Differing floor height and substrates in different areas

[chris_o]

See pic below.

Basically that small separate room was used as a cupboard, which is now being turned in to a shower with a low level tray. The floor in here is made up of old Victorian quarry tiles which are pretty soiled.

The bathroom itself has a suspended floor. The trouble is the shower area is approx 25mm higher than the suspended floor in the bathroom, and I need these 2 floors to be level as to tile straight through.

I've thought of a few options but need opinions. Do I raise the level of the bathroom floor with 18mm ply on top of the existing boards, then 6mm cement board fixed with adhesive to the ply? This will bring it up to pretty much the same level of the shower room. I also need some de coupling membrane to bridge the threshold between solid and timber floor, can this be used in a small section as opposed to over the whole floor?

Or do I remove the tiles etc in the shower area and re-screed, then just fix 6mm hardibacker to the existing floorboards in the other area? This will mean the floor in the bathroom area won't have to be brought up as far, reducing the height in to the room. Only thing is I want to be able to tile the shower area within 7-10 days?

 

[vinn]

In the pic: you have a suspended floor, and a solid floor - is the solid floor the high floor?
What are the tiles presently laid on.
Is that concrete or compacted earth or something else?

 

[chris_o]

Thanks for the reply.

The solid floor is the high floor. Today I have removed all the tiles, and dug about 100mm out below them. They were laid on about 20/30mm screed/concrete, with compacted soil and hardcore under.

My plan now is as follows:

The suspended timber floor is very solid, so after the plumbing has been completed I will screw all the floorboards down, and overlay with 6mm cement board, bed on tile adhesive and screwed also. In the solid floor area I will put down a dpm, then lay a 80mm or so screed using bal quickset cement whcih can be tiled on after 48 hours. I will make the finished screed height the same as the finished height of the cement board in the suspended floor area.

Does all of this sound correct? One thing I am unsure of is whether to use a de coupling membrane to span the threshold of suspended to solid floor?

 

[vinn]

Decoupling membranes, and similar, are best practice used over the whole area of both rooms with a break at the join.
At the join a control strip is best.
Your call - but you could risk using the control strip only without any membranes.

No need for expensive quick-set materials - simple sand and cement are sufficient for an 80mm screed.

 

[chris_o]

Will have a look in to a control strip then.

The only reason I have gone for quickset cement is that it can be tiled over after 48 hours, whereas a normal sand and cement screed I could have to wait 4-6 weeks t that depth?