If you use cement board, apply cement board tape to the joints, corners, and any other areas where the floor and walls of the shower meet. Another option is to put in green board, a type of drywall formulated to withstand moisture, mold, and mildew. It’s only slightly more expensive than ordinary drywall and can be found at home improvement stores. Even though materials like concrete backing board are designed not to swell, split or mold when they come into contact with moisture, it’s highly recommended that you take the time to treat them with liquid waterproofing to ensure that they’ll last. [2] X Research source
It’s a good idea to extend your waterproofing an inch or so beyond the boundaries of the shower stall itself, just to be on the safe side.
Reinforcing membranes are typically made from tightly-woven fibers. When sandwiched between layers of liquid waterproofing, they’ll provide an additional layer of water-stopping protection. [5] X Research source Leave 2–3 in (5. 1–7. 6 cm) between the membrane and the corners and edges of the shower stall. A little blank space will make it easier to waterproof these areas separately later on.
If you already have a shower head, faucet and knobs picked out, measure them around the base before you cut the slits so you don’t have to make them any bigger than necessary. Do your cutting with an Xacto or craft knife, and place the membrane on a hard, flat surface that you don’t have to worry about scarring up.
Paint-on waterproofing products contain liquid rubber, which both acts as an adhesive for the membrane and a forms a bond that’s too tight for moisture to penetrate. [8] X Research source
You may need to use a liberal amount of waterproofing in order to get the membrane sheet to stick. To help the membrane conform to the corners of the stall, try folding the strips in half widthwise or scoring the backside lightly so that they sit at a 90-degree angle.
Avoid totally covering up the valve and fixture sites. You’ll need to be able to find these later once it comes time to install the finished surface. Brush on the second coat in the opposite direction of the initial coat. For instance, if you used vertical strokes to apply the first coat, use horizontal strokes for the second one. This will help create a better seal.
It may be a good idea to begin your project in the afternoon or evening, then wait until the following day to complete it.
Be sure to arrange the opening for the drain on the same side that the showerhead will be on. Floor trays are included in most shower installation kits. They are typically sold pre-sized and ready to go.
When you’re done, wipe the subflooring with a damp cloth to pick up any sawdust that’s collected nearby.
A handheld brush will be your best bet for applying the waterproofing to the floor.
If the membrane you’re using isn’t large enough to cover the floor in one piece, you can trim and overlap multiple sections to get just the right size. For showers with sliding doors, place a strip around the lip of the stall where you enter. [14] X Research source
Perform at least one one “flood test” when you’re finished to determine whether you’ve waterproofed all parts of the shower stall successfully. Don’t forget to later set the drain, shower head and other fixtures in the openings you left for them.
