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In this video, This Old House general contractor Tom Silva shows a foolproof way to build a leak-free shower.


1. Wipe down the backerboard surface with a wet sponge.

2. Mix up a batch of mortar and spread it over the backerboard using the smooth side of the trowel.

3. Once the entire wall is covered with mortar, use the notched edge of the trowel to rake the mortar to an even, ridged thickness.

4. Press the waterproof membrane into the wet mortar on the wall.

5. Use a utility knife to cut an X-shaped slit to reveal the shower valve.

6. Rub the smooth edge of the trowel over the membrane to smooth out any wrinkles or trapped air bubbles.

7. Repeat the previous steps to apply waterproof membrane to the remaining shower walls.

8. Spread mortar along the vertical wall corners with a 10-inch-wide drywall knife.

9. Take a 4-inch-wide strip of membrane, crease it vertically down its center, then press it into the wet mortar.

10. Smooth the membrane with the drywall knife. Repeat for the other wall corners.

11. Set the preformed shower pan into position, then mark the center of the floor drain.

12. Remove the shower pan and use an electric drill and 4-inch-diameter hole saw to cut the drain hole into the subfloor.

13. Wipe the subfloor clean with a damp sponge.

14. Spread mortar over the subfloor, and rake it smooth with the notched trowel.

15. Set the preformed shower pan into the wet mortar, then walk across the pan to firmly press it down.

16. Spread mortar onto the walls and shower pan at the inside corners.

17. Press the preformed corner pieces of membrane into the wet mortar. Smooth out any wrinkles with the trowel. Repeat for the other inside corners.

18. Waterproof the seams along the base of the shower walls, where the walls meet the shower pan. Spread mortar, and press in continuous strips of waterproof membrane.

19. Spread mortar around the opening of the drain hole, then press the floor drain into place.

20. Use the notched trowel to spread mortar over the entire shower floor, then press a sheet of waterproof membrane into the wet mortar.

21. Smooth the membrane with the trowel.

22. Install the preformed curb, covering it with mortar and waterproof membrane.

23. Once all the mortar has cured, tiling can commence.