I’m interested in joinery suggestions for the corners of a soaking tub. The tub is 24″ high and retangular in shape. It will be filled the same as a standard tub and there’s no pump or other mechanicals. Possible woods are teak or cedar with a thickness of approx, 1″. Those corners need to withstand the weight of water. I’d rather not use ropes or bands as external reinforcements. Thanks!
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Replies
Through dovetails would be my choice.
Kell
How about using multiple through tennons, pinned and housed. This joint should hold in two dimensions and be watertight. Dovetails will only hold in one dimension without relying on glue.
I agree about dovetals and through m&t... both are workable. What I am curious about is what water will do to opposing grain directions. Will the swelling be even over all jointed surfaces? Or will there be a differential pressure applied thus leading to splits and joint failure? Different pressures would be more an issue w/ thru m&t than dovetails (I think).
There will be a greater tangential swelling than radial, but if your boards are all cut similiarly then there shouldn't be any problem. There may not be any problem anyway.
There is a company that makes rectangular ofuros: http://www.woodentubs.com.
Joseph,
If the longer side of the tub is six feet long it will have a load of 850 pounds on it, before adding people and water sloshing. One inch thick boards will bow under that pressure and neither M&T or dovetails in such thin material would be adequate to hold the corner together. There's a reason why wood tubs are made round if possible, wrapped with steel banding, and are rarely made from wood less than 1 1/2 inches thick. Even small tubs require a fair amount of engineering.
John W.
Edited 6/11/2004 8:06 pm ET by JohnW
use boat building techniques.
Edited 6/11/2004 10:15 pm ET by GeorgeR
No offense, but I don't know what "use boat building techniques" means.
Wood boats are soaking tubs with the water on the outside.
People have lots of techniques for building wood boats. Find one that is suitable to your liking and build a tub.
That has to be one of the dumbest and least helpful responses I have ever read on this forum. The tub he is talking about bears no resemblace whatsoever to a boat and the construction methods for most boats are poorly suited to what he is talking about.
Joseph, If I were familiar with tub building I would make some recommendations but I'm not. I do have a little bit of boatbuilding knowledge and I don't really think that is where you need to look.Tom
Douglasville, GA
Hi Tom,
I've worked on big metal boats, paddled a canoe and driven my car on to Seattle's ferrys ... but I'm not ready to take on learning the complexities of boat building in order to build a tub. Truthfully, traditional boat building doesn't seem the best direction for building a tub. Although the image on one holding the water IN and the other keeping the water OUT is rather amusing,
In summary, the best advice, so far, centers around using thick boards, possibly using band reinforcements and to use either dovetails or thru m&t. I visited the suggested commercial website and a photo of a retangular tub appears to have dadoed corners with visible rows of plugs (covering fasteners?). Alas, no details on corner construction.
It would be great if someone who has built a tub, or owns one, could add a comment.
Joseph
Hi Tom,
I've worked on big metal boats, paddled a canoe and driven my car on to Seattle's ferrys ... but I'm not ready to take on learning the complexities of boat building in order to build a tub. (Wasn't there a nursery rhyme about rowing a tub?) Truthfully, traditional boat building doesn't seem the best direction for building a tub. Although the image on one holding the water IN and the other keeping the water OUT is rather amusing,
In summary, the best advice, so far, centers around using thick boards, possibly using band reinforcements and to use either dovetails or thru m&t. I visited the suggested commercial website and a photo of a retangular tub appears to have dadoed corners with visible rows of plugs (covering fasteners?). Alas, no details on corner construction.
It would be great if someone who has built a tub, or owns one, could add a comment.
Joseph
I guess you don't know much about wood boat building.
I know plenty about boat building but I haven't seen many boat joints that apply to his project. Maybe you could be more specific and cite which joint would work well for the situation since you seem to think it is appropriate.
Would you recommend cold moulding, plank on frame, or maybe batten seam construction. Myabe strip planking the tub is the way to go. Of cours no of these methods would give him the look he ois after and I doubt they would function well as a container to hold water in.
You brought up the boat stuff so why not give him an idea where you are headed with it.
Tom
Douglasville, GA
Edited 6/13/2004 3:40 pm ET by Tom
Tom
A wooden boat basicly consists of wood planking supported by a wood frame. Now depending how much of the tub Joseph wants to leave visible (he'll need steps of some sought to make getting in and out of the tub easy), an external frame could support the water loads. Strong corner frames with diagonal members under the tub should be sufficient reinforcement to allow the corners to use butt joints. From memory, for a 24" deep tub, horizontal loads will be negligible in the top 6 to 8 (maybe even 12) inches, so the last plank could be above the bulk of the external framing. I'd try for a glueless construction with the planks joined edge to edge using tounge and grove joints.
Ian
edited to correct the more obvious (at least to me) spelling errors
Edited 6/14/2004 6:10 am ET by ian
Joseph,
A couple of years ago I watched a Frank Klaus presentation on dovetails at a regional WW show. What I was most curious about was a wooden box he had that held his waterstones....filled with water. I was unable to stick around long enough to see how it was jointed. Perhaps some others here can address how F. Klaus did it. My suspicion is some kind of sliding interlocking joinery....like sliding dovetails...but I don't know for sure..
He did it with standard through dovetails. Then he hammers a small piece of wire into the bottom of the sides, creating a trough from crushed fibers all the way around. After that he planes the "raised portion" on either side of the trough to make it smooth again. He then flips the sides over and nails it to a bottom and fills it with water. When the bottom of the sides get wet, the crused fibers swell creating a gasket all around the bottom and no water leaks out.
