Installing a ceramic tile floor in an old house
We're thinking of replacing the damaged flooring in our kitchen with tile. It's a more practical surface, especially with children in the house, and a heck of a lot less expensive than the oak we'd have to buy to match the rest of the floor. Our floors are a little bouncy, though. What to do?
Unless you buy salvaged tile, the floor probably won't look old. But ceramic tile is very tough and easy-to-clean so your kids can spill all the juice they want without damaging the floor. And there's so much variety with tile that getting it to blend with an adjacent wood floor should not be difficult.
Another option is Mexican Saltillo tile, which are unglazed pavers made from clay. They're not as durable as ceramic tile but they have a warm, rustic look. (Yes, I know, they're really meant for a Southwestern adobe, not a four-square in Vermont. Yet they have a pleasantly rustic look no matter where you live!)
But the bounce in your floor is going to be a problem.
Tile will crack if it flexes too much
One advantage of a wood floor is its resilience. It bends and flexes right along with that under-sized floor framing you have.
Tile won't do that.
Try bouncing on your toes in the middle of the room. If the china cabinet wobbles enough to rattle your collection of sherry glasses, the tile floor is probably going to fail. Either the tile will crack or the grout between the tile will crack. Either way, it won't work.
For ceramic tile to survive on a floor, the flex of your floor should be no greater than an inch of up and down movement for every 360 inches of width of the room This means that if a room is 12 feet wide, a little less than 1/2 in. of sag is okay.
If you're intending to use stone tile cut that in half to an 1/720.
First, toughen up the floor with more underlayment
Tile should be set over a subfloor and underlayment that together are at least 1 1/8 inches thick. In an old house, you'll almost certainly need to add a layer of plywood to the plank subfloor.
Glue and screw this underlayment in place. Use a construction adhesive like PL400 and real wood screws. (Drywall screws are great for drywall but they're also very brittle.) Place screws every six inches.
This new layer of material should take a lot of bounce out of the floor all by itself. If not, you'll have to reinforce the floor framing itself.
There are several ways to accomplish that.
One is to add intermediate blocking between joists. Blocks are just short pieces of dimensional lumber cut so they fit snugly between joists. Run a line of blocking at mid-span.
You'll get better results by gluing and screwing a layer of 1/2-in. plywood to the bottom of the floor joists. This creates a diaphragm that should stiffen the floor considerably.
If all else fails, you can add a post at mid-span. This isn't always practical, of course, but it can be a good solution when the offending floor is over a basement and you can stand looking at yet one more post.
New membranes also can help
Some tile installers now use an uncoupling membrane between the tile and subfloor. It's designed to isolate the tile from whatever movement there is in the floor below and thus prevent cracks.
The most common is called Ditra-Mat made by the Schluter Co. (www.schluter.com).
It's bonded to the subfloor with latex-modified thinset. You can set the tile with less expensive dry-set mortar.
The membrane isn't cheap. But it's cheaper than having to rip up a tile floor that's beginning to look like that crackle finish on grandma's ancient blanket chest.
An accomplished woodworker and carpenter, Scott Gibson is the former editor of Fine Woodworking magazine, and a former editor at Today's Homeowner and Fine Homebuilding magazines. He also is former managing editor of the Kennebec Journal, a daily newspaper in Maine.