Replacing (ground floor) floorboard section with concrete

[masmith79]

I am about to undertake a bathroom project and the boss (my missus) has insisted she wants ceramic floor tiles layed.

At the moment the bathroom (approx 3m x 3m is mostly concrete, all except for a square of floorboards (approx 0.75m x 0.75m) near the doorway as too is the flooring in the hallway. These floorboards have over the years become rotten and are now at death's door.

(not to scale) (green being DPM)

I have decided to remove these floorboards from within the bathroom and fill in the void leaving a concrete finish. Am I correct in suggesting this method:

1. remove floorboards and joists.
2. Fill in joist holes in wall with brick/mortar
3. Create concrete resevoir to height of dpm to contain hardcore
4. "Chip" back existing concrete floor to reveal more existing DPM (I heard this should be about 8" to allow a sufficient join)
5. Compact hardcore into "hole" and finish with a layer of compacted sand to level of existing dpm.
6. Join new dpm to existing dpm covering entire sanded area.
7. Create shuttering to contain concrete
8. Fill in with concrete
9. Screed a level suface to finish

Is this method ok?

My other option was to replace the joists and lay a panel of 12mm marine ply instead of floorboards. However this may cause problems with the tiles due to expansion/ contraction of the wood.[/img]

 

[alfiembra]

Don't quite follow step 3, what do you mean by concrete resevoir?

From your description if you have an existing dpm then your old slab is already built on the solid and is not suspended. So whats under the wooden section? is it a void, in which case what is holding back the fill material/hardcore to the existing slab. What sort of depth are you filling to the underside of the old slab.

step 7: does your old slab not already form the shutter to your infill section?

Alan