan though), a certain shortcoming in terms of weatherproofness is inherent to the design in the first place. There is a balance point between cladding with copper and letting the wood be seen that has to be considered. Some decisions in that regard remain to be finalized – should I completely clad the top surfaces of the doors, for example, or just the door stile tops? Obviously, the more cladding the better for weatherproofing, but the appearance must be considered equally.

    I am confident this structure will outlast the original. The original would have lasted much longer if the wood had not been in contact with the soil and the copper flashing had been done properly. I've addressed those issues carefully in the new gate.


  3. It would have been a good idea, now that I think about the matter further, to have made the granite sills with a crown so that they readily shed water. That would have been an improvement, but too late now. I'll file that away in the 'lessons learned' category.

  4. Chris
    I would highly recommend a liquid epoxy to seal endgrain. It soaks in amazingly and 2 or 3 coats are necessary. It degrades in UV, so if exposed to light a coat of paint will help. Paint when the epoxy is tacky and it will glue the paint to itself. Copper or lead make a better bsrrier than tarpaper, because of their anti-fungal properties.

    Looking good !!


  5. Tom,

    thanks for the comment. Great minds think alike I guess. I was thinking to pick something from West System epoxy for treating the bottom of the posts, but I haven't gone shopping yet. I used the term 'epoxy paint' as I'm not sure exactly which product I will go with at this point. seems like the best solution and I am confident it will adhere well to the POC.


  6. Hi Chris,

    Thank you for your detailed answer. It's very informative to learn how a professional, and obviously a dedicated and commited one at that, thinks about these things.

    You are absolutely right – the major areas of concern are those with end grain. On a second note, it is not too difficult to find, e.g in Western Norway, an area of massive precipitation and strong ocean winds, both stave churches and log buildings between 500 and 900 years old and with the majority of the structure in their original condition. Many of these have never been treated. So the basic soundness of the structure, joinery and the basic quality of the timbers seem to be the most important aspects.

    Aging leaves a imprint on wood which we don't find to the same degree in stone structures and my understanding is that also in a Japanese tradition is this fact something to be exploited and cherished, rather than seen as a “defect” in wooden structures. (so keep the copper to a minimum:-))
    It is also heartening to see how you have kept pieces of the original, inferior kiosk, even though it must have presented considerable difficulties vis-a-vis building entirely from new material.

    Thanks again, I will look forward to seeing how this develops.

    Best regards

  7. Will,

    not sure anyone at the MFA is following this at all, so hopefully they will be pleased when they see the final product.

    Thanks for your comment.


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