Don't Fear the Subfloor

After realizing I would have to do something about the subfloor in my gutted bathroom, I was afraid it meant calling in a carpenter to put down plywood. (I have a persisting fear of power saws ever since I had a near accident about 10 years ago.) But that would really slow down the process so I wanted to see if there was some other option. You never know what kinds of materials are out there if you don't ask, so when I picked up my new tiles at the tile store I did just that. The guys who work there are great, and they showed me a couple different options. I am starting with about 3/4 inch of subfloor, so they recommended that I use 1/2 inch backer board. This is a grey board that comes in 3'x5' sheets, and is sort of crumbly cement compressed between two mesh layers. So I bought 2 of the sheets and a big bag of thinset mortar to use on the joints. The only issue I have to consider is that this will raise the bathroom floor higher than the entryway that leads to it. But I have some ideas for dealing with that.
Some people would probably use the measurements of the room and cut the pieces according to those, and that ought to work fine. But I decided I would rather make a paper pattern to lay out on the backer boards to get my cutting lines. I used 4 big sheets of paper, taping them together where they overlapped on the floor to make the pattern. This made it easy to mark exactly where I needed to make the cuts for the toilet, the heating duct, and to fit in the door frame. I also decided to pull the molding off the inside of the door frame so that I wouldn’t have to make cuts around that in the subfloor and the tile, so that made this part of the project a bit simpler. I cut out the pattern on the lines, placed the 2 boards on the garage floor, and laid the paper pattern on the boards so that it lined up with two of the edges to minimize the cuts. I used a black Sharpie to outline it and scored them with abox-cutter razor knife. Then you should be able to raise the board, bend it at the scored lines, and snap it. I could see it was close to snapping but couldn’t quite get it to go. So I called for backup – my husband came out and re-scored them for me, and he was able to cut them a little deeper than I was. Then they magically broke right along the lines – wow!

For the two holes (toilet and heat duct opening), he helped me a drill holes along the scored lines and then just used a long skinny hand saw to connect the dots. After that, I could do the rest myself. The stuff is pretty crumbly, so it was easy to notch the area for the door frame. In fact, it would be easy to overdo it, so I just did little cuts, and broke out small bits. When I took them into the bathroom to put them down, there was just one little spot that that needed to be trimmed. It was pretty amazing to see it go down on the floor so quickly and neatly.

So the next step was to screw the new layer to the subfloor below. I found a plastic box of green screws especially designed for cement board – about 2” long with a large head to hold the board down tight. The whole idea of this process is to have a surface that is not going to flex or else the grout – or worse, the tile – will crack. I pulled out cordless drill and a phillips head bit. But when I tried to put in the first few, it seemed like they weren’t going all the way in. So back to the hardware store for my new drill with a cord to boost the power quotient. I got one that has an extra handle that helps stabilize the drill and lets me use two hands to apply some extra girl-power pressure. And Whoa, baby, that one drove the screws in so fast I needed to back off a bit. The cement board is kind of granular and it was really easy to go too deep with the screws. But after a couple, I got the hang of the technique and it went really fast. And lickety-split, Bob’s-your-uncle, I was done! It looks so good, I had to keep going back and turning on the light to admire it.