Ofuro (Japanese Bath) Construction Question

[Michael Sobik]

After experiencing Japanese bathing culture, I'm set on having a traditional Japanese Bath. Of course, I need to build it myself!

I'm hoping someone here has some knowledge or insight on constructing an Ofuro. There's a good video on the basic construction here.



at about 1:49 you can see the craftsman laying the bottom on top of the sides. I don't see any joinery. There might be a screw hole by his right hand? You can also see the Hinoki bark being forced into the bottom joint to seal it.

The corners are rabbeted dado joints reinforced with screws, but I can't figure out how the bottom is attached. The bottom planks are arranged across the tub rather than lengthwise, and the four sides sit on top of the bottom. You can clearly see the end grain here (from Bartok Design):

IMGP9463-1024x683.jpg

IMGP9471-1024x683.jpg

And you can see the grain running across the tub here:

IMGP0672-1024x683.jpg

I emailed Bartok, and all they would tell me is the bottom is attached with tongue and groove joints. That doesn't make a lot of sense with regards to expansion. The only thing I can think of is that maybe one short side is joined differently so that is allowed to expand out the end. I think over that width, the bottom would expand and contract substantially. Then again, Japan has a humid climate.

Any ideas on how I can intelligently attach the bottom would be appreciated. Thank you.

Michael

[Osvaldo Cristo]

Wood barrels have their bottom attached with tongue & groove. No glue. I suspect it is the case for that tub.

It is the variation of the wood humidity that brings dimensional variation. If you use the tub reasonably, the wood humidity will stay roughly uniform. You do not need to worry on wood working...

Good luck with your project.

[Joe Cowan]

I recently watched the Totalboat boat build project on youtube. The bottom was 5/4 straightgrained fir and was square edged. He just butted them together and just before putting the boat in the water, he filled the bottom with water with a garden hose and let it set for a hour or so. That caused expansion and such a tight joint, it sealed the bottom. As long as the boat stayed in the water, the bottom stayed tight.

[Michael Sobik]

Thanks for the insight guys. I appreciate it.