Full Bathroom Reno Day 8: How to Install Cement Board and Waterproof Seams

On day 7 we left off with the plumbing completed, the tub attached to the wall, and one sheet of cement board installed.
 

 

On day 8, we started off by installing the rest of the cement board on the tub/shower surround. We used the same method to cut the cement board as before. First we measured it,

then we marked where it needed to be cut,

and then scored it multiple times with a utility knife.

Once it had been scored well, Jake bumped it with his fist,

 

and then wiggled it back and forth to complete the cut.

 



After this, he cut the remaining bottom portion with the utility knife. Then it was ready to use.

We installed these just as we did with the first sheet, using screws every 6-8" apart, being careful not to get within 1/2" of the edge, for risk of splitting it. We also left a 1/8-1/4" gap around the edges, because cement board will expand and contract and it needs room to do so. Otherwise, the board or tile on top could break.

 

 

Once the cement boards were up, we needed to begin the waterproofing process. We mixed up thinset according to the package instructions with a mixing attachment on our drill, to use to apply a waterproof band.

 

 

 

Then we applied the thinset over the seams in the cement board with a putty knife, making sure to get at least a 9 inch spread, 5 inches for the waterproof band and 2 inches on either side, per the directions.

 

The next part is a two person job- I held the waterproof tape as Jake rolled it out over the seam. Then, he smoothed it and secured it by pressing it firmly in and making sure it was adhered securely. We did this on all 3 horizontal seams first.

We followed the same method in the corners.

 

Then we went back over all of the seams again with thinset to further secure the edges, and smoothed it out.

We repeated this over all of the seams and waterproof bands. I should note, before doing any of this, you should properly cover the bathtub to catch any drips. We used a furniture blanket and blue tape.

The thinset has to dry for 24 hours, and it was about midnight in these shots, so that's where we leave off for today!