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Installing Basic Baths

Depending on what material the bath is made of, it will usually require additional support when it is installed against a wall; this information will be specified in the manufacturer's installation literature. Generally, a 1x4 or 2x4 nailed horizontally at the correct height and absolutely level at the back wall is the basic requirement, though some manufacturers also specify a vertical 2x4 at either corner of the bath.

You'll need to make a decision at this point about whether to install the finish floor before installing the bath or afterward. I prefer to install the floor first because it looks better and adds another protective waterproofing layer above the framing and subfloor, but it does mean that extra care will have to be taken to protect the floor during installation and while finishing the rest of the bathroom walls. Cast-iron baths, which can weigh close to 300 lbs., are particularly unwieldy and will require more than rosin paper to protect the flooring. A protective layer of 1A-in. plywood or Masonite on top of rosin paper might seem like an unnecessary expense, but it will give you peace of mind and is a lot more economical than a big gouge or scratch in the floor. Before laying the rosin paper down, carefully vacuum the floor to pick up scraps of debris that might scratch it. Overlap the seams of the rosin paper, and after laying down the protective sheathing, tape the joints with duct tape to keep debris from falling through the cracks.

Easing the bath into place requires both brute strength and finesse. You'll need at least one other helper for a plastic bath and two or three for a cast-iron bath. A couple of 2x4 runners will make it easier to slide the bath into position and will also help protect the floor. If you've cut one of the protective sections of Masonite to fit the footprint of the bath, then you can just remove that section before installing the bath and pull back the rosin paper. (Don't tear off the rosin paper, though. When the bath is in place, let the rosin paper lap up onto the bath apron to help protect it in the later stages of construction.)

If the bath is fiberglass or acrylic, setting it in a bed of mortar about the consistency of damp sand will help to deaden sound and give the bath a firmer feel under foot. Be sure that the mortar doesn't raise the bath off its front edge or back ledger; if it does, pull the bath out again, remove some of the mortar, and reset the bath. After the bath has been set in place in its framed opening, verify that it is level both front to back and side to side before you attach it to the framing. I like to use a screw gun and galvanized screws rather than a hammer and nails to secure plastic baths to the wall because an errant hammer blow can do a lot of damage to fiberglass and enameled cast iron.

Unless the bath W&O fitting was assembled before the bath was installed, now is the time to do it. There are different types of W&O fittings, and each will require a certain amount of fitting and trimming before it will fit the bath and function properly (the drawings), so follow the manufacturer's installation instructions carefully. After the W&O fitting has been assembled and attached to the installed bath and functions smoothly, the brass tailpiece can be connected to the P-trap and the bath drain, and the bath can be filled with water and checked for leakage.

Installing Whirlpool Baths

While whirlpool tubs are typically bigger, deeper, and heavier than ordinary tubs, their installation is similar, whether they are set against a wall or designed to be set in a deck. This section will discuss the installation of a whirlpool tub in a deck and will highlight the particular plumbing and electrical needs of a jetted tub, but the general installation guidelines are the same for both.

Floor framing under a whirlpool tub—which can weigh over 800 lbs. when loaded with 50 to 60 gallons of water and two adults—should be strong enough to support a load of at least 60 lbs. per square foot. Sometimes sistering on 2x joists to existing framing will provide the needed strength if the existing floor system is inadequate. It may be worthwhile to get the opinion of a structural engineer if you are unsure about the strength of an existing floor system or the integrity of previously cut and notched joists. As a quick test, jump up and down on the floor. If it feels springy, chances are the framing will need to be beefed up.

Tubs can either be set on a raised platform or recessed at floor level. If a tub is recessed, you'll simply need to frame an opening in the floor system by headering off joists in the appropriate location. You will also need to provide support framing beneath the tub, since the edges alone won't be enough to support it.

A tub platform is conventionally framed with 2x4s, making sure that there is easy access for the jet pump (see the drawing below). The height of the platform should be about an inch more than the overall height of the tub so that there is room for shims and mortar underneath when the tub is set in place. If the tub is extra deep, you should think about creating a recess for the tub base to drop into rather than having it sit at floor level because it's difficult for a bather to climb over a tub wall that's much over 2 ft. high, while some tubs are close to 3 ft. deep. Verify the location of the tub drain before making the 12-in. by 12-in. drain cutout, since it may be in the middle of the tub, as well as at either end.

If at all possible, try to apply finish material to the deck and surrounding walls (if any) before dropping in the tub. While it is common to cut in tile to fit around an installed tub, this leaves a vertical joint around the rim of the tub that is vulnerable to water and that is too reliant on caulk for its integrity. It also subjects the tub to considerable job-site wear and tear as workers try to finish off the areas around the tub. I've tried installing the tub proud of the surface, leaving enough room to slide tile underneath, but I haven't been too happy with either the process or the result.

Jetted tubs will require a GFCI-protected dedicated circuit; check with the manufacturer's literature before sizing the circuit. Large tubs should also have 3/4-in. rather than 1/2-in. supplies; otherwise, the tub will take forever to fill up. In some cases, a tub will also need its own hot-water heater to supply the 50 or more gallons of hot water the tub will need per fill.