Can you tile over tile? When it works in a Florida house

Yes, you can tile over tile, but only when the old tile is still bonded hard to the floor, the floor is flat, and the extra height still clears your doors, cabinets and appliances. If any of the old tile sounds hollow, is cracked or has lifted, it comes up first, because new tile laid on top inherits every problem underneath it.

In a Florida house the old tile is usually bonded straight to a concrete slab, so the real question is what the slab and the old floor have been doing since they went down. Here is how to tell whether your floor is a candidate, and what changes when it is.

When can you tile over tile?

Three things decide it, and all three have to be true.

• The old tile is fully bonded. Every piece has to be stuck down across its whole back. Tap across the floor with something hard, like the handle of a screwdriver: a bonded tile sounds dull and solid, and a tile that has let go sounds hollow. One hollow tile can be cut out and filled. Hollow patches in several rooms mean the bond is failing, and new tile on top will go with it.
• The floor is flat. New tile follows whatever is under it. A dip, a hump or an edge sitting proud of its neighbour in the old floor shows up again in the new one, and it shows up more with bigger tile.
• The height works. The new tile and the mortar under it sit on top of the old floor, and every door, threshold, cabinet and appliance has to live with that.

What the old floor is telling you

Old tile is a record of what the slab under it has done. Before anyone decides to keep it, it is worth reading.

Cracks that run through several tiles in a line usually follow a crack in the slab. If both sides of the crack sit level and it has not been growing, it can be dealt with. If one side sits higher than the other, the slab is still moving, and new tile over it cracks again along the same line, whatever goes between the two layers.

A row of tile that has pushed up into a ridge, or grout that has crumbled along one line, often means the floor was run tight to the walls with no room to move. Covering that does not fix it. The new floor is locked to the old one, and the same pressure is still there.

Old tile that is not ceramic or porcelain at all is a separate question. Old vinyl floor tile and the glue under it can contain asbestos, and nobody can tell by looking. It gets tested by an accredited professional before anyone breaks it up or decides to bury it.

How much height does tile over tile add?

The full thickness of the new tile, plus the bed of mortar under it. That rarely matters in the middle of a room. It matters at the edges, and these are the places to check before deciding:

• Interior doors, which may need trimming at the bottom to swing over the new floor.
• Sliders and exterior doors, where the track or threshold is fixed and the new floor has to finish below it.
• The dishwasher. It slides in under the counter, and raising the floor in front of it can leave it trapped in its opening.
• The refrigerator, which has to fit between the new floor and the cabinets above it.
• The toilet. The fitting it bolts to sits at the old floor height and has to be brought up to the new one.
• The next room. A wood or vinyl floor in the hall that stays at its old height leaves a step at the doorway, which means a transition strip or a ramped edge.
• Baseboards, which either come off and go back higher or end up looking short.

None of this is unusual, and most of it has an answer. The point is to find it at the measure, not on the day the new tile goes down.

Does new tile stick to old glazed tile?

It can, with the right preparation and the right mortar. A glazed tile face is made to shed dirt and water, which is the opposite of what a bond wants. The old floor is cleaned of soap film, wax and sealer, the glaze is scuffed so the mortar has something to grip, and the mortar is one its maker states is suitable for bonding over existing tile. Getting any of that wrong is how a tile-over-tile floor ends up with new tiles that sound hollow.

The grout joints in the old floor matter too. Deep or wide joints are filled flush first, so the new tile sits on a flat, even bed instead of a grid of shallow trenches.

Can you put tile over tile in a shower or on a wall?

Walls are easier than floors in one way: there is no door to clear. A kitchen backsplash is the common case, and new tile over an old one can work if the old tile is sound. The outlets and switches then sit too deep in the wall and need extenders, and the new edge has to finish cleanly against the counter and the underside of the cabinets.

A shower is different. A shower is a waterproofing assembly with tile on it, and the part that keeps water out of the wall sits behind the old tile, where nobody can see or check it. Tiling over it buries that layer under another one. On the floor, a new layer also raises the shower floor against the drain and the curb, so the fall to the drain has to be rebuilt anyway. For a shower that is due for new tile, taking it back to the waterproofing is usually the honest answer.

The new shower floor still has to grip when it is wet, which is why the slip-rated porcelains in our bathroom tile collection are chosen for that first and their look second.

Pros and cons of tiling over tile

• For: no breaking out the old floor, so less dust, less noise and no demolition and disposal on the quote.
• For: the slab underneath stays undisturbed. Tile bonded hard to a slab can take pieces of the concrete's surface with it when it comes up, and those have to be patched before anything new goes down.
• Against: the floor rises, and every door, threshold and appliance has to work with that.
• Against: the new floor can only be as good as the old one. A problem hidden in the old floor stays hidden until it comes through the new tile.
• Against: it is one more layer for whoever replaces the floor next time to take out.

When does the old tile have to come up?

If tapping finds hollow patches, if a crack has one side higher than the other, if the floor is further out of flat than the new tile can bridge, or if the height will not clear the doors and appliances without a step, the old tile comes up first. The same goes when the new floor is long plank tile or a large format, because a long piece spans more of the floor and asks for a flatter one than small tile does.

Taking it up is real labour, and the debris has to be hauled away, so it belongs on the quote as its own line, along with what happens to the slab after: grinding off the old mortar, filling, and levelling where the straightedge says it is needed. What a tile quote should list covers the other lines worth comparing between two quotes.

Where the bare slab has fine cracks that sit level, an uncoupling membrane between the concrete and the new tile can take up some of that movement. It does not fix a crack that is still moving.

How we decide it for your floor

We check the floor with a straightedge and map the cracks before the tile is ordered, and we'll walk you through what we found and whether the old floor can stay. Because we sell it and we install it, the tile installation crew that reads your floor is the crew that lays the new tile on it, and the crew is ours.

Come to the showroom in Bradenton to see porcelain tile at full size and take samples home, or call (941) 253-0400. When you are ready, send us your plans for a quote, with photos of the floor you have now.