Preparation for Shower and Tub Surround
Part 1 of a 2-part series on installing tile for a tub or shower surround. Skip to part 2 here. This article deals with the preparations to tile a tub or shower surround in wood frame structures. It follows the actual work performed on a tub surround project in an Arkansas home.
This is Permabase cement board mounted to the studs with 2″ deck screws about every 8″. I cut it with an angle grinder and a 4″ masonry blade. The cutting should be done outside due to the dust it produces. Permabase can be scored and cut, but using a grinder makes a much cleaner and more accurate cut. It’s installed with a ¼” gap above the tub. The joints have been covered with alkali-resistant mesh tape and then filled with thinset. USG mesh tape is sticky on one side, so it can be put in place on it’s own, then skim-coated. Permabase edges are beveled so that the mesh tape and thinset doesn’t make a hump on the wall. The screw holes have also been skimmed to make a flat surface for the liquid waterproofing. The thinset is allowed to dry overnight.
When the walls were framed up for this tub, the opening was a little wider than it needed to be. The studs were also a little out of plumb. I used my table saw and ripped some 1×4′s to the appropriate widths to make the walls plumb, and flush with the lip of the tub. You can see the lighter-colored wood attached to the studs behind the CBU. These furring strips allow the CBU to sit in front of the tub lip, as opposed to bending them out from the framing and making the wall out of plumb in the bottom few inches. As stated before, I used 2″ screws to make sure the screws went through the CBU, the furring strips, and well into the stud. A shorter screw might not have been long enough to reach into the stud.
There is a ¼” gap between the Permabase and tub. This joint is filled with silicone. You don’t want the CBU in contact with the tub or wicking will occur, causing the bottom of the CBU to be saturated. The silicone acts as a “moisture barrier” between the tub and CBU. The silicone needs to be smoothed out so that it doesn’t stand proud of the CBU (raised and uneven) and cause problems later when the tile is put up.
Protect your tub with a tarp or heavy paper. Here my tarp slid off the side into the tub during the demolition and a section of old tile fell and chipped the tub. A tub repair kit can be used to repair damage such as this later, but caution is cheaper.
Laticrete 9235 liquid waterproofing is applied to the CBU joints with a disposable brush, in conjunction with the 6″ wide fabric supplied with 9235. This strengthens the seams and makes a more monolithic waterproofing membrane.
I then used a standard paint roller to completely cover the CBU with 9235, making sure that every square inch of the CBU is covered. This coat dries fairly quickly (2-3 hours) and a second generous coat is applied to ensure adequate coverage. For the second coat, I painted the two corners and down near the tub with a brush, then rolled the field up to about an inch from the ceiling, which is well above the shower head.
This is the first in a 2-part series on shower and tub surrounds. This completes the preparation portion of the project. Please see the next article on installing the tile for this project.