slab to wall joint when screeding

[trumansparks]

Having had previous advise on here my slab is now down in the front room,

I now need to level and finish with a screed, but am unsure/ cannot find answers on how to approach the edges of the slab

construction of floor is
sub
sand
dpm
celotex
dpm
concrete

celotex was put all around the sides to insulate and as a shutter,

1, do i trim down celotex to concrete level, fold dpm's over and screed over the top to meet the wall?
2, also as soil sub base behind the side insulation their is an irregular gap to base of wall soil, do i fill this with the screed too?
3, Where do i trim off the dpm too? above screed into wall or under screed at concrete top?
4, I have extensively googled and not found any diagrams or information, any links people have found would be welcome!
5, as i am laminating, is it worth leaving the screed slightly lower than the other floors so that the levels will match when laminate is layed?
notes, walls are old stone, lime plaster, no dpc,

many thanks,

truman

 

[noseall]

I am a "fit the insulation under the slab" kinda guy.

 

[RedHerring2]

Having had previous advise on here my slab is now down in the front room,

I now need to level and finish with a screed, but am unsure/ cannot find answers on how to approach the edges of the slab

construction of floor is
sub
sand
dpm
celotex
dpm
concrete

celotex was put all around the sides to insulate and as a shutter,

1, do i trim down celotex to concrete level, fold dpm's over and screed over the top to meet the wall? I wouldn't in your case. You'll create a thermal and damp bridge. This wouldn't occur in a new cavity, insulated wall. The 25mm(?) of insulation will be covered by skirting.
2, also as soil sub base behind the side insulation their is an irregular gap to base of wall soil, do i fill this with the screed too? No, as above.
3, Where do i trim off the dpm too? above screed into wall or under screed at concrete top? I would trim at least 25mm, pref' 50mm above screed, behind pb and skirting.
4, I have extensively googled and not found any diagrams or information, any links people have found would be welcome! You have an unusual setup, not that unusual for renovations, but it wouldn't be done like that as new.
5, as i am laminating, is it worth leaving the screed slightly lower than the other floors so that the levels will match when laminate is layed? You could also use threshold strips to even out any change in levels.
notes, walls are old stone, lime plaster, no dpc,

many thanks,

truman

 

[trumansparks]

Cheers guys,

noseall, are you suggesting removing the side insulation? i have read its use is less important on interior walls. so could leave just the one at front wall. how to fill the gap?

redherring thanks for the answers, although still alittle unsure what to do about the top of the side insulation, from edge of concrete to walls is approx 3 inchs so too big to leave in my opinion.

cheers
truman

 

[seasickstevie]

... is it worth leaving the screed slightly lower than the other floors so that the levels will match when laminate is layed?

Definitely.
I forgot to do this with mine (even though someone suggested it to me at the time) and I ended up having to raise the floor in adjacent room to meet to new hardwood overlay.

 

[RedHerring2]

although still alittle unsure what to do about the top of the side insulation, from edge of concrete to walls is approx 3 inchs so too big to leave in my opinion.

Aaah, you didn't mention that before. Normally the upstand is only 25mm to prevent the cold bridge.
Even so, I would still not screed over it. Leave the upstand to level with the top of the screed, then lay the finished floor over the top of the upstand, depending on your choice of finished floor. I'm asuming that you still have to fix pb and skirting which will cover about 40mm of it, more if you're using insulated pb.

The other alternative is to trim it down to the 25mm upstand where it is between the screed and wall, that is more usual and will prevent the cold and damp bridge. Obviously your dpm is preventing the damp bridge and should continue at least 25mm preferably 50 mm behind pb/skirting.

 

[trumansparks]

although still alittle unsure what to do about the top of the side insulation, from edge of concrete to walls is approx 3 inchs so too big to leave in my opinion.

