[Nyororin]

Take the tatami outside and wipe them down with a diluted vinegar solution (1:3 vinegar:water) then put them in direct sunlight for a few hours. Clean the under-tatami area very well and air it out. After you`ve dried the tatami out thoroughly, put some moisture reducing sheets (you should be able to find them at home centers - if you can, use them to cover the entire area) under the floor and put them back. Look for a carpet or fake tatami-like mat the size of your room, and cover the entire floor.

The odor should be almost, if not totally, gone.

I don`t think that the odor you`re talking about is really the "normal" tatami room scent, but more "damp tatami". Dampness will kill the "good" tatami scent, and leave you with something that does, indeed, smell like wet hay. Brand new tatami do have a strong scent, but it fades very quickly.

When we bought this place, it had been pretty much sealed for 3 months in the dampest months of the year. The smell was VERY strong, and was not considered pleasant by anyone, including Japanese. My husband is a huge fan of い草, but sealed-room tatami is a different smell. We aired the tatami outside in the sun for about three days which made a huge difference. After that, we put down a huge moisture reducing sheet under them... And have not had any more issues with dampness or wet hay odor since.

Febreze can cause discoloring, as can anything baking soda based. Vinegar is best for keeping tatami clean and will help eliminate odor.