For the tub being described in this thread, there is a great deal more stress involved. I still think it can be done.
Kell
Yup, that's eactly how he does it. I watched him build one a few years back.Tom
Douglasville, GA
Kell,
Thanks. BG
Klaus did not use through dovetails for the stone pond, he used tapered sliding dovetails. If you'll remember, there was no glue involved, just a tight tapered fit. The swelling of the wood produced a tight joint at the corners and the 'wood gasket' as mentioned in another post sealed the bottom to the sides.
He does not want to use steel bands. He does not want to pay to buy an engineered version so (I will not do engineering for him.) ...
If he wants to build plank on frame, put a frame on the outside; plank the inside.
If he wants to build plywood, put shear strips on the outside joints. Plywood on the inside.
If he wants to use wood core composite face construction, he can put a reasonable fillet in each corner of flat plates.
Lots of ways to solve the problem.
I looked at the loading. 3300# seems like the most the bottom needs to support. The side loads are rather small compared to the strength of wood joints.
I would use glued up knees on the outside of frames with glued square planking.
Not a good suggestion, George. Boats are built so the forces push the wood together (into compression). Use the same joinery but have the forces on the inside and you're asking for a flood - lol.
I can't think of any wood container that holds liquids that doesn't have some kind of band(s) holding it together. Think wine casks, whiskey barrels, water tanks, ...etc.
Might sound dumb, but you could consider fiberglassing the inside and outside of the tub after it was completed. This is a common practise with canoe building. The grain of the wood shows though and they look very nice. The fiberglass would also add strength to the tub, but I can not venture a guess on how much.
Just my 2 cents,
Dan
"Life is what happens when you are making other plans." - John Lennon
Edited 6/13/2004 11:52 am ET by dan_lott
I looked at the Japanese tubs on the website mentioned earlier, my guess is that the ends have closely spaced threaded rods going through them and that the corners are aligned with a shallow T&G joint with caulking placed in the groove before assembly.
Hope this helps, John W.
Here's my initial plan: Use sliding dovetails for the corners and for the bottom to cut a rabbet wider that the bottom plank. Once the sides are constructed, use silicone as a caulk around the bottom edges. Once this is done, attach reinforement strips in the rest of the rabbets. Silicone is rubbery and long lasting and should provide sufficient gasket-type properties. The reinforement strip will keep the bottom in place and also allow for future removal (if necessary). Regarding wood: My first choice is teak. But I don't have a multi-person work crew to help move a heavy work piece - just me, So I will probably use a tight grained cedar, the traditional wood for the Japanese style soaking tub.
Again, if someone has built a wooden tub, please chime in.
Joseph
Joseph,
I haven't built a tub as you are considering, but I have put together a round hot tub that was made of cedar. On that one, the bottom boards were fully housed in a dado. There was no caulk called for and none required. Since the cedar was dry when assembled it swelled considerably when the tub was filled. Seems like it took about three days to finally stop leaking altogether.
I would not rely on the silicon. There are too many things that can go wrong with a caulked joint.
I wouldn't use silicon even if it did work. It seems to me that one of the beautiful things about a wood soaking tub is its purity and simplicity. To know that there is silicon down there, would turn me off.
Once filled, I think your tub will be water tight. Your dovetail corner will work, don't glue it, you won't need the glue and it just may keep the joint from soaking up water and thus becoming watertight.
You will have to keep this tub filled all the time. Don't let it dry out. If you do, it will never swell to its max again and will always leak.
Unless you have or can get, 24 inch wide boards, use simple t&g joints between boards. Don't use any glue.
How will you assemble this assuming you take my advice and simply dado the bottom? You can't slide the corner dovetails together and install the bottom...... If it were me, I'd still consider using through mortices, housed and pinned. Then you can assemble, it will be watertight, and the look is traditional.
You may want to make a sample: Make a one foot square and 24 inch deep tub. Fill with water and see if it is watertight. The psi will be the same as in the big tub although the total forces against the walls won't be.
Do you know that a traditional ofuro is supposed to be filled to its max before you get in? Way cool....... Of course one must allow for all that water to drain away.
Sorry this was so long. I just want to help. You've been getting some misguided advice in this thread, don't be led astray.
Thanks, good advice. T-G is a good idea for the side pieces. I'm not certain that the tub location can handle the always full business .., there's the humidity factor and the need for fresh hot water at soaking time... I wasn't planning on a heater. I intend to build a secondary tray for over-flow, splashes and general wetness... so it the tub is in a wet/dry cycle and does leak, it will be OK. Either the sliding dovetails or the thru mortises are easy enough to do.
Regarding the joints. I've built lots of furniture, but never anything for water. Hence my questions about differential swelling. If water effects everything about the same, there should be no swollen joint explosions.
I know enough about traditional Japanese joinery to realize what may appear simple is probably subtly complex. Those elegant soaking tubs were made by craftsmen with decades of apprenticeship and later experiences. Also, the wood used for Japanese tubs is most likely difficult to find. I would guess that air dried wood was used for the traditional tubs. I will need to find equivalent woods.
The advice about not letting it dry out is good. Wood that is resrained as it swells takes a compession set, and in truth never swells to the same dimension again when it is reset. With a banded structure, you can drive the bands down to tighten them, but with a square structure, it could be relly difficult to restore the integrity of the joints.
Not al would be lost. You could still caulk the joints, glass the interior, or use a liner.
Good luck.
Michael R.
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