Stabilize a Floor for Tile
Subfloors for tile installations require a little more attention to detail than other flooring materials. A floor might be solidly constructed and adequately supported but still have a degree of “bounce” or vibration when people walk across the room. This is usually not a major problem with resilient flooring, carpet or even some tongue-and-groove systems. Stability and rigidity should be addressed, however, if you plan to install a tile floor, because any minor amount of deflection in the subfloor could result in cracks or damage to the brittle material.
That was the problem faced by pro remodeler Ritchie Hamilton during a recent flooring job. Over time the house had settled and the floor joists had sagged. Not only did this result in a noticeable dip in what should be a flat surface, but the floor lost rigidity, and the surface would slightly bend and bow when you jumped up and down on it. Installing mortared and grouted floor tile over the unstable floor would invite cracked grout lines, loosened tiles, and maybe even broken tiles.
If you can gain access beneath the subfloor, you can construct a perpendicular beam with piers to level the joists and stabilize the framing with additional support that connects to the ground. The beam serves two purposes. First, it bridges across the bottom of the joists so they can all be leveled to the same height to reduce sag. Second, if it’s located midway through the span of the joists, the beam essentially halves the length of the unsupported framing, which takes some of the flex out of the flooring. That was the solution that Ritchie chose to strengthen the subfloor and ensure a long-lasting tile floor installation.
Here’s how it went.
The surface of the existing floor was covered in resilient flooring. A little jumping around was all it took to determine the subfloor was in no shape for tile in its current condition.
Ritchie’s first step was to level some precast concrete pier footings laid in a row perpendicular to the floor joists he planned to support.
After locating the joist that sagged lowest in the crawlspace, we attached a 4x post to its underside with a metal construction tie. In this case the beam was a 4×4, but a 4×6 would work even better.
Ritchie placed a bottle-jack on the footing beneath the lowest joist and used a 2×4 extension block to slowly raise the joist and beam. As the sagging joist goes higher, the gap shrinks between the beam and the bottom of the neighboring joists.
Be sure to keep the jack and wood block perfectly plumb, otherwise the tension on the block will cause it to shoot dangerously out of the jack.