View Full Version : HELP ! How to construct floor in dojo.

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Eivind Bjertnes
12-05-2008, 07:28 AM
Hello everyone.

I am building a dojo on my farm, and need some help in designing the floor. I want a floor that is softer than just tatami on top of concrete.

There will most likely be concrete floor under, but how do I make a "sprung" floor between the concrete and the tatamis?

What is such a floor called in english?

Is is the type of floor also used in gymnasiums for various sports.

Post answer here, or mail me : horse (att) online (dott) no

Timothy WK
12-05-2008, 08:22 AM
It's probably not the same thing, but my old teacher made a "sprung" floor based on Scandanavian sleighs. He described the process [here] (http://www.whiteoakdojo.com/dojofloor.htm).

*I* thought it made a really nice floor, but maybe not everyone would agree. Under foot, it felt solid and "non-squishy", sorta like a wood floor (which I prefer). But unlike most wood floors, it gave ALOT when taking falls... maybe even as much as tatami.

It's kinda hard to compare it to tatami, though. Because it wasn't "squishy" like most pads, it still had a certain "edge" you had to get used to.

12-05-2008, 08:53 AM
We used this method. <http://www.judoinfo.com/tatami.htm>.

12-05-2008, 08:56 AM
It is called a sprung floor in English too - Tim's link looks about right, although you don't necessarily need frames - there is often another layer or two of battens in kind of a criss-cross layer over the first, and then 1/2" ply wood layed over, then another 1/2" plywood layer screwed in to the first (the only metal fasteners). Then tatami laid on top of that. There are also fancy foam blocks you can use instead of the weave of wooden supports. I don't know how much the foam costs or how long it lasts or how well it fares in the cold... I can attest that a well-built sprung floor will last for decades. Have fun!

Eivind Bjertnes
12-05-2008, 09:23 AM
Thank you for quick reply!

I am planning to use standard 4 cm. judo-tatamis over the floor.

I am milling all the lumber for the dojo myself on my Norwood band saw mill from timber that I have harvested myself. I will do most of the construction myself.

Please give some information about manufacturers and type and brand name(s) of the foam used.

Could you make me some drawings please? What kind of wood to use? (I have a lot of good spruce.)


12-05-2008, 10:16 AM
I've trained at a dojo that had a "floating floor" laid over old car tires on their flat. The floor was very comfortable.

12-05-2008, 03:45 PM
I've trained at a dojo that had a "floating floor" laid over old car tires on their flat. The floor was very comfortable.Wow - that's a nice idea! I guess the trick would be find tires of all the same width, but what a great re-use of resources!
I am milling all the lumber for the dojo myself on my Norwood band saw mill from timber that I have harvested myself. I will do most of the construction myself...Could you make me some drawings please? What kind of wood to use? (I have a lot of good spruce.)Cool! Spruce is a great wood to use - I think that European Spruce has an F-value (strength-in-bending) of a little over a thousand, so you should be able to get some good bounce. Since you're milling it yourself, I think milling out the slats at around 4cm by 10cm should give you lumber that's strong enough and flexible enough for a good floor, with 10cm x 10cm blocks at the bottom. I don't know how consistent the thickness you can get on your bandsaw mill is, but 4cm should be pretty even, especially with two people working the mill. I think that anything much thicker than 5cm would, given the span you'd need for spring, amplify the danger of a break at a weak point in the lumber. If you want to PM me the dimensions of the floor you want to build and your e-mail, I'd be happy to make some drawings
with spec and send them to you. :)

Eivind Bjertnes
12-06-2008, 02:06 AM
The lumber I mill is usually accurate to within 1-2 millimetres. (Individual shrinkage might add another mm to that...) The Lumbermate 2000 is an especially accurate bandmill.

But I am also the happy owner of a Logosol PH260 4 head planer-moulder, so uniform lumber is not a problem. The tatami area is planned to be 8 x 15 metres.

The PH260 will be used to make indoor paneling, floorboards for the "social area" as well as the trim and sauna benches. (Sauna is very nice after training...)

12-06-2008, 07:49 PM
We used "2.2pcf polyethylene" foam blocks 4"x4"x3", about 36 per sheet of plywood. Two years ago they were about 32 cents each and shipped in cartons of 300, so shipping to Virginia was around $30 a carton. You glue them on with construction adhesive.

We also added big-assed sheets of 1/4 inch thick foam between the tatame and the top plywood layer.

They came from Wisconsin Foam Products, Inc., whose Account Manager, Tim Lang, was very helpful. <tim@wifoam.com>


Christpher Crandall
12-07-2008, 11:04 AM
Jim's link to the judo floor article pretty decent. However, there is one long-term issue that many (including the judo floor) designs do not take into consideration. Over time, the movement of the floor, mats, wood, students, etc. will cause screws to back out and/or break. Not good if you take a breakfall on a screw that has backed out up under the mat. best bet is to create a floor system that does not use any fasteners. We used 3/4" tongue and groove OSB (or plywood) and foam blocks (like the judo guys) only we made ours from sheet foam and used 3 different sizes. Basically we did the following:
1. Lay out floor so that all joints are staggered. Which means that, depending on your floor size, you will have half/partial sheets on one/both ends of each ply/OSB run.
2. use 2' center spacing for the foam blocks and cut the foam blocks based on where they are in the layout - 6"x6" for blocks in the 'field' of each sheet, 6"x12" blocks to cross the seams of 2 sheets of ply, and 12"x12" blocks wherever there is an intersection of 3 sheets of ply.
3. glue the blocks with contact cement to the plywood sheets. for blocks that straddle a seam, glue the block to the first sheet that goes down and let the other half of the block 'float' under the sheet in the next run.
4. Make sure you allow for expansion with your perimeter frame since the wood will expand and contract due to seasonal temperature/humidity variations (I used 3/4")

I used 1-1/4" closed cell foam to make the blocks (www.resilite.com) and for my foam on top of the floor (my mat is covered with canvas). my perimeter frame is doubled up 2x4s which give the perfect thickness to match with 2 layers of foam and the 3/4' ply thickness. When I designed the floor, I took into account the eventual switch to tatami, so dimensionally, the tatami will fit as is. All I have to do is remove the canvas and foam and then replace with tatami.

Make sure that if you are putting the mat on concrete, you either seal the concrete floor, or lay down a vapor barrier. Otherwise, you will get moisture buildup over time and may end up with a mold /mildew issue on the underside of everything.