we will ship with every tub a complimentary hygrometer to monitor the humidity in the bathroom and prevent damage to the wood.

A client reported a (superficial) crack to an asnaro tub we shipped earlier this year.

The ofuro was made with well dried ao-hiba and something like this does not happen unless the wood is really very dehydrated.

We asked the client to check the relative humidity in the room and report to us (3 readings at morning - noon - evening)
Before thinking of a way to repair the crack, we should quickly isolate and eliminate the problem otherwise the tub may suffer more damage.

1) Is there a heater or radiant floor in the bathroom? If yes, it should be kept off while the tub is empty.

2) Is there central air conditioning? Often these systems have dehumidifiers in line. Again, the AC should not be used in the bath area while the tub is empty.

3) Is the ofuro seldom used? (should be used 2, 3 or more times a week!)

4) Keeping some water inside may preserve the tub for periods when it is not used. Anyway, it is important to either fill the tub to the top, or keep few inches of water and
a cover on the tub so that the humidity can reach also the area close to the edge.

5) If the tub is left unused for extended periods and the AC/heating is very powerful, the option of keeping some water inside and a cover on top may not be sufficient as the dry environment would attack the outside of the tub. In this case I recommend to wrap the tub also on the outside (as much as possible) in a similarly to the way it was delivered.

Wishing that this would never happen again, from now on, we will include with our bathtubs a complimentary hygrometer.
We recommend to keep it in the bathroom and be sure that the humidity is above 55-60%. If the environment is very dry, and the tub is seldom used there is the chance that the wood may crack.