Floor deflection

[jimmycooker]

Hi Lads,

I have a wetroom I need to tank, it is 4m x 1m (with marmox showerstone tray taking up 1m2 at one end).

I floored the rest of the upstairs & wetroom with 18mm WBP.

I have just realised / noticed that there is a join in the ply running perpendicular to the joists right at the door entrance where traffic will be heaviest.

I realise now I should have battened in between the joists, is there any way around this?

I have 30mm between the top of the ply and the bottom of the glass door.

How much space will a standard tile, grout, tanking take out of the 30mm?

Would a 10mm marmox board or something on top of the WBP stop the deflection without additional battening between the joists?

Thanks,
James.

[Rich]

The boards will not add any strength to the floor, the WBP ply needs to be deflection free before you over board Im afraid. Is there nothing to screw down into? If not then I would have to say that it is worth lifting the ply and sorting it out. No simple way round it as I can see and the floor MUST be deflection free before you tile.

[jimmycooker]

The only thing is that the joists are 70mm wide and at 350mm centres (280mm gap in between).

If I boarded over the join with 10mm wbp or cement boards don't you think this would do the trick?

[Rich]

To be honest, no I dont think it would do it. No matter what you overboard with you will still have the deflection underneath. Is there no way of lifting the boards and adding some noggins?

At the end of the day, it will be down to you. If you want to give it a go over boarding to see if you can loose the movement, that is up to you, but I dont think it will solve it. Cement boards give you a suitable surface to tile onto, they dont offer any strength to a floor and if the floor under them is moving then they will move and ruin the floor.