I'm a bit confused

[SandyFloor]

Whenever someone comes on the site looking for advice on preparing their chipboard floor it's usually either 15mm ply or 6mm backerboard screwed and bonded.

I'm assuming it's 15mm to give the floor extra rigidity but to the best of my knowledge there's little rigidity given by 6mm backerboard especially as it comes in smaller panels.

What am I missing here?

 

[user123]

I have no idea and think that's a really good question! Maybe backer board is just more stable in general?

 

[Andy Tiler]

cement backer board is the best substrate to tile on if the floor is rigid enough. if not 15mm ply will give xtra rigidity to the floor

 

[White Room]

The floors should be rigid before fixing.........

As MG the hardie is more stable to moisture, I don't use ply