Floor Screed over a Cavity ? (New French Doors replacing Cavity Wall)

[markyboy944]

Background: Old Cavity wall (which had a single door in it), has been removed, ready for fitting new wide french doors. The brick course where the door cill+frame will go has had to be "shaved" by 15mm, to allow the frame to fit (after helpful advice on here).

[Note - on the photo, the bricks look messy, but thats just because the diamond cutter could only go so far. I bolstered the rest, roughly, and will use angle grinder with stone attachment to smooth them off).

The "issue" is that I need to extend the footprint of the floor screed so it comes out to meet the door frame. I am aware that it's important to keep the cavity there, so I can't just go pouring concrete into the cavity (I don't think). My question is, how can the screed be "supported". Basically it will need to extend over the cavity (which is fresh air), so ... whats the best method to do this, and give it the strength it needs ?

NOTE - the shaved bricks are 15mm lower than the inner blocks.

I had (originally) toyed with the idea of a cavity closer, but I don't think that would be strong enough, as it's just plastic. (Also - now the bricks are shaved, it would tilt downward slightly at the door .

Many thanks in anticipation

 

[noseall]

Remove the masonry (both leaves) to 225mm below floor level. Line the trough with polythene. Fit insulation and fill with concrete to underside of screed level. Screed over the lot.

You may still get differential cracking, but there's not a lot you can do to mitigate that unless you go unfeasibly deep.

 

[markyboy944]

Remove the masonry (both leaves) to 225mm below floor level. Line the trough with polythene. Fit insulation and fill with concrete to underside of screed level. Screed over the lot.

You may still get differential cracking, but there's not a lot you can do to mitigate that unless you go unfeasibly deep.

Thanks for the reply. So, just so I'm clear, you are saying take out the blocks and bricks down to 225 below floor ? - Wish I'd never opted for French doors now - quite a lot of work !.

 

[noseall]

Thanks for the reply. So, just so I'm clear, you are saying take out the blocks and bricks down to 225 below floor ? - Wish I'd never opted for French doors now - quite a lot of work !.

Sorry mate - I thought you were building an extension!

 

[Notch7]

Thanks for the reply. So, just so I'm clear, you are saying take out the blocks and bricks down to 225 below floor ? - Wish I'd never opted for French doors now - quite a lot of work !.

With existing screed, your only option is to line cavity with DPM, and fill with concrete.

there will be differential movement at the day joint with the screed. If you are tiling you need to use ditra mat to isolate substrate from tile.

 

[noseall]

Thanks for the reply. So, just so I'm clear, you are saying take out the blocks and bricks down to 225 below floor ? - Wish I'd never opted for French doors now - quite a lot of work !.

Just take the blocks out and do as I said before. Leave the bricks.

 

[markyboy944]

No it already exists (snince 1983) , so I'm just wondering how to screed over the existing cavity (which is currently fresh air).

 

[noseall]

No it already exists (snince 1983) , so I'm just wondering how to screed over the existing cavity (which is currently fresh air).

Do as I said and ignore the outer leaf. You can't avoid removing the blocks. They are now defunct and a nuisance and will cause differential cracking if they remain. Make sure the polythene laps up the outer masonry.

 

[markyboy944]

Do as I said and ignore the outer leaf. You can't avoid removing the blocks. They are now defunct and a nuisance and will cause differential cracking if they remain. Make sure the polythene laps up the outer masonry.

Thanks mate. Wish I'd know this before I started. Seen videos online where people were using a cavity closer.

 

[noseall]

Thanks mate. Wish I'd know this before I started

It's no biggie. If you can put your hands on a small breaker or roto-stop Bosch, you'll be home and dry in a day. Do all the grunt work before the new doors go in.