
The floor is clean, and I snapped some chalk where the underlayment will go (highlighted).

Underlayment's been cut. This is just a test, to make sure it all fits. I also decided that
I'd get into trouble later if I left that electrical box that close to the edge, so I put up
another 2x4 there.

A professional would probably have laid that last piece in two sections, but where's the fun
in that? The door was in the way of putting the last piece down, so I removed it, frame and
all. I was going to replace it with one that opened the other direction anyway.
When laying down underlayment, you have to use thinset mortar. To mix the mortar, you need a bucket. (I HAS BUKKET!) Add water, dump in the mix, and stir it up for awhile. To stir it, you use a special paddle that you hook up to a power drill. The guy at the store told me that my cordless drill wouldn't be able to cut it, but when I said I had a corded model, he said I'd be fine.
So I get the bucket, put water in it, dump in the mix, stick the paddle in, and turn on the drill. It goes "urrrrrrr" and doesn't move. I try the cordless, and it works a little better, but started getting really hot and making a funky smell, so I stopped. Fortunately, my neighbor had a drill that was manly enough to mix it up, so I didn't have to throw it all away. Note to self: Buy a manly drill before mixing the mortar to set the tiles. Maybe a Hole Hawg. Yeah, that's the ticket...
Spread the mortar, lay down the underlayment, walk all over it to mash it down, then screw it in.

The final result. Now to get the new tub in. This is gonna be fun...