Hot Tubs

Wooden hot tubs enjoyed great popularity in the 1970s and then largely disappeared during the 1980s. In recent years they have made a comeback as people seek simple, natural surroundings and as they discover the economy of wooden hot tubs. Made from any dense hardwood that is resistant to moisture and decomposition (usually redwood), hot tubs are assembled from dozens of vertical boards called staves.

The edges of each stave, which look like a standard 2- by 4-inch (5- by 10-centimeter) plank, are beveled (angled) slightly so that when the staves are assembled edge to edge, the result creates a circle. The bottom of each stave is carved with a groove, called the croze, to accommodate the width of the floorboards. The floor is composed of similar horizontal boards, but with straight edges. One edge of each floorboard has two or more holes, and the other edge has corresponding pegs. This aids in assembly, keeping the floorboards properly aligned, although the pegs provide no actual structural support. The ends of each floorboard are curved slightly, and the center floorboard is the longest, with each succeeding floorboard on either side being slightly shorter so the ultimate result is a circular floor.

The floor is supported by 4- by 4-inch (10- by 10-centimeter) joists. The tub does not actually rest on the staves; rather the floor of the tub rests on the joists. The tub is assembled in the ancient tradition of cooperage (barrel making), with the staves being held together by curved steel bands that are tightened by passing each end through a hoop lug (a hub connector fitting) and secured by nuts screwed down on each threaded end. The tub is made watertight when water is added, swelling the wood and sealing the seams between the staves.

Wood seats are added by fastening bench supports with stainless steel screws. Wood is specially selected and prepared for hot tub construction. Smooth, even, vertical grain is preferred, the best being taken from the heart of the tree where the grain is best and the most tannin is located. Tannic acid makes the wood more impervious to the decomposition effects of heat, water, and chemicals. The wood is then kiln-dried so it i devoid of almost all moisture. Thus, when the finished tub is complete, the wood quickly absorbs moisture and swells for tighter seam sealing.

The woods used for hot tubs differ in various parts of the world depending on their availability and price. It is generally accepted that California redwood is the best hot tub material, but teak, cedar, mahogany, certain oaks, and several exotic rainforest hardwoods are also used. Hot tubs are made in various sizes—the most common unit is 6 feet (2 meters) in diameter by 4 feet (1.2 meters) deep. I have ssembled
and installed tubs up to 10 feet (3 meters) in diameter by 4 feet (1.2 meters) deep with 20 separate jets.

One advantage of using wood for a hot tub is its natural insulation property. Simplicity and blending with the environment of modern gardens and homes are the other. The disadvantages are lack of comfort (you can't mold lounges in a hot tub as you do in a plastic hot tub), the wood maintenance requirements, leaking problems, and bacterial questions. Although a properly maintained wooden hot tub is as clean and safe as a gunite or plastic hot tub, many health and safety codes prohibit wood for commercial or public use because bacteria can be held in organic materials such as wood and transmitted to others.

Installation

RATING: PRO

Installation of the hot tub proceeds along the same lines and requires similar equipment and plumbing as a plastic hot tub. The following guidelines detail the few procedures that are unique to hot tubs.

1. Foundation After you work with the homeowner and/or general contractor to determine the best location for the hot tub, prepare a stable foundation. Hot tub wood needs to breathe, to be surrounded by air. I have been called to installations that were backfilled with sand or dirt, usually for leak problems, and have always discovered extensive wood rot. The tub requires lateral support (side to side), and the most important aspect of the installation is the foundation. Because the weight of the tub, water, and bathers is enormous, do not mount a hot tub on a patio or wooden deck that has not been reinforced.

If you are not using a general contractor, prepare your own foundation. Prepare a level, well-compacted area of ground. Create a form for the concrete using 2- by 4-inch (5- by 10-centimeter) lumber. Excavate the area inside the form to a depth of at least 2 inches (50 centimeters). The completed foundation sits in the ground, rather than on top of it, and will be resistant to shifting or earth movement. Lay 1/2-inch (13-millimeter) rebar in a crossed pattern as shown, creating 1-foot (30-centimeter) squares. Tie the intersections with tie wire to secure the grid. Slide small blocks of wood or brick under the resulting grid to elevate it about 2 inches (50 millimeters) off the ground. Prepare a concrete mix, available at the hardware store, and mix as directed with sand. Pour the form full of concrete, forcing the mixture under and around the rebar grid. Make a screed of a 2 by 4 inches (5 by 10 centimeters) and level the concrete as shown. Allow the foundation to cure for at least 4 days before assembling the tub on it.

An alternate foundation can be made of precast concrete piers, available at masonry supply yards. Set the piers 18 to 24 inches (45 to 60 centimeters) apart in lines so that the tub's joists will rest on the piers. Pier foundations can be used on any solid ground that is not subject to erosion or further compaction.

