Transitioning from concrete to floorboard, advice please

[happyhero]

Hi, I have tiled our extension/kitchen diner with 600mm x 900mm Porcelain tiles on top of a Warmup heated floor on top of 10mm Prowarm Backer-Pro tile backer board which is on top of a latex leveller on concrete but from the extension I now have to continue laying tiles on to the narrower original kitchen and it has old fashioned floor boards (NO tongue and groove).

The kitchen is about 2.6m wide and the kitchen is still in use so I can only tile into the suspended floor area up to about 500mm. The tiles I want to lay will be 400mm in the concrete side and 200mm in the suspended floor side.

The leveller has made it so that the concrete floor is virtually level with the suspended floor part so that laying the 10mm tile backer boards on to the suspended floor would create more or less the same height, so tile backer board level all through if wanted.

The house is 1930’s and I think the boards are original but ok.

I used Norcros S1 standard set (purple bag) which states how incredibly flexible it is and good for ply areas etc. It seems really good stuff capable of swimming pools it says somewhere etc, anyway I have few bags left. Apparently Norcros do an additive to make S1 into S2 if you really require it.

So whats best, what would make it the stiffest/sturdiest?

1.Should I remove the floor boards and make up the difference with plywood and if so what type?

2.Should I support the joists and if so with what?

3.Should I leave the floor boards and use the 10mm tile backer board (I have some left)?

4.Should I use ply on top (may be able to get away with 12mm since they don’t do 10mm) and if so which one, would this be sturdier than tile backer board?

Bear in mind at this stage I can only get into the suspended floor 500mm so across 2 joists at this stage but across full 2.6 width of kitchen.

Note: joists are running parallel to tiles I am about to lay.

Note: No heated floor going in the old kitchen but I will still lay the cable mat to create the same height (I have loads left)(it’s about 5mm thick I think).

Also when I take out the old kitchen, the suspended floor area what should I do there, bear in mind they are big tiles going on a suspended floor?

Any help/advice appreciated.

 

[Notch7]

I would remove the floor boards and fit plywood. Far Eastern external ply.

I would've used a ditra mat over whole area to decouple.

 

[JaimieH]

Any transition between concrete and wooden floors should have a movement joint incorporated into it and there should be no bridging of the joint during the subfloor build up. Your two floors will expand, contract and possibly move vertically independent of each other so if you bridge the joint with anything and tile over it then it's very likely the tiles will fail. There are plenty of movement/expansion joints about to choose from so I'm sure you'll get one to blend in. Also you must ensure there is no flex in the wooden floor before doing anything. As for building up to the level of your existing floor my choice would be construction boards like your pro warm backer boards laid over the floorboards. I wouldn't bother laying the heating mat if your not going to use it, the construction boards come in various thicknesses.