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How to Hot Mop a Shower Floor

Kimberly Johnson

Hot-mopping is the process of applying hot tar to the floor of a shower pan when installing a shower. Once the thick layer of tar dries, it forms a waterproof seal that prevents leaks from damaging the subfloor under the shower. Hot-mopping is still performed, but there are now premanufactured waterproof liners that perform the same function and are easier to install. Hot-mopping is a sweaty and smelly procedure that requires good air circulation in the home or building.

Hot-mopping involves applying asphalt cement in your shower.
  1. Spread a 1/4-inch thick layer of dry mortar into the shower pan. Use a trowel to compact the mortar and spread it out so that the surface is smooth and even. Create a slight downward pitch toward the center drain as you smooth the grout to allow for proper drainage of water.

  2. Attach a spray attachment onto the end of a garden hose and set the spray to a fine mist. Spray the entire surface of the mortar with a light spray of water until it is thoroughly saturated. Heavy streams of water from the hose will disturb the smooth grout surface.

  3. Start the asphalt kettle and add the amount of plastic asphalt cement recommend by the manufacturer. Set the temperature on the kettle to between 425 and 475 degrees Fahrenheit. Wait for the substance to melt until it is the consistency of paint.

  4. Fill a bucket half full with tar from the liquid asphalt. Dip a brush, or trowel, into the bucket of cement and spread it in an even layer on the lower section of the center drain. Try not to get any cement on the drain section sticking up, as this will be visible after installation.

  5. Apply a thin layer of asphalt over the entire surface of the mortar, using a tar mop. Apply the tar up onto the walls of the shower to cover the blocks at the base of each wall. This is usually only about 10 inches, unless the shower has a seat. If there is a seat, apply the asphalt over the entire seat area as well.

  6. Cut three pieces of 15-lb. perforated felt sheeting to place in the shower pan. Each piece should be large enough to cover the base of the pan.

  7. Place one piece of felt on top of the hot asphalt and walk on top of it to secure it into place. Insert a utility knife into the corner of the pan and run it around the entire perimeter of the pan to trim off excess felt.

  8. Repeat the process of applying alternating layers of asphalt and felt until you have three layers of each. The uppermost layer should be felt.

  9. Cut out the hole for the center drain with a utility knife. Insert a drain cap into the hole to prevent the asphalt from seeping into it before it dries.

  10. Place a 6-inch-wide by 10-inch-long piece of fiberglass webbing into each of the four corners of the shower pan by pressing it into the wall. Position the cloth so that the bottom of it touches the floor of the shower pan.

  11. Apply a top layer of asphalt to the entire floor and the wall area to seal it. Allow the asphalt to dry for at least one hour.