2. Plumbing Because air must be left around the tub, you can usually set it in place before plumbing it and still have enough room to work. If working in tight quarters, preplumb the tub, as described in the section on hot tub plumbing. In either case, work with the homeowner to determine the location and height of the jets.
Drill holes in the wood, taking care not to cut the retainer bands on the outside of the tub. Jet fittings are installed as described previously, but be sure to use jet throats designed for the thicker walls of a wooden hot tub (the throat is longer; the jet body is the same). Plumb the tub as outlined previously.

3. Air Bubble Rings If an air bubble ring is desired, you must create it from flex PVC. Install an dditional main drain-type fitting near the bottom of the tub. The inside of the fitting is threaded for 1.5 inch (40-millimeter) plumbing. The supply house will have a threaded T fitting that screws into this extra drain fitting, stubbing out to the left and right with ribbed nipples. Lay a circle of 11/2-inch (40- millimeter) flex PVC around the edges of the floor of the tub. The ends of the pipe will fit over the ribbed nipples, creating a ring. Using the guide in the blower section, drill the number and size of holes into the top of the ring. The pipe from the blower to the tub can be glued into the back side of the drain fitting. When air is forced into the ring, the fitting will hold down one side but the other will float. Secure the ring to the floor with a stainless steel hook and a strap made from plastic tubing or some other nonmetallic material. Some air rings in hot tubs are installed under the seats, toward the front edge (the edge at the middle of the tub). Again, the fitting will hold one side, but the ring needs to be secured to the bottom of the seat in at least one other place.

4. Additional Fittings Most hot tubs do not use a skimmer; however, if that is desired, install it as described previously. The other plumbing connections to the equipment will also be the same as with plastic hot tubs. Since hot tubs require frequent draining, many technicians drill a hole in the floor of the tub and install a drain that leads through a 1-inch (25-millimeter) pipe to a hose bib outside the tub. This allows you to connect a garden hose so you can direct the discharge from the tub away from its base. As with plastic hot tubs, it can be plumbed with a three-port valve to alternate between the ring and the jets, or a second blower can be installed.

Break-in

A plastic hot tub can be filled with water and used immediately, but wooden hot tub requires break-in. When you have completed the installation, fill the tub and keep the water running. Water will run through the seams for as long as 24 hours while the wood absorbs water and swells, sealing the seams. If you fill the tub only partially, the seams will close only up to that level, so keeping the tub full is important. Allowing the water to overflow will also moisten the outside of the wood, speeding absorption and swelling. Some tubs will seal in as little as 3 or 4 hours. In any case, keep the water supply flowing until the tub is no longer leaking.

As soon as there is enough water holding in the tub to start circulation, begin to run the pump. Turn the heater on as well, because that will speed the swelling of the wood and the leaching portion of the break-in. For several days, tannic acid and natural wood oils will leach from the timbers, turning the water coffee-colored. The best wood is taken from the heart of the tree where these acids and oils are most abundant, so the time it takes to leach them from the wood is an indi- cation of the quality of the timber in the tub. I have installed some hot tubs that barely discolored the water, indicating the wood contained little protective tannic acid or oils.

Continue to run the circulation 24 hours per day for 2 days. Brush the inside of the tub vigorously once or twice each day to scrub out as much of the acid and oil as possible. There is no way to filter or chemically remove this discoloration, so drain and refill the tub at the end of the second day. It might take two or three such refills before all the discoloration disappears from the tub. Some technicians will tell you various methods to speed this process, including bleaching and soda ash preparations, but believe me, I have tried them all and the only thing that works is patience.

Although you are advised not to use the tub during the break-in, some have done so anyway without suffering any ill effects from the dis- colored water. It doesn't stain and apparently has no detrimental health effect on the skin, but I still ask the customer to stay out of the tub until the water is cleared. Each time you drain the tub, clean the filter and drain as much water from the circulation system as possible to remove all the affected water. When the water is clear, add sanitizer and operate the tub normally.

If leaks persist in a particular seam or part of a seam, take note of the rate of the leak. If it seems to be leaking a little less each day, it might be an imperfection in the wood and will seal in a few days. If the rate of the leak continues unabated, follow the leak repair procedures outlined in the next section.

Repairs

RATING: ADVANCED

Hot tubs are more prone to leaks than other types of vessels, simply because there are so many more places for leaks to develop. In addition to plumbing and through-wall fittings, hot tubs have dozens of vertical seams and the entire length of the croze seam where leaks can develop. In extreme cases, wooden hot tubs can also rot through the entire thickness of the wood itself.

