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Fiberglass, tile, marble, granite and solid surface materials are among the most popular finishes for the walls that surround a tub or shower. Although taste and budget usually dictate the choice of material, any one of these products can do a good job of preventing water damage to wall and floor framing, providing it is installed and maintained properly.

However, good finish material simply isn't enough in the war against water damage. Most materials require a waterproofing base to protect the framing. Mortar, mortarboard, building paper, hot tar, a single-ply synthetic rubber barrier or a combination of these materials are used to create a waterproof barrier.

Aside from the finish material and its waterproofing base, caulking is the single most important element in preventing water from making its way into places where it doesn't belong. If we had a nickel for every spongy floor or water-soaked wall that could have been prevented with a simple bead of caulk, we could fill a bathtub with coins.

A bead of caulk is used at joints where the shower or tub wall material meets the top of the tub or shower pan and at inside corners where walls meet. Caulk is a gluelike flexible material that, if the right type, will stick to virtually anything. It expands and contracts in harmony with the surrounding material to provide a strong waterproof seal.

Like painting, the key to a successful caulking job is preparation. The joint must be clean and dry. Moreover, any existing caulk should be removed.

Start with a sharp, single-edged razor blade in a holder or a utility knife to cut the caulking free. Keep the razor angled as low as possible to avoid damaging the surface of the tub. This is especially important when working around fiberglass or acrylic tubs or shower pans. With the majority of the old caulk removed, use caulking dissolver to soften what remains. Use the single-edged razor to finish the job.

Once the caulk has been completely removed, the joint should be thoroughly cleaned. Mildew can be removed with a solution consisting of one-third cup powdered laundry detergent, 1 quart liquid chlorine bleach and three quarts of warm water. Allow the solution to work for 10 minutes or so, then rinse thoroughly and towel dry. Next, wipe the joint down with denatured alcohol and allow it to dry.

The two most popular types of caulking for tub and shower enclosures are silicone and latex. Of the two, silicone is best for sealing metal, glass, tile and other smooth, nonporous surfaces. It is the most flexible and shrinks the least. Best of all silicone is especially well suited for sealing dissimilar materials.

Most people, however, prefer to use latex (or acrylic) caulking. Latex is water-soluble and that makes it easy to use and easy to clean up after. Latex caulk is best for use with highly porous surfaces. Since latex caulk is used on both inside and outside surfaces, it is available in an interior and an exterior grade. The exterior grade is a bit more dense and therefore slightly more expensive. Exterior grade latex can be used inside, but interior grade cannot be used outside. So, be careful to choose the proper type at buying time.

For the best of both worlds, a latex caulk with silicone is a popular alternative.

When caulking, remember that the width of the bead will be about 25 percent to 30 percent wider than the diameter of the hole that you cut in the end of the caulking tube. Thus, be certain to start with a small hole at first. Run a test bead on a scrap of wood. Enlarge the hole at the end of the tube with a utility knife -- a little at a time -- until the desired bead width is achieved. It is important that caulking touch on three sides (bottom and two sides) of the groove being caulked. Each surface helps to hold the caulking in place.

Caulking requires two important tools: 1) your finger and 2) lots of paper towels or a damp sponge. (Your finger, because it is flexible and can be formed to fit almost any shape or surface and the paper towels or damp sponge so you can frequently clean your finger and the joint where the caulk is being applied.)

After wiping the joint with denatured alcohol, apply one continuous course of masking tape to either side of the joint. The edge of the tape should be held approximately one sixteenth of an inch from the center of the joint. Tip: use blue painter's tape instead of conventional masking tape because it has less adhesive and is easier to remove.

With the tape in place, caulk away, removing the excess as discussed earlier. Peel back the tape -- pulling away from the joint -- and, voila, a perfect joint every time.