If you use tatami mats carefully, such as frequently doing maintenance work, they can last for 40 years. However, no matter how carefully you use them, as they are floor material made from soft rush, they deteriorate over time, such as changing color when in direct sunlight, and when stored for long periods in furniture such as cabinets (closets in Japan), becoming uneven in texture. They might also become tattered from being eaten by termites.
In such cases, you can renew your tatami mats. There are three ways to renew them, by flipping over the tatami surface, “ura-gaeshi,” by replacing the tatami surface, “omote-gae,” and lastly, by changing the entire tatami mat, “shin-datami and shintyo.”
☆Renewal method 1: ura-gaeshi
“Ura-gaeshi” is a renewal method in which the surface of the tatami mat is flipped over so that the reverse side now faces up. As tatami mats are weaved in the same way on both sides, they can be used even when flipped over. New tatami mats are green, but as they are exposed to sunlight over many years, they slowly turn yellow. However, as the reverse side of the tatami is not exposed to sunlight, it remains green like a new tatami mat.
“Ura-gaeshi” should be performed roughly every 4~6 years. If the tatami surface is damaged, “ura-gaeshi” might also be done earlier than that. If you have done “ura-gaeshi” once in the past, or the tatami surface is so damaged that the warps in the tatami surface can be seen, then the renewal is done through another method instead of “ura-gaeshi.”
☆Renewal method 2: omote-gae
“Omote-gae” is a method in which the tatami surface is replaced. The tatami surface which had been used up until then is thrown away, but the “tatami-doko” which is in contact with the core of the tatami mat is not thrown away, but reused as it is. If “ura-gaeshi” has been performed once in the past, or the tatami surface is terribly damaged, this method is used.
“Omote-gae” is done roughly every 5~8 years. From immediately after replacement to a few months later, it will smell strongly of soft rush’s unique and pleasant fragrance. The unique effects of tatami mats such as relaxation effects will also be stronger as compared to “ura-gaeshi.”
☆Renewal method 3: shin-datami and shintyo
It is a method in which the tatami surface and tatami-doko are both completely replaced. This is done when the tatami-doko is eaten by termites, has rotted, or has been heavily contaminated by flooding under the floor due to heavy rain. If it is not very contaminated even when wet, it can be reused after being dried for a while. You can get your tatami-doko checked at a tatami mat specialty store for whether it can be reused. Tatami mats are usually replaced with new ones every 20~40 years.