LEAKS IN THE STAVE SEAMS

If leaks develop between the staves, it could mean that the bands need to be tightened. Rarely does a seam leak along its entire vertical length; rather a section of several inches to 1 foot (up to 30 centimeters) will leak along one seam. Tighten the band closest to the level of the leak. If the wood has dried out, fill the tub and allow the wood to reexpand.

If tightening the bands is unsuccessful, the seams can be caulked. Some technicians dry out the wood and apply silicone sealant; others use sealants designed for use on wet surfaces. These measures will work temporarily, but the wood and sealant expand and contract at different rates. This means that in a short time, the repaired area will leak again.

For centuries, builders of wooden ships have caulked seams with
lamb's wool. Because it is organic, it will expand and contract very similarly to wood. Wool contains natural resins and oils, and it will remain impervious to decay for several years. Some technicians recommend twine or other organic materials, but lamb's wool will last the longest.

The best source of lamb's wool is the local grocery store. Mop heads are often made from lamb's wool (be sure you are not buying a synthetic imitation) and provide strands of wool about the right thickness when unbraided. Knitting yarn of pure wool will also work. Repair is a simple matter of pulling out strands of wool from your source material that are thicker than the seam being sealed and forcing the strands

LEAKS IN THE CROZE

The seams between the floorboards rarely leak, although if they do you can caulk them as described previously. Leaks are more likely to be found in the croze. Leaking in the croze can be caused by pressure or wood decomposition. Figure 9-17 shows how a deck can apply pressure to the top of the staves, kicking them outward at the base near the croze and causing separation. The solution is to relieve the pressure and tap the base of the staves back in with a rubber mallet. similar pressure leak can be caused if a band is tightened too much just above the level of the croze. In each of these cases, loosen and reposition the lowest band on the tub so that it wraps around the floor and croze joint. Tighten the band until the staves are replaced securely to the floor.

Pressure leaks are also caused if the bottoms of the staves are resting on the deck, supporting the weight of the tub. Remember, the joists are designed to support the weight of the tub through the floor, not the staves. If the tub has settled for some reason, you can raise it and reposition the joists or piers by emptying the tub and using a car jack to raise it off of the deck. To raise it, apply the jack to a band, not a stave, or you will create more pressure damage. Use extreme caution when jacking a hot tub off the ground. The forces are extremely great, and the jack head is in contact with a small band of metal (which can snap if it is rusted or cracked); and if the tub shifts suddenly, the jack can snap out of place with deadly force. I have jacked many tubs to examine the underside or reset the supports, and I have always succeeded by working slowly and with helpers to steady the tub. You also don't want to take any chances when the tub is raised on a jack by reaching under the tub. Use boards or a telepole to push materials out from under the tub or maneuver new support pieces into place. A £15 telepole is easier to replace than an arm.

If the wood has deteriorated, the croze can be caulked with silicone sealant. Because it is virtually impossible to insert organic materials into the croze, this is the only time when use of a sealant is recommended. Drill a hole in the stave directly behind the floorboard in the vicinity of the leak. Fill the voids with caulk. You might need to drill holes in several staves to stop all the leaks. The hole should be no larger than necessary to accommodate the tip of the caulk tube. You can plug the hole with a short length of wooden dowel of the same diameter as the hole or with more caulk.

LEAKS IN THE FITTINGS

As with other types of hot tubs, hot tubs can leak around jet, drain, or skimmer fittings. Wood is more likely to leak in these areas because the wood expands and contracts with temperature extremes, while plastic does not. Always try to tighten fittings first. A loose fitting is usually the source of the leak. If that fails, follow the techniques already described. As wood ages and deteriorates, the hole around the fitting might enlarge or rot. In this case you might want to fiberglass (as described later) over the face of the fitting where it meets the wood.

LEAKS FROM WOOD DECOMPOSITION

As the tub ages, the wood will begin to decompose. This can be accelerated by poor water chemistry maintenance, but the process is inevitable. I have added another 2 or 3 years to the life of a decaying wooden hot tub by fiberglassing the interior. The entire interior of the tub can be fiberglassed, or you can do just the croze joint or specific staves that are rotting or leaking. The steps are as follows.

1. Drain the Hot Tub Allow it to dry for several days so that there is no surface moisture. If the wood is still moist deep inside, it can dry out by breathing through the exterior, because only the interior surface will be fiberglassed.
2. Sand Use a rough-grain sandpaper (40-grit) to strip off any decomposing wood and expose the best of the hardwood below. The roughness will also aid in creating a mechanical bond for the fiberglass. Wipe out the sanding dust completely, or wash the tub and allow it to dry again.

