So I was right: the sheetrock work is done. It’s time for underlayment, so George came and spent a vigorous half-day installing underlayment in the kitchen. It doesn’t sound like much, but having underlaid several bathrooms, I have vigorous respect for that accomplishment.
Allow me to explain.
Tile–even stone–is fragile stuff, because it’s thin. Say, 3/8 to 5/8 of an inch (roughly a centimeter, for my European readership–hi, Giovanna!). Look at it wrong, it breaks. Therefore, you have to install it in a cozy layer of slightly boingy thinset (mortar with a latex additive), surrounded by determined grout, on a perfectly flat, absolutely solid, staff base, which is affixed within an inch (c. 2cm) of life to the subfloor, which had better be even and bumpless.
Affixing that base is the subject of our tale.
The preferred base is a stiff sheet of concrete backer-board (such as Hardibacker). First you have to schlepp it to the site, which is up 25 steps from the driveway, and it’s heavier than you can imagine, because it is, after all, concrete. Then you have to measure and cut the sheets. You have to stagger all the seams, so that adds a layer of indirection to the measuring and marking task. Cutting it is a royal pain in the ass, wrists, lungs, and goggles, because it is, after all, concrete, which is hard, feisty, and dusty. Next, you have to spread a perfect layer of thinset, which by the way needed to be mixed, set up, and get de-bubbled. Now, you lay down your first sheet of underlayment (which is big, unwieldy, and heavy, because it is, after all, concrete) all at once, so that you don’t scooch all the gook to one end. Now you walk it down, but evenly, so that again you don’t scooch all the gook to one end. Now spread more gook and fit another sheet, and kick, shove, and otherwise persuade it into a nice, tight, square fit. Spread, lay, shove. Spread, lay, shove. Spread, lay, shove.
Got it all in? Squared up? Staggered? Snug? Gooshed down evenly and level? Full coverage? You deserve a beer!
Wait, no! You’re not done yet!
Now you have to fasten it to the subfloor. You have to screw it down, or at least nail it down. I screwed it down, because that’s what Tile Store Guy told me to do, and it’s a pain in the ass (especially when you’re installing it right up under the toekicks of existing cabinetry and don’t have room for both a screwdriver and your hand–yet another argument for ripping out cabinetry and starting over, if you ask me). Even with a cordless screwdriver or even a high-torque drill with screwdriver bit, it’s harder than you can imagine to get the screws through, because it is, after all, say it with me: concrete. Jon has declared nails sufficient. But not so fast, cowboy: you’ve got to put those puppies every six inches in every direction. We’re talking four screws or nails per square foot. Even when you’re nailing, it isn’t trivial. I had no trouble sympathizing with George’s whimper about the nailer being broken and having to pound them in by hand.
It took me a whole day (or was it two?) to underlay a bathroom. George underlaid the whole kitchen, except for two funny-shaped notches, in half a day.