why cant i lay floor tiles straight on to the floorboards,? rather than putting 18m ply down?

Answer 1

Floorboards flex when weight is put on them (like walking or if you move something across the floor). It might be slight, but this is enough to cause cracking in the grout and maybe even the tiles themselves.

When I had my floors done with tile, the installers first screwed down hardy-backer (1/2-inch cement-based panels). Then they put down a layer of a plastic-based compound that was like a cement slurry, which they applied and spread around to make the floor completely level. Next, they put down a layer of mastic and applied a slipsheet (layer of plasticized paper). This allows thermal expansion and contraction of the sub floor, without affecting the tiles or grout. Finally, they put down another layer of mastic and set the tiles.

The entire floor construction layer, from the sub floor to the top of the tiles, is about an inch thick. So, it will easily last the lifetime of the house without cracking or separating.

Answer 2

It's the floor rigidity that's important. If the floorboards are in great shape and put down really well you could probably get away with it. But why chance it? If you want a really nice job put the ply down.

Answer 3

Individual floor boards will move more than you think. That will telegraph through the tiles and they will become loose or detached. You will end up with a crappy job.

Answer 4

They will never stay level they will constantly pull apart and shift on you. If your floorboards but against each other and are level you might have a chance but most are not. If you believe you can try it in a small room and see what happens.

Answer 5

they will crack will out the proper sub floor

Answer 6

it has to be straight otherwise you wasted your time