Help!: Kitchen, Dining room Floor.

[alex blake]

my dilema is: two different types of floor (in the same room) half concrete half chipboard. Both of the same level. can it be tiled without causing a crack where the floors meet. Bearing in mind that the chipboard floor will have to be sheeted with ply.

[Daz]

Of course it can be tiled....How much do you want to spend on the prep work, what tiles are you looking at, can you live with an expansion joint where the 2 substrates meet?

[alex blake]

Of course it can be tiled....How much do you want to spend on the prep work, what tiles are you looking at, can you live with an expansion joint where the 2 substrates meet?

My plan for preping was 12mm ply onto existing chipboard floor, screwed every 150mm, then with a 12mm screed onto the existing concrete bringing it upto ply wood level. If you're recommending a expansion joint thats good enough for me. The tiles are going to be polished porcelain. Does that sound ok? Thanks Alex.

[Daz]

What condition is the chipboard in? Is there any deflection (bounce)?

Your suggestion seems fine, just remember to continue an expansion joint from where the 2 substrates meet directly up through the tiling.

Here's a couple of other suggestions for you to consider....
1. Why not replace the chipboard with 18 / 22mm wbp plywood? This will give you the opportunity to add extra noggins to the floor and maintain the same floor height as the existing screed.
2. If there is no deflection in the chipboard floor, you could glue and screw 6mm cement boards to the chipboards. This means that you will have a stable and tileable substrate and will only use half as much slc to bring the screed height level.

Whichever option you choose to go with, you will have to incorporate an expansion joint so that will be your main restriction, IMO.

Good luck,

Daz

[Stewart]

12 mm ply is too thin IMO. If the timber floor is deflection free you could glue and screw 6mm cement board.

[Perfect Tiling]

I could be totally wrong here but if the chipboard part of the floor is deflection free and overlayed with 6mm hardibacker, then the concrete side is brought up to level with slc, can a decoupling mat be used over the whole area which will bridge any crack that may appear underneath it. I have used the Genisis GMAT on floors with good sized cracks in them as this is its purpose.

[grumpygrouter]

I could be totally wrong here but if the chipboard part of the floor is deflection free and overlayed with 6mm hardibacker, then the concrete side is brought up to level with slc, can a decoupling mat be used over the whole area which will bridge any crack that may appear underneath it. I have used the Genisis GMAT on floors with good sized cracks in them as this is its purpose.

I thnk the definition of deflection free is relevant here. A timber floor will NEVER be as solid as a screed floor in my opinion, and a decoupling membrane would probably not be the answer. Not only that, as the timber is a "living" breathing product, it may well swell slightly as well as increase/decrease in length due to moisture/heat variations.
I think you will probably find that the membrane data sheets also specify that expansion joints should be carried through the membranes also.