If all looks good, cover the outside of the frame with a rot-resistant material. Attaching 1-foot-by-5-foot cedar boards to the two-by-four frame will help to strengthen the structure, but you also could use a sustainable option like FSC-certified Ipe wood. Besides having an elegant appearance, it is very strong, rot-resistant, and harvested from eco-managed forests.
To install the tub, mix some mortar and spread it generously on the brick surface below where the tub will sit. Use enough so that the tub, when set in place, will displace some of the mortar, making a molded nest to help support your tub and deaden sound. Place the tub in the frame and stand in it for a few seconds; then remove it from the frame, make sure you’ve spread the right amount of mortar, and adjust accordingly. Apply some silicone caulk under the tub’s lip and return the tub to the frame for final placement. Let it set overnight.
Once everything is in place, use lengths of ABS pipe with a combination of elbows and couplers to connect the drainage pipe to the tub’s drain assembly.
Fill ’Er Up
To make yours the lowest-maintenance tub in town, no underground plumbing is necessary. Simply have a plumber install a hot/cold hose bib on the side of your house. Then you can run a hose to your tub to provide the warm water; it will be useful for other outdoor tasks like washing your dog or car as well. Attach a shut-off valve to the end of your hose, which will allow you to turn the water on and off as you desire without getting out of your tub.
Once your bathtub is finished, you’ll just need to outfit your space. A string of lights, a hook for a towel, a small shelf for a glass of wine, and maybe even an area for the karate kicks you’ll want to do after a long, rejuvenating soak.