Moisture below this kitchen floor resulted in cupping, which in turn resulted in costly repair work that could have been easily avoided with adequate preparation.

The discoloration on this once beautiful wood floor is a result of mold. It should be noted that the installer neglected to use a moisture vapor retarder.

A common issue is "cupping." As the name implies, this occurs when the wood face of the individual planks takes on a concave appearance. It happens because the bottom of the floor is exposed to moisture while the top dries out and shrinks. Another major problem is "tenting." This comes when excessive moisture penetrates the wood and causes expansion. The planks thus break their bond and rise up ever so slightly-enough to ruin a beautiful floor.

To their credit, manufacturers who serve the installation business have worked to eliminate moisture-related headaches. But they can only go so far. That is one reason why it is important to consider not only the material and application costs, but the warranties. Many are vague and have low permissible values, so read them carefully before the install.

Naturally, you also want to eliminate moisture-related problems before the work starts. First try and identify the source of moisture at the job site. So look around and ask: Is there poor exterior drainage? Is there a need for French drains? How about excessive irrigation? A broken pipe? Or maybe it's a high water table and the lack of a vapor retarder? What about a lack of roof gutters or gutters clogged with leaves? The reality is you can't cut corners on a wood install if you are going to avoid moisture damage.

In any event the industry has worked to tackle this tricky problem with a range of products designed to waterproof the slab. This has led to a great deal of experimentation including these methods:

• Sheet Vinyl. An inexpensive piece of sheet vinyl can be installed before the wood goes down, but this is not always successful. The moisture/alkali present could attack the vinyl bonding agent, resulting in a total loss of bond. In addition, some of the vinyl's lost plasticer into the wood flooring adhesive may cause softening of the adhesive and, again, cause a loss of bond. I don't think any warranties are available for this system.

• Silicates-sodium-potassium. Used as a water protection in all types of installs, the down side risk is long term complications as well as applicator problems. For example spreading it too heavily can cause contamination of the surface as silicates fill the pores of the concrete and create a chemical reaction. Also, since it only penetrates slightly, any excess remains on the surface. Use with caution and check the warranties.

• Two-part epoxy. This is another popular method that has some shortcomings. For one, some epoxies are known to "blush"-that is: they leave an oily surface after cure. To ensure the best bond, the contaminant must be wiped off or dis-bonding will result. In addition, the epoxy itself can be dislodged by water pressure. Also epoxies do not warrant any level of protection. Some manufacturers (if not all) allow their product to be used in situations where the moisture vapor transmission is under 8 pounds using the moisture dome test and under 6 pounds using a moisture meter, others claim to protect up to 12 pounds.

Also, epoxies cannot bridge expansion joints and they require mixing for the hardener to work properly. Most important: Remember that epoxies are highly flammable and potentially dangerous to inhale. In addition to proper ventilation, make certain pilot lights and sources of ignition are turned off.

Urethane moisture vapor retarders

This leads us to a new entry in moisture vapor prevention:

Urethane moisture vapor retarders. Urethanes are a single component and do not contain water. Although initially expensive, they provide the highest degree of protection as vapor transmissions in excess of 12 pounds per 1000 square feet is not uncommon. Other liquid moisture barriers set their max at 6 pounds or 12 pounds.

In addition, urethanes serve as crack suppressants restricting future entry of moisture vapor. Urethanes will bridge cracks up to 1/8 -inch and are VOC compliant.

Yes, it is a major undertaking to ensure that a wood floor is protected from moisture. But remember: This is a type of flooring that will last a lifetime and beyond if you install it right the first time.