3. Patch Fiberglass patch kits are sold in most pool supply houses, all boat supply stores, and in many hardware stores. Fiberglass is actually a collective term applied to two distinct parts of a process. iberglass
itself is a cloth woven from yarns of various twist and ply construction into a variety of sheets, strips, tapes, or chopped loose fibers. The fiberglass provides the strength, but by itself is not stiff and will no adhere to a surface. Liquid resin is the other half of the fiberglass process. Resin is a clear or slightly golden liquid that is poured or brushed over the fiberglass fabric. The resin dries hard, providing the bond and stiffener, while the fabric provides the strength. Unless large areas of the hot tub are deteriorated and the structural integrity of an area is in doubt, fiberglass cloth is not needed for this repair. The wood takes the place of the fiberglass cloth, providing the framework onto which the resin is applied. Follow the product preparation directions on the patch kit. Generally, after sanding and cleaning the surface to be fiberglassed, you will mix a two-part resin to paint the surface to be repaired. One part of the resin mixture is resin, while the other part is a catalyst that starts a chemical reaction which leads to hardening. The two cannot be premixed, or the product will set up inside the can. After mixing the resin components, liberally brush the mixture on the area to be patched. As the mixture thickens, it will adhere better to vertical surfaces, so you might want to wait a few minutes before application. In any case, most mixtures will set up within 10 to 15 minutes, so be ready to work quickly. If there is structural support needed, apply a thin coat of resin, then lay up fiberglass sheets or strips. Allow 24 hours' drying time (or as recommended on the particular product you are using), then apply a second coat of resin. Sand lightly between coats to ensure good bonding of each coat. Always mix more resin than you think you will need, to avoid running out in the middle of the job. The first coat will require about twice as much as successive coats because the bare wood will absorb a great deal of resin. When you fiberglass an exposed product such as a surfboard or a piece of furniture, a clear topcoat of finishing resin is also added. But because the patch is inside a hot tub and will not be seen, this clear coat is unnecessary.

4. Fill After allowing adequate drying time for the entire project, refill the hot tub. It will likely leak at the seams that you have not fiberglassed, but the normal swelling should close those leaks. If you have fiberglassed the entire interior, the hot tub is now virtually a plastic hot tub.

Fiberglass hot tubs can be patched and repaired using the same techniques. As with other repair methods, the best way to learn the nuances of preparation and application is to test the products on scrap wood or other materials before applying them at a job site. Working with fiberglass and resins is very easy and a great solution to otherwise impossible leak repairs.

Cleaning and Maintenance

RATING: EASY

Routine service for a wooden hot tub is similar to that for any other body of water, especially concerning chemical balance, vacuuming, skimming, and brushing. There are, however, some important differ- ences about maintaining wood and prolonging its life with proper service methods.

WOOD DECOMPOSITION

Overchlorination will strip lignin out of the wood. Lignin is the white, pulpy cellulose material that binds the organic material of the wood together. The tub will appear to be growing a white fur that will brush off and clog the filter and strainer basket with what appears to be wet newspaper.

The obvious prevention of this decomposition is to lower the doses of chlorine. Because of this problem, I don't use floaters or chlorine tablets in wooden hot tubs. Keep an eye on the filter and pump strainer because they will clog frequently once this decomposition has started.

The solution to this problem is to drain the tub, allow the wood to dry, and sand it down to hard, good wood. Use a coarse-grit paper (#40) to take off the worst of the material, then go back over the surface with a finer grit (#120) to smooth and seal the grain. Refill and reswell the hot tub.

CHEMICAL BALANCE

As the previous discussion indicates, chemical extremes can cause severe problems with wooden hot tubs. Since the wood itself is slightly acidic and the addition of bathers adds more acid, the problem with hot tubs is usually low pH, requiring a regular addition of soda ash. The acidic water will not harm the wood, but remember that it will strip metals from the components of the circulation equipment. Metal stains are not visible on the wood, so there is no early warning sign of such problems. In other words, there is no substitute for regular chemical testing and balancing of hot tub water. Since heat and high bather activity can deplete chlorine residual between service calls, I usually premeasure a small amount of liquid chlorine and ask the customer to add it in the middle of the week. I don't use granular products in hot tubs because they can sink to the bottom before they dissolve, and at full strength will begin wood decomposition. Under no circumstances should you throw a chlorine tablet into the bottom of the tub.

ALGAE AND WOOD

If you discover an algae bloom in a hot tub, superchlorinate the water and brush all the affected surfaces. This process forces sanitizer into grain of the wood where the algae are growing. Drain the hot tub and rinse with fresh water to remove excess chlorine, brushing and rinsing thoroughly. Refill the hot tub and treat the water normally. If you try to treat an algae bloom in a wooden hot tub without draining it, either you will not kill all the algae or the excess chlorine will begin wood decomposition.