Wood Bathtub

Woodworkers are constantly finding new and fancier ways to use their materials to improve our homes and lives. Even so, there is one room of the house which has defied the attention of woodworkers; the bathroom. It seems that bathrooms just aren’t all that conducive to wood, perhaps because of all the water found in them. Water and wood just aren’t a great mix.

Nevertheless, some inroads are being made into this sanctum, as woodworkers find better ways of waterproofing their projects. We see this mostly in vanity countertops, where natural edge wood slabs are finding their way into fancier homes. But the ultimate in putting wood into your bathroom is a wood bathtub.

Wood bathtubs can run upwards of $30,000, making them some of the most expensive bathtubs on the market. You can spend more if you want, buying something carved out of solid crystal or marble. But it is actually possible to make your own wood bathtub, while most of us don’t have the capability of carving a two ton piece of crystal, even if we could find one to carve.

To clarify, there are actually three different things that you can refer to as “wood bathtubs:”

  • A Japanese style deep wood hot tub 
  • A freestanding bathtub made of wood (essentially a modification of the Japanese hot tub, in the shape of an old-fashioned freestanding bath)
  • A laminated hardwood tub

Compared to the laminated hardwood tub, the other two are cheap. You can buy them for a few thousand dollars. You can even find them at your local building materials center. These are “natural wood” tubs, made out of woods which can withstand decay (cedar or rubber-wood) caused by water. The laminated hardwood tubs are made of hardwoods, by only one company, NK Woodworking and Design.

Either the laminated wood tubs or the freestanding tubs found at the home improvement centers are made much like a barrel, with staves which are fitted together and banded to hold them in tight contact. NK woodworking’s bathtubs are made more like a ship, as the founder Nathie Katzoff, got his start in woodworking by learning boat building.

Yet both types of tubs install in your bathroom just like any other freestanding tub would install. All you have to do is set the tub in place, then connect the faucets and drain. It’s actually easier than installing a built-in tub.

Can You Make Your Own?

Since you’re on this website, I assume that you’re asking yourself the same question that I asked myself – can you build your own? Looking at the finished tubs from NK woodworking and Design, I would have to say yes; but it’s going to take a lot of time. While I haven’t seen them build one, I can see how it would have to be built, especially assuming that the artist is working from a background of building boats.

To start with, you’ll need a framework. Any boat I’ve ever seen built starts out with a framework. In this case, the framework won’t become part of the finished tub, but will help in doing the layup and gluing of the tub. To work, it needs to follow the inside contour of the finished tub, keeping in mind that the final dimensions of the inside of your tub will actually be slightly larger than the dimensions of the framework. Once laid up and glued, the final contour will be created by planning and sanding both the interior and exterior of the tub.

I would recommend waxing the outside of your framework, so that the glue from laminating the layers of your tub together can’t stick to it. It would be possible to break the framework, then clean up any scrap from the inside of the tub; but waxing the framework will eliminate the hassle of doing this, saving you time.

While you can make your tub any shape that you want, most bathtubs are built with a slight taper, and with the ends, bottom and corners rounded. This isn’t an absolute requirement, as there are modern tub styles which are squared off. NK woodworking and Designs even has them.

Working from the bottom up, you’ll want to assemble the base first, shaping and gluing the pieces together and setting them in place on your gluing bench. I’d recommend using some sort of template or jig to hold them in place, so as to ensure that they don’t move as you are adding additional layers.

The next piece is the floor of your tub. This is flat, assembled by joining ¾” planks together, much like making a tabletop. I would recommend using dowels or biscuits when assembling this, for added strength. Once laminated, attach it to the base, ensuring that it is properly centered.

With the floor of the tub attached to the base, the easy part of the project is completed. It is now time to start laminating the sides. If your tub is going to have tapered sides, each layer will have to be cut differently, as each layer will be slightly larger than the one below. The layers are cut oversize, with extra material to the outside and the inside (which sits up against your framework to give you a good reference for shaping the tub), leaving that material for final shaping.

As with boat building or laying a hardwood floor, it is necessary to stagger the joints from one layer to another. Even so, it will be easier if you make the long sides with less joints, as they won’t really be necessary. More joints will be needed at the ends, due to the curvature running out of the sides of the boards.

It would be useful to make cardboard patters for each layer as you go, so as to avoid wasting material. The patter can be taken off the layer below, suitably modified to keep it in contact with the framework at all points. Depending on the overall design of your tub, curves, cut out of thin plywood, can be used as patterns for the corners, as the curvature of the corner will stay consistent on some designs.

