How to Waterproof a Shower Pan

Making a shower pan waterproof is one of the most important steps in building a house that will last. If water gets behind the shower, the subflooring and drywall will mold or deteriorate, causing expensive damage and requiring extensive repairs. It is possible to avoid these problems if you properly waterproof the shower pan.

• 1

  Lay the shower liner inside the basin where you will install the shower. Cut a small drain hole into the liner -- using a utility knife -- to allow installation of the drain. Align the cut hole with the drain hole in the subfloor.

• 2

  Nail the shower liner in place on the wall, along the top edges of the liner. Do not nail through the liner and into the floor, as this can cause water to leak. Fold the corner edges over and nail them against the corners of the shower.

• 3

  Cut a sheet of waterproof underlayment membrane -- or basic plastic sheeting -- to fit the interior of the shower, leading from the top edge of the shower liner to the ceiling. Use as few individual pieces of membrane as possible. If you purchase the membrane as a complete upper lining, it may come in one large piece. Place the membrane above the shower liner. Nail the membrane to the walls along the studs, with the bottom edge of the membrane hanging over the inside of the shower liner. The key to waterproofing is making sure the water leaches into the liner rather than behind it and into the wood.

• 4

  Place the shower pan inside the bottom of the shower. Screw it into place.

• 5

  Measure the length and height of the shower walls from the ceiling to the top of the shower pan. Cut cement board to equal these measurements, using a circular saw. Install the cement board pieces inside the shower, using nails.

• 6

  Seal all seams between the shower pan and the cement board, and between the pieces of cement board, using waterproof silicone sealant in a caulk gun. Allow the caulk to dry for 24 hours before installing tile or drywall.