Dry-line or Floor Levelling First?

[LeanTwo]

I'm at the stage with my single storey extension to start on the internal work.  First-fit electrics are in and I'm now looking at dry-lining after the insulation goes in between the rafters.  The floor slab went down some time ago with its dpm but it and the quarry tile floor of the old kitchen-diner will need levelling with some sort of screed. 

 

What's best to do first?  Should I level the floor and then work the plasterboard to that level or plasterboard and then pour the screed?  I've had advice favouring both! 

 

I have been told that I should ensure the plasterboard is slightly raised from any floor (as it loves to take up any moisture) so should be packed by a few millimetres on the bottom.  I'm proposing to put an underlay on the screed (possibly with another semi-permeable underneath it) and then laying an interlocking engineered timber, final floor.  I'm planning to dot and dab the plasterboard onto the inner leaf thermal blocks.

 

Any advice on how to go about this stage would be helpful, including making any provision for skirting boards!

 

 

[lizzie]

We have had to have our entire slab levelled prior to tiling. Our expert advice from floorlayers doing the job was that they wanted the walls plastered first and yes a gap between floor and bottom of plasterboard is the right thing. You cover this gap with your skirting board or in our case skirting tile, our final gap after levelling and tiles down looks to be somewhere around an inch but I have not measured it.

[Nickfromwales]

1 hour ago, LeanTwo said:

and the quarry tile floor of the old kitchen-diner

Is there a damp course under this floor? You may well have to apply a liquid DPM on top of this first as a mitigation measure. 

Dry line before levelling by all means, if it's your preffered route, but you mustn't leave the dab or boards in contact with the old floors or they'll likely wick moisture up and fail.

Id apply a couple of coats of liquid DPM between the floor and wall junctions before dry lining in case any dab drops down behind the board and bridges the floor and wall. 

Likewise with the self-leveller. You don't want that running under the plasterboard and bridging the damp that way either as that would cause even more issues. 

On the new work this issue is minimal to zero, but on the existing / old / unknown it's imperative you don't overlook these preventative measures.  

[LeanTwo]

Thanks for the replies, all very useful.

 

My slab does have a dpm (and the building control officer checked it all out).  However, I've been advised to think about another dpm before I put the underlay down for the wood floor.  Is this a breathable membrane or could I use the can of Black Jack bitumen emulsion that I've got?  Guessing that I could use this to seal the floor/wall junction as well?

 

I'll allow 25mm (1") from the slab to the plasterboard, which should allow sufficient clearance for any self-levelling compound that runs back to my blockwork, under the plasterboard line.

[Nickfromwales]

5 hours ago, LeanTwo said:

Thanks for the replies, all very useful.

 

My slab does have a dpm (and the building control officer checked it all out).  However, I've been advised to think about another dpm before I put the underlay down for the wood floor.  Is this a breathable membrane or could I use the can of Black Jack bitumen emulsion that I've got?  Guessing that I could use this to seal the floor/wall junction as well?

 

I'll allow 25mm (1") from the slab to the plasterboard, which should allow sufficient clearance for any self-levelling compound that runs back to my blockwork, under the plasterboard line.

Ok, but at the very least I'd fill that void with foam before levelling. Not just as a preventative measure to stop it bridging the wall / slab junction, but also to stop the levelled from escaping down the gap. Don't underestimate how bad that is for levelling, as literally bags worth can just pour down there whilst it's settling so 'pouring' money down there plus you won't have a level floor. .