Absolutely not ! This is another common misconception about wood hot tubs. In fact, unlike plastic spas, wooden hot tubs don’t crack, chip, blister, bubble, fade or stain. To clean a hot tub all one has do is drain the water and rinse it out.
If necessary or desired they can be gently scrubbed with a soft brush and a mild bleach/water solution.
Most people leave the outside of a wooden tub natural bare wood. As with any type of wood, over time it will naturally gray from the elements. If you choose to put a finish on the outside of the hot tub, the directions for that finish will need to be followed carefully and most likely reapplied annually.