Two layers of wood planking can be laminated together, and then cut out on the band saw to make the size needed. It will be necessary to verify that the four to six pieces which make up a layer fit snugly together, without any gaps, before installing them to the tub.

Clamping the tub as you build it up is another challenge to be overcome. The secret here is to use wood bridges over the top of the layer being added, with bar clamps going from there to the bottom side of the benchtop. You may need some help clamping, so that you can tighter both sides of the bridge at the same time.

Keep each layer clamped until the glue has a chance to dry. This will, of necessity, make this a very slow project to complete, as it will take longer for the glue to dry, than to cut the next layer of parts to install.

Shaping the Tub

With the glue-up of the tub completed, final shaping will need to be accomplished. You will essentially need to carve the final form of the tub, from the rough glue-up you have made. Layers will need to be blended into each other, as the overall thickness of the tub’s sides is brought down to roughly an inch.

Make sure that you drill the appropriate holes for the faucets and drain, before you get too far along on the shaping process. If you wait until you have the tub shaped, you may end up with chips from a hole saw to deal with. You’re better off doing that earlier in the shaping process, so that you can smooth the edges of those holes as you are shaping and sanding the tub.

There are several different tools which can be used for this shaping process, depending on what you have available in your workshop. Some possibilities include:

  • A chainsaw cutting wheel, mounted to an angle grinder
  • A spokeshave (a bit small, but possible)
  • Wood planes (there are planes with curved soles, which could be used for the inside of the tub)
  • Mallet and chisels 

Most likely, you will find that you will need to use a combination of different tools, as you work over the tub, smoothing it inside and out. Once the final shape is completed, then the tub will need to be sanded, starting with coarse grade paper and gradually moving to finer and finer grades.

wood bathtub, wooden
Wood bathtub, Indo Gemstone

Finishing the Tub

A proper finish must be applied to the tub, in order to protect the wood from water damage. For this, we can take a page right out of the playbook of those who make the natural edge, wood slab countertops. They use a thick coating of epoxy for their finish, because it is both waterproof and durable. It is possible to tint the epoxy, as is done with “river” countertops, but to enjoy the warmth of the wood, you’ll probably want to leave it clear.

Since you will be working without a mold, you’re better off with a heavy-bodied epoxy with a high viscosity, than a thinner epoxy which will leave you with runs in your finish. The heavier-bodied the epoxy is, the faster it will build up a finish. But it will also make bigger, harder to hide runs, if you are not careful.

Having worked with this sort of epoxy on a curved surface like this before, I can tell you that the trick is figuring out how thick a coat you can apply, without the coat starting to sag and run. You’ll also need to keep track of the time, because you don’t want to be trying to use the epoxy once it starts to set up, as the gel-like consistency will tend to leave lumps in your finish.

It is probably better to use an epoxy with a short set time, so that it doesn’t have much time to run. But this will require that you mix your epoxy in small batches; no more than you can work with, in the time you have before it begins to gel. Don’t worry, you can always mix more.

Each coat of finish will need to be sanded lightly to remove any sags and to give it a rough enough surface for the next coat to adhere to. How many total coats you go for will depend on you and how heavy-bodied an epoxy you use. I would recommend a minimum of 20 coats on the inside and at least 10 on the outside.

If you look at the pictures on the NK Woodworking and Design website, it is clear that they use a lot of coats of finish on their tubs, although it is not clear how many total coats they have. Nevertheless, considering the amount of work that it takes to make this sort of a bathtub, you don’t want to short-change yourself at this point. While epoxy is totally waterproof, it is only waterproof if there is an unbroken film of it. Any pinholes in the finish or dents that happen after the tub is installed, will ruin the waterproofing of the tub, giving water access to the wood beneath.

With that in mind, special care should be taken when moving or installing the tub, so as to ensure that the finish doesn’t become damaged. Even the smallest of dents could have dire results on your tub, causing the finish to fail long before it should.

Having never owned a $30,000 bathtub, I really can’t tell you how long the finish will last, before the tub needs to be refinished. You will want to keep an eye on the finish, making sure that it doesn’t become damaged and the wood doesn’t become exposed. Adding additional coats of finish over the existing finish is much easier, if you can manage to do it before there is any damage to the existing finish or the substrate it is on.

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