Checking a Soft Bathroom Subfloor Before Tile

On a raised foundation, a soft bathroom floor can be checked from below as well as from above, and on a slab house it cannot. The running record bath remodel riverside inside michigan politics holds shows that many surprises in a Riverside, CA bath remodel sit in the floor, so the notes here start with how a crew tests one before any tile is ordered.

Probing from above

A crew walks the floor slowly, heel first, and listens for the spring and the dull sound that sheathing makes once it has lost its glue. Around the toilet flange, along the tub edge and under the vanity are the usual places. A screwdriver pushed into the plywood at those spots goes in easily where the layers have delaminated. A floor that flexes under a footstep will crack porcelain tile and grout within a season, so softness found now is easier to fix than a cracked floor later.

Looking from below

Many older Riverside houses have a crawlspace. From there the underside of the floor shows brown rings around the drain and the flange, mineral streaks along the joists and a damp smell that points to the leak. A flashlight and a moisture meter do most of the work. Houses on a slab have no underside, so the testing is done from the top, and the floor is usually tile over a mortar bed, which is harder to read until a section is chipped out.

Finding the source of the water

A soft floor always has a reason. The toilet flange may be loose and weeping at the wax ring, the tub drain may leak at its gasket, a supply line may sweat, or a shower pan may have split at the curb. The crew fixes the cause before the floor, otherwise the new sheathing goes wet again. A shut-off valve under the sink that drips a drop at a time can wet a vanity floor for years, and it never shows until the cabinet is pulled.

Patch or replace

A small damp spot that dries hard can sometimes be cut out and patched, with new sheathing tied into the joists on both sides. Wide softness, black staining or rot in the joist itself means the sheathing is replaced across the whole room, down to bare framing. A patch that stops short of sound wood simply moves the weak line a few inches. Screws, not nails, hold new sheathing, and the seams land over framing.

What goes on top afterward

With a sound subfloor, cement board or a bonded membrane can go down under the tile, set in thinset and fastened on a pattern. The floor is flat, dry and stiff before anything decorative arrives. Waterproofing at the walls and the tub line is laid before the tile, and caulk, not grout, closes the joint where the floor meets the tub.