Aaah, you didn't mention that before. Normally the upstand is only 25mm to prevent the cold bridge.
Even so, I would still not screed over it. Leave the upstand to level with the top of the screed, then lay the finished floor over the top of the upstand, depending on your choice of finished floor. I'm asuming that you still have to fix pb and skirting which will cover about 40mm of it, more if you're using insulated pb.

The other alternative is to trim it down to the 25mm upstand where it is between the screed and wall, that is more usual and will prevent the cold and damp bridge. Obviously your dpm is preventing the damp bridge and should continue at least 25mm preferably 50 mm behind pb/skirting.

thanks,
The upstand is 50mm and i can find a particulatly deep skirting board for the room although the walls are being plastered in lime not boarded it should give another 10 mm ish too. i guess then its unlikely for someone reverse into the skirting and put a stiletto through the floor.

does the gap between the upstand and wall just get left then? heard something about a resin but can't remember details.

thanks again
truman

 

[RedHerring2]

.The upstand is 50mm..... .
....does the gap between the upstand and wall just get left then? heard something about a resin but can't remember details.
.

That's 2".
You can fill the gap with lime mortar for the best effect, but cement mortar or concrete would be OK.
I'm assuming it's just the uneveness of the stone wall.

 

[trumansparks]

.The upstand is 50mm..... .
....does the gap between the upstand and wall just get left then? heard something about a resin but can't remember details.
.

That's 2".
You can fill the gap with lime mortar for the best effect, but cement mortar or concrete would be OK.
I'm assuming it's just the uneveness of the stone wall.

great help redherring2,
yes its the irregularity of the stones at the base of the wall, had to try for as straight an edge as i could for celotex shuttering which left the odd gap/void etc and didnt allow me to get very close to wall in many places.

So to recap i will use a lime mortar to fill gaps to wall all round back of insulation then trim it down to top of screed level. Then screed the floor and tuck dpm over top of now flat insulation and up under skirting.

crikey, i hope i have understood this correctly. many thanks for the patience and help.

truman

 

[RedHerring2]

You could use concrete or cement mortar 'cos there will be no breathability there, the dpm will prevent that.

Next time use a 25mm thick insulation for your upstand, it'll take the contours of the wall better. Any gaps in the floor insulation can be filled with off-cuts.

If you're planning on using a wooden skirting, give it plenty of preservative before you fix it.

When I did my floor I packed out deep hollows and padded any sharp bits with bits of 25mm insulation.
//www.diynot.com/forums/viewtopic.php?t=237971

 

[trumansparks]

nice job red herring2 makes mine look rather easier than yours must have been,

will look at your other posts on it, looks a nice project to me.

will post back when completed,

out of interest whats the easiest way to find the right levels, was thinking of using a lazer level and blocks on floor as cant mark the walls due to the dpm.

truman

 

[RedHerring2]

If you look at the pics of my place you'll maybe just see a datum line in red around the wall, about 1m up. Placed with a laser level. I sprayed a line marker up against a piece of wood to give a clean bottom edge to the line. Checked afterwards with a spirit level.

Measure down from this to fix a wooden batten 25x50mm around the wall, it'll also hold the dpm up out of the way.
You can either bring the concrete to the top of the batten, as I did, or to the bottom. In which case you'll have to notch out your tamping beam, or work freehand.
Or, maybe, as in your case, fix the batten above or where the screed will finish and notch out a tamping beam to accomodate the height.
The screed will take out any variation in the concrete. A variation of 20 or 30mm in the concrete level will be no problem as long as you have 30mm minimal screed thickness. You could possibly reduce this very slightly by using a SBR/cement slurry on the surface of the concrete to help the screed to bond.

I found 100 or 150mm nails the easiest way to fix the batten, straight into the mud like mortar. Occasionally a good fixing into the stone.

Your screed can be done 'freehand'. Divide the floor into bays, setting out battens laid on the floor and levelled. Screed laid to them, then when that 'bay' is complete lift the batten and infill.