Island Forge: Part 4 – Yakisugi – Crossed Heart Forge

This series of photo essays will document the preparation, construction, and set up of a simple swordsmith style kajiba (鍛冶場, forge building) from the ground up. The main inspiration for aesthetic, form, and technique is the humble Japanese inaka naya (納屋) style of a century ago.

Sorting & Charring

The siding for the walls is yakisugi (焼杉), a traditional charred cypress cladding technique used extensively in Japan. To block uv and increase resistance to decay the surface is fully charred into a layer of charcoal, allowing the heat to penetrate deep into the thin plank (~12mm), changing the whole board and making wood vinegar to repel insects.

As with other Japanese carpentry, the wood is oriented as it was in the tree, with the outside of the tree out and the top of the tree up, and air dried is preferred for exterior cladding. Another school of thought would be to place the kiura outward so the shrinking would tend to tighten the boards to the wall.

Deeply charred surface (left), it can be left as is or brushed off to varying degrees for a different look (right).

Brushing with a stiff fiber brush removes the top layer of soft charcoal and leaves a raised pattern of harder late growth among the eroded softer early growth, in a beautiful dark chocolate colour.

Walls & Doors

The lower parts of the side walls under the windows, the front on either side of the doors, and most of the back wall will be covered with vertical yakisugi. The doors originally made for the previous shop will be reused for this project as well.

South side under the window sill.

Working across the front.

Front complete with reinstalled doors, latch hardware to follow as time allows.

North side under window sill.

Small Portico (屋根のある玄関)

A small roof over the doors serves to prevent water running in behind the doors, and provides a degree more shade and rain protection for the threshold. A siding board from the old workshop was used to form this shelter.

Supports for the small roof are fit into mortises above the doors.

They are notched to carry a cross beam that supports the roof.

The ribs on the top serve to stabilize and strengthen the roof board.

Kasugai Staple Nails

Kasugai (角鎹) are large staple shaped nails that are used to tie joints, often in roof structures. Several are used for the front of the roof beam and other places where joints could loosen over time. The legs are just slightly splayed so the joint is pulled tight as they are driven in. In this case they are forged from 5mm square steel and are about 120mm wide with 35mm legs.

Close up of kasugai staple nail as used in Japanese timber frame.

North side showing the window openings, note the three staple nails visible tying front beams.

The next steps will be to install lath for tsuchikabe.

Timeline

Gathering materials began in Fall 2018, site preparation in December 2018, the lumber was milled in the first week of January 2019, the frame assembled February 5th, and roofed February 7th. Yakisugi siding and tsuchikabe walls installed during March, and interior wall finishing in April. The goal is to have it operational by Summer 2019 minus a few finishing details.

Thanks to all who were involved in one way or another in helping facilitate this project, providing space, time, materials, assistance, advice, and encouragement.