Using Sawdust to Stop Leaks in a Wooden Hot Tub

If a wooden hot tub has held water without leaking for some time and then begins to leak, the cause is almost always improper water maintenance and most likely overuse of halogen (chlorine or bromine) sanitizers. Allowing the pH to get too high or too low can also cause leaking in a wooden hot tub. Leaks of this type are usually at the croze (where the staves meet the bottom of the tub). The telltale sign of over-halogenzation is white "fuzz" visible on the inside of the tub.

This fuzz is due to delignification, a process by which the substance inside the individual cells of wood (lignin) is removed, leaving only the cell walls. With the normal use of halogen sanitizers a small amount of delignification is normal. With proper halogen levels, however, this fuzz should require removal with only a light scrubbing from a fiber brush (no sanding or metal brushes) and only once or twice per year. If you have more fuzz then this, you have been using too much halogen.

The level of chlorine or bromine in the tub should never exceed two or three parts per million and should be tested on a daily basis. NEVER, UNDER ANY CIRCUMSTANCES, USE A FLOATING CHEMICAL FEEDER. These devices add halogens to the water regardless of the demand. If you have an in-line halogen feeder in your plumbing, it may be necessary to adjust it often if the tub experiences a varied level of use. If the tub is leaking due to over-halogenization, it may still be possible to eliminate the leak, but unless you also eliminate the cause, the leak will surely return in a short time.

Although rare, other causes of a leaking tub can be a shifting foundation, physical abuse of the vessel, and insect infestation (mostly carpenter ants). Again, before attempting to eliminate the leak, you must eliminate its cause.

There are several products on the market, which purport to stop leaking wooden tubs. Most of these are surface applications. Such materials (usually based on varnish or silicone sealant) are always temporary. The wood is invariably damp when these materials are applied, and so they can be expected to eventually peel off, resulting in a clogged filter and a return of the leak. The "sawdust method" described below is sure to work as good or better than any product designed to stop a leaking tub.

Begin by making a dry paste from the sawdust by adding a small amount of water and kneading it with your hands. This is done to make the sawdust easier to handle and to aid in applying it directly to where it is needed. By looking at the outside of the tub, try to determine where the leaks are. Then, with the tub full of water, try to push this paste into the leaking areas from the inside of the tub. The intention is to have the leaking water draw the paste through the leak, whereupon it should swell and seal the leak.

Before you begin, try to ascertain how badly the tub is leaking. This is usually measured in inches per hour (or inches per day). If the first application of the sawdust paste reduces the amount of water leaking from the tub, then you are on the right track. Several applications of sawdust paste may be necessary to stop the leak. It may also be necessary to repeat the process on a yearly basis, especially if the tub is scrubbed.

Although it is less effective, for widespread leaks you may pour dry sawdust directly into the tub. This method will also obviously require more sawdust to stop a leak. Start with only 6 inches of water in the tub when you add the sawdust. Use about a pound of sawdust to start. Stir as you add water to the tub and fill it almost to the top. Allow the tub to remain filled with water for at least a few hours to permit the sawdust to find its way to the leaks. DO NOT run the pump while the leak is sealing.

When attempting to seal a wooden hot tub using either sawdust method, be sure to keep the vessel full of water so that the water's weight will aid in drawing the sawdust through the leak. After sealing the leak, to remove any excess loose sawdust either drain and refill the tub or run the pump for five minutes then clean the filter. Always check and clean the filter of any sawdust and/or sawdust paste when you are done.