Tomobe – North Side Plastering

Throughout this whole process of repairing the north side of our house, something that had been nagging me was the tilt of the building. The level and direction of tilt varies a bit throughout the building, and it’s most pronounced on the north side. So, before closing up the walls I decided to see if I could address the problem. In order to move the building the wedges that lock the nuki to the posts need to be loosened, and that’s much easier to do when things are open. (It would be best to do this with the building completely stripped down to the bare structure). In any case I went for it and got a 1.5ton chain hoist, some heavy duty straps, and tried to see if I could pull the north side wall back into plumb.

I stretched the straps and chain hoist over the longest diagonal distance I could to try and maximize my ability to adjust the tilt.

I gave it everything I could, but despite the fact that I cranked the chain hoist until it was crazy tight, I couldn’t get the building to move at all. I was honestly pretty shocked that nothing moved, not even a tiny bit. But at the same time I felt it was a good indicator of how much strength there is in the stucture itslef. Based on work done by previous carpenters throughout the house I’ve been able to piece together that the building has been slightly tilted for a long time. There are a couple areas that were renovated in the 70’s/80’s and it’s clear that in those areas everything was installed plumb (and has stayed that way) while the surrounding old posts aren’t. If I can’t adjust the tilt, then I at least don’t want to see it get worse, and this test with the chain hoist restored my faith in the strength of the building as is.

(Why the building is tilting is a whole other discussion that could take a while, but my best guess is a combination of earthquakes and warping timbers.)

In anycase, the tilt will have to remain part of the house’s charm and character, but at least now I have a new appreciation for the inherent rigidity of the structure.

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The next task on the list was to repair the bamboo lattice that I had previously removed to deal with the structural work. We’re lucky to have a chunk of forest attached to our property and there’s a nice grove of bamboo growing.

I’ve only worked with bamboo a small amount, and I’ve never been in a position to see it growing up close before, so it’s been really fascinating to watch over the past year. This past spring my wife and I anxiously waited for bamboo shoots to pop up with the hope that we might be able to harvest and eat a few, which we did, and they were delicious.

I had no idea how many shoots we would see, and while at first only a few were visible, soon there were new ones popping up everywhere, and those that we left untouched grew to be nearly two stories tall within just a few weeks. It’s truly amazing how fast bamboo grows. All that is to say, harvesting a few fully grown bamboo for our walls seemed like no problem at all.

Splitting the bamboo was pretty easy, but getting even consistent width strips over a long length definitely required a bit of technique. Little by little I started to get the hang of things.

Once split and cleaned up a bit, I could start filling in the walls. I followed the overall pattern of nailing, weaving and tieing that was evident in the original walls.

Little by little the lattice work started to fill the space.

Since cutting and attaching the bamboo, I’ve learned that it’s best to harvest and use bamboo that has been cut in the winter. Bugs that infest the green bamboo are the main issue. For this first round of wall work we just went with what we had, but for upcoming walls I plan to start harvesting bamboo this coming winter.

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Now onto the main show, mudding!

Earthen plaster is a new thing for me, so working through the various stages of the process has been a huge learning experience. One resource which has been invaluable throughout this project is Emily Reynolds’ book Japan’s Clay Walls.

Below is our mud pit, full of mud that had been soaking in prepartion for the first wall layer. Japanese earthen walls are primarily composed of 3 layers. The first layer contains clay rich earth and straw (arakabe, 荒壁); the second layer is composed of the clay earth, finer straw, and sand (nakanuri, 中塗り); and the final layer is often (but not always) a very thin layer of lime plaster. That’s an overly simplistic explaination, and there are plenty more steps to the process, but these basic layers are what was used on our house.

For the first layer of rough mud (荒土) I primarily reused earth from the old walls that we saved during demolition. I also incorporated a bit of mud from our land which has very clay rich soil, and cut up an old tatami mat for the straw. All of that was mixed together with plenty of water and allowed to sit for several months. In Japan fermenting the mud is a big part of the process. Fermentation helps to break down and soften the straw, and also makes the overall mix much more sticky and easy to work with.

Below you can see the walls after I finished applying the rough layer to the interior side of the walls.

The mud is applied in a thick layer such that it squeezes through the bamboo lattice, “keying” the mud to the lattice. The protruding bits of mud are then lightly smoothed out with the trowel to make the surface a bit more even.

After a couple of weeks that first layer of mud was nearly dry, which you can see below. The color lightened up quite a bit after drying.

I’ve come across conflicting information regarding how much the first side of mud needs to dry before applying the opposite side. Some sources say to wait until the first side is completely dry, while others simply wait for the first application to partially dry and harden up a bit. In our case I applied the first layer of mud and then got busy with other work, so I didn’t get to the second layer until a month later.

Covering up the bamboo with the rough layer of mud was an exciting step. The buildng was starting to look whole once again.

These pictures were taken at the beginning of August during the start of peak summer heat here in Japan. It was pretty intense at moments, but nonetheless it was super satisfying for Kay and I to get the walls closed up. The truly laborious task was mixing the mud, which needed to happen a couple times as we used up all the material we had in the mud pit. Initially I was mixing everything by hand and foot, by pouring the rough materials in the mud pit and then mixing it all together with a hoe and by lumbering around and squishing all the materials together with my feet. Not the easiest task in 90 degree (34c) heat! (Since then I’ve purchased a mixer which has been a godsend).

Here are the walls after drying for a few days. You can see the lighter patches where the mud was starting to dry the fastest, and you can see the cracking of the surface which is normal for the rough layer of plaster with it’s heavy clay content.

Overall I’m way behing in these posts, and work on the house has progress quite a bit beyond what I’ve shared so far. It’s become harder to find the time for writing these days, but there’s no shortage of things I’d like to share. So stay tuned. More posts will come.