Plastic sheet under threshold between rooms

richieboy · 30 Oct 2021 at 19:10

Evening,

I've got some LVT flooring in my hall and tile in my kitchen, between these two was a huge piece of wood for a threshold that my kids constantly trip over so I have removed it and plan on screeding/using some flexible type of concrete etc then using some of the spare LVT to put over the top and hopefully with a bit of work create a much smoother transition between floors (height is about the same, tile maybe 2mm higher)...but I've hit a snag...

There is this plastic sheet stuck in the concrete floor under where the existing wooden massive plank threshold was ..would you cut it out and screed/concrete over, or leave it in place and screed/concrete over it? Worried that if I leave it that whatever I put on top won't adhere properly to the plastic?

Cheers for any help.

thenewoc · 30 Oct 2021 at 19:21

I think what I'd do there is use a suitable underlay, something foam based that will flex a bit to absorb the irregularity of the surface. Some of these also have a dpm layer. Perhaps use a white threshold bar under where the door closes and cut a plank of laminate to go under the edge of that new threshold bar. You'll need to chisel the concrete edge away next to the tiles to make way for the threshold bar fixing strip. You might be able to get a suitable blade for one of them oscillating tools too. Something like a grout cutting blade would probably do it.

If underlay isn't thick enough you could cut a piece of hardboard to match the laminate plank size required and pop that underneath.

richieboy · 30 Oct 2021 at 19:39

Thanks, I would prefer to leave the plastic alone as presumably it is dpc related!

Any idea what sort of foam based product you're thinking of? Hopefully you don't mean like a foam underlay type that you'd use for carpet etc as the vinyl tile or whatever goes on top would just squish when walked on wouldn't it?! I think that's why I was thinking some sort of flexible compound that would set hard but still have a little bit of give in it (I've got some mapei keraquick flexible floor adhesive left in the garage I could use for example!).

thenewoc · 30 Oct 2021 at 19:42

Something like this but there are others too, various thicknesses...

https://www.screwfix.com/p/diall-aquastop-underlay-5m/2471r

Gav_r26 · 1 Nov 2021 at 08:37

Looks like vapor barrier put in to stop the build up of Radon gas in the house. Where in the country are you?

Radon Map

ANDARIAL · 1 Nov 2021 at 09:10

Gav_r26 said:
Looks like vapor barrier put in to stop the build up of Radon gas in the house. Where in the country are you?

Radon Map

Radon gas membranes are `usually`green or red and have `labelling` on them

What you `could do`is cut the membrane down the center,dig out for a depth of concrete say 4 inches put more dpm in the hole and fill with concrete with a waterproof additive
seen this done before but underlay/fill with packing is also a good/easy option

200sols · 1 Nov 2021 at 09:13

It just looks like standard damp proof membrane to me.

I'd just build it up on top of the plastic with some tile adhesive before laying the LVT.

Gav_r26 · 1 Nov 2021 at 09:56

ANDARIAL said:
Radon gas membranes are `usually`green or red and have `labelling` on them
What you `could do`is cut the membrane down the center,dig out for a depth of concrete say 4 inches put more dpm in the hole and fill with concrete with a waterproof additive
seen this done before but underlay/fill with packing is also a good/easy option

Ah yes ours was an olive green colour now you mention it! Been a while since our extension was done so cant remember all the technicalities now!

thenewoc · 1 Nov 2021 at 10:34

I'd put some silicone in the tares to the plastic and then put some wavy lines of silicone down to bed in a piece of stiff underlay board and possibly a piece of hardboard on top of that depending on the level that needs closing up to meet the same as the underside of the laminate.

Abyss · 1 Nov 2021 at 12:58

I'd just latex it up to the level required. Something like this:
https://www.wickes.co.uk/Setcrete-Latex-Floor-Levelling-Compound---20kg/p/133779

The DPM that's down should be kept.

thenewoc · 1 Nov 2021 at 13:40

Abyss said:
I'd just latex it up to the level required. Something like this:
https://www.wickes.co.uk/Setcrete-Latex-Floor-Levelling-Compound---20kg/p/133779

The DPM that's down should be kept.

Depends if the latex would be heavy enough to hold down the dpm as it's rippled with air underneath it. If the latex moves it will crack.

richieboy · 1 Nov 2021 at 18:10

Thanks all, I checked the radon map and we aren't near anywhere here, someone above has said that's usually green also so hopefully very unlikely and it is a dpm.

It seems deep enough that my tile adhesive will weigh it down and be deep enough that it shouldn't crack etc, I'll give that a go as if that works it'll give a nice solid surface under the foot, and if it doesn't work I'll have fun chipping it all out and trying a piece of board! Will definitely leave the dpm sheet in place now though either way, so thanks everyone.

LOAM · 1 Nov 2021 at 20:54

Radon barrier would not be laid over the slab, it would be worthless. Is it a door into an extension?

jellybeard999 · 1 Nov 2021 at 21:21

Is it deep enough to plywood then screed?

When I had LVT fitted they used Mapei 1-10mm and 10-40mm screed as appropriate, depending on the depths required.