About the Tatami
One tends to think of tatami as the traditional flooring in Japanese architecture. And so it is - today. The traditional flooring used throughout Japan's history until late in period was simply wood. No rugs. No tiles. No piles of straw.
During the Heian and Kamakura Periods, tatami were seats and bedding; it was not until the Muromachi Period that they first began to be used for general flooring, but even then only the homes of the wealthiest aristocrats. By the year 1500, homes of many members of the aristocracy - civil and military - were in general floored over with the mats.
The first tatami were for bedding, being softer than the floor, and conveniently sized for one person (or two very good friends...) to sleep on.
The sizes of tatami today vary slightly depending on the region of Japan in which they are produced, but the standard is approximately 3 x 6 feet (90 x 180 cm), fairly close to the Period size. Today, room size in Japan is spoken of in terms of a number of jō (mats) that will fit inside it. Given their standard size, the most common rooms are 4½, 6 and 8-mat, or 9 feet square, 9 x 12 feet and 12 x 12 feet respectively. Anything above 8 mats is considered huge.
One or more tatami could be used as a dais, as shown in the opening scene of Kurosawa's 1980 film Kagemusha. Even in later architectural styles which incorporated a raised dais in the floor plan, a pile of tatami could be used to produce a sort of super-dais.
The top surface of the tatami is a smoothly woven straw mat over a thick and rougher finished foundation. Tatami are green when new, but rapidly fade to a golden brown. The smell of fresh tatami is wonderful and beats the smell of a new car hands down. The long sides of the mat are bound with strips of cloth, often brocade. In the Heian Period, the colour and pattern of the binding were determined by the relative rank and position of the owner, but by the late Kamakura Period, such distinctions were lost.
The one rule - observed even today - was that when the floor was covered with tatami (as opposed to isolated tatami seats, beddings or a dais), all the strips would have to be cut from the same cloth. On sleeping mats or seating, such uniformity does not seem to have been an issue.The origin of the name comes from the verb “tatamu”, which means to fold or to layer, implying that the earliest tatami were thin, and folded up or where stacked out of the way when not in use. In this, they are much like modern goza, or tatami surface matting, today often used as ersatz tatami flooring in Japanese restaurants. How to tell the difference? True tatami, at 2½ inches thick, are actually very soft and springy.
Their best use within the SCA is as small seats, bed platforms, or even as a dais for holding court al fresco. In outdoor seppuku scenes in films, we are often given the particulars: a white groundcloth is laid out (though for a court any color but white or black would be preferable), and two or three tatami are stacked in the middle. This would be fine for one person, sitting in the middle.
Several mats laid side by side and stacked could support two and perhaps a herald. Good backing would be jinmaku, or camp curtains.
First you have to decide what you need. Here we assume a standard 6 x 3 foot model, about an inch thick. If you are making these specifically for use as a dais, you might want to cheat even more and make it thicker with the addition of 2 x 4 around the edges and as a framework supporting it below. You can make them lighter by using ⅜ or ½ plywood and supporting it underneath with a framework of 1 x 2's.
¼ inch plywood sheet, 3 x 6 feet
Soft surface (e.g.: heavy corrugated cardboard, ¼ inch dense closed cell foam, etc.) 3 x 6 feet.
Goza matting, 3 feet wide and long enough to wrap over the long ends and reach a few inches to the underside of the wood base. (Note: Thanks to martial arts group that use these for their practice, you can get goza, aka tatami omote, from places like Nihonzashi. Look for tatami targets.)
2 strips of brocade or coloured cloth about 9 inches wide and as long as the matting.
Place the brocade good sided down on the matting edges aligning. Sew the brocade down 1-1½ inches parallel to the edge and turn over. Repeat for the other long edge.
Lay the soft surface on the tatami platform.
Lay the goza matting over the platform with the ends extending over the head and foot. Turn over, pull the matting tight over the head and to the under surface, and staple or tack down. Repeat for the foot.
Pull the brocade down and fasten similarly to the matting with staples or tacks, left and right.
Finish brocade edges at corners like hospital corners on a bed.
Turn it over and stand on it. Feels good, huh?
And please don't say "tatami mat". Do you say "station wagon car"?
An 18 x 18 inch "cushion" called a shitone was the original seat cushion used by the Heian nobility. It is made the same way as the tatami here, but the fabric is used on all four sides. Make a few while you're at it.