Building a round wooden hot tub may seem like a daunting task, but with the right materials and tools, To ensure your round wood hot tub lasts for years to come, it's essential to waterproof and seal it. Use a waterproofing sealant to coat the inside and outside of the tub. it provides are unmatched. But have you ever thought about building your hot tub? Specifically, a round wooden hot tub.