Fixing 2 Loose Bathroom Tiles

When two bathroom tiles come loose, you end up having to deal with everything from where the water is seeping in. Pressing on a single tile with your hand usually won't tell you much. Put a finger in the center of the tile and press slowly — a hollow thud means the mortar underneath has already gone soft, and the tiles next to it are often stuck to each other through the wall. Bathroom tiles usually come up together when you pop them out through the grout line, so the damage spreads sideways. So first check whether it's really two tiles that are loose, or whether the whole row is weak. Run the back of your hand across all the tile surfaces — even within the same row, the back ones can be solid while only the front has gone soft.

The traces of moisture overlap in three ways. Picking out just the obvious ones is enough. One is the possibility that the cement mortar itself never set. Two is the mortar behind the tiles having crumbled in the grout lines. Three is water continuously soaking the mortar because there's no waterproofing layer, or it's already torn. In a wet area like a bathroom, no matter how well bonded a tile is, it will eventually come loose if there's no waterproofing. Once water seeps into the mortar, the cement swells and generates force that pushes the tile up. If you can even see signs that the mortar has soaked and swollen, the repair area isn't the two loose tiles — it has to be widened to the surrounding tiles.

The repair is ultimately about taking the tile off, exposing what's underneath, and bonding it back. It's not hard if you just follow the order. First shut off the water and let everything dry completely. Scrape the mortar down about 5–10mm so the bottom face of the mortar is exposed, then knock it loose with a wire brush until the bottom face is smooth. This is where most people fail. If you just smear something patch-like over it, the hollow thud comes back in two or three months.

The back of the tile has to be clean too. Scrape it with a notched trowel and knock the dust off so the bonding surface can be wetted. If there's greasy hands or fine dust left on it, the adhesive layer only grips on the face. Apply adhesive thinly and evenly to the back of the tile, press it back into place, then cover it with plastic and clamp it down firmly with a towel. If the clamping time isn't long enough, the joint shifts before the adhesive sets and the initial bond breaks. Leave it at least a day, preferably two, without turning the water on. After that, run silicone along the grout — if you let a seam form between the tiles where water can seep through, the same spot will come loose again next time. Last, turn the water on and watch the surrounding mortar for leaks for a bit, and you're done.

If the area under the mortar has already soaked and weakened, it's safer to apply a thin coat of urethane waterproofing, let it dry thoroughly, and then bond. Use tile adhesive or a polymer-cement type for the bonding. Materials with a patch-like character that only hold the surface in place will swell again when they meet moisture, so they don't suit this purpose.

Field knowledge

There's a problem that comes up first whenever you repair tiles. It's hard to find the same tiles you already used, and buying two more of the same tile isn't realistic either. Unless you happen to have spares set aside, that is. For wall tiles, try to buy them as cheaply as you can. You probably don't remember how many come in a box, but it's around eight. If the floor tiles are the same size, they usually cost more. I'd recommend buying something that doesn't look too jarringly different. Get tiles that harmonize with your existing wall tiles — if the mismatch is too obvious, it's better to replace an entire vertical row.

First comes separating the loose or cracked tiles. Wall tiles these days mostly come in two types, and if they're set on a substrate you work them with a dedicated adhesive. If you just smash them with a hammer, the grout will transmit the shock and crack the perfectly good tiles next to them. Before starting, you have to remove the grout so the tiles are separated from their neighbors. Otherwise the impact goes straight through the grout and into the intact tiles and cracks them.

Grout removal is done with a grinder, and the grinder is honestly the tool that causes the most accidents on site. If it catches on a quick-release at high speed, it goes flying. These days hardware stores sell hand tools for scraping out grout, so I'd use those for safety.

When you set the tile, the back — the wall side — will have tile adhesive ridged like waves. You have to clean off any foreign material as thoroughly as possible. Tiles don't bend, so even a tiny bit of debris makes the tile sit crooked. Obviously the grout line won't line up either. Here's the problem: even if you bought tiles of the same size, there will be slight differences, and you have to allow for that.

When you're patching, don't use epoxy. It's expensive. And you're only using a little anyway. Regular silicone is plenty. The color doesn't matter at all. Dab it on the back of the tile in about six spots, like dots. Don't spread it out. Squeeze it on so it sits up thick.

The grout line is what makes or breaks a tile. In other words, the spacing is everything. Shift it even a little and it goes right into your eye. To hold an even gap, split a toothpick you have at home and wedge it on both sides. That creates a natural, consistent gap. If it still doesn't line up, there are other ways — you can fold a piece of paper and slide it in.

Press it gently against the wall. Let the silicone spread into the grooves. Silicone doesn't develop adhesive strength right away. It takes a little time before the bond kicks in. Don't underestimate silicone. Once it cures, it really doesn't come off — it even has elasticity.

You need something to hold it in place temporarily — tape you have lying around the house, stuck to the intact tiles on both sides. That'll hold it. One note: it absolutely won't work if there's any humidity or moisture. Dry it off with a hair dryer if you have to.

And the final grout — this is what you'd use white cement for, and it's quietly annoying. Because putting the grout in is bad enough, but wiping it off is worse. And since you're using silicone anyway, there's nothing wrong with doing the grout with that instead.