Membrane finishing

[Spinny]

Hoping to have the flooring peeps in soon. Wondering how I should prepare the various membranes poking out at the windows and bifolds. (See pics)

1. The window people put a piece of DPM under the bifolds and floor length window. They used double sided tape to stick it upwards against the inside edge of the frame/threshold on the inside. Naturally the DPM has pulled away from the tape and the tape has become gummed up with dust and crap and is no longer sticky. Should I scrape and cut the tape off the frame/threshold, and then what should be used to restick it ?

2. The floors radon/dpm membrane is directly alongside the window DPM. Thinking of sticking this to the window DPM, and then the floor levelling compound should run up against it when they pour it.

3. The black vapour barrier is then on the inside of the 25mm PIR edge insulation. Either I cut this off at the current floor level and it gets covered along with the edge insulation by the floor leveller. Or I try and cut it down to fold over the top of the edge insulation and then get covered, possibly sticking it too to the radon/dpm.

4. The window DPM has got  a short 20mm cut in it just outside the window - how do I repair this ?

 

Many thanks.

[Spinny]

Any thoughts on this one folks ?

[jack]

@craig, is this something you could help with? Many thanks.

[craig]

On 06/04/2026 at 21:22, Spinny said:

1. The window people put a piece of DPM under the bifolds and floor length window. They used double sided tape to stick it upwards against the inside edge of the frame/threshold on the inside. Naturally the DPM has pulled away from the tape and the tape has become gummed up with dust and crap and is no longer sticky. Should I scrape and cut the tape off the frame/threshold, and then what should be used to restick it ?

 

Sticky tape? They should have used something like CT1 or stickslike***t would have been good enough and then trim if required.

 

On 06/04/2026 at 21:22, Spinny said:

2. The floors radon/dpm membrane is directly alongside the window DPM. Thinking of sticking this to the window DPM, and then the floor levelling compound should run up against it when they pour it.

 

Should be fine, not much else you can do from what I can see.

 

On 06/04/2026 at 21:22, Spinny said:

4. The window DPM has got  a short 20mm cut in it just outside the window - how do I repair this ?

Any left over to patch? If yes, stick over the top with the adhesive mentioned previously.

Edited April 9 by craig

[Spinny]

Thankyou.

Any input on Q3 ?

 

I am relieved to see stickslike***t doesn't come in brown.

[craig]

13 minutes ago, Spinny said:

Any input on Q3 ?

 

Fold it over the top of the PIR and seal it to the DPM/radon barrier I think would be the best approach.

[Spinny]

OK.

Around half of the room/extension perimeter one of the builders cut off the vapour barrier to slab level as soon as the concrete slab had set. I caught him before he could do the other half. The Architects drawing was for it to run to the wall behind the skirting and get plastered onto the wall, although the plasterers thought that daft. The 25mm edge PIR is inevitably tightly pushed against the inner leaf blockwork by the weight of the concrete pour, so I guess not much chance of any colder air from below the concrete making it through to the room anyway. Certainly over 2 years of of it being in place we have had no sign of any such issue or condensation or anything.

 

Fortunately the radon barrier was run into the cavity wall and up to join the wall DPM so no-one could cut that off.

 

Just googled whether PIR is vapour permeable and got this AI response...

 

Quote

PIR insulation, even without foil, is not considered vapor permeable; it is generally classified as a vapor retarder or a low-permeance material. While removing the foil (e.g., using tissue-faced PIR) increases its permeability slightly compared to foil-faced versions, the closed-cell foam structure still significantly resists moisture movement, preventing it from being "breathable".

 

So I guess slightly better to do as you say, but if the flooring people want to cut it off it shouldn't be a problem ?

 

[Spinny]

oh sorry Craig or others, just thought of another question(s)...

 

I have a set of twinwall flexible conduits and a 110 drain pipe coming up under the kitchen island position carrying insulated water pipes and cables etc. Therefore these come up through the concrete. Is there something I should do to try and seal up the top of the surrounding hole around the conduits. I can't say how well membranes were cut and sealed to the conduits - knowing our builder probably not perfectly.

 

Q5 I guess definitely not a good idea to use floor leveller there for fear it all runs down the hole into the insulation layer ?! Maybe try and practice my insulation carving again and try and cut some 30mm XPS slab to fit around the pipes ? What do people usually do

for this ?

 

Q6 Re conduits themselves with pipes/wire coming out under kitchen units etc - any need to seal the ends around the pipes/wires to stop air moving along the pipe from colder levels ?

See pics

 

[craig]

It’s not really my area of expertise tbh but @Nickfromwales might be able answer these questions better than I can?

[Russell griffiths]

Trim off all the foam layer down to screed level

get a can of illbruck fm330 foam, good squirt around all ducts and down the ducts, as it dries and expands a bit you can pat it into shape or just trim it back afterwards. 
or don’t bother trimming and just leave a big blob under the cupboard if your worried about catching the pipes or cables. 

[saveasteading]

11 hours ago, Spinny said:

another question(s)...

Having just had this done I can advise one concern.

The guys putting the insulation in were very cavalier at such intrusions, and were keen to hurry the job and get away. Anticipating such issues I put my heel on the membrane at all such, and one gave way drastically. I settled on the fact that screed would fill the dent and make it solid. That's provided that the membrane isn't punctured and tape still in place.

 

In your case thus concern applies outside the green foam. Inside the green circle perhaps stuff with insulation offcuts and put a sandcand cement screed on top.

 

For anyone approaching the insulation stage I'd say either watch these guys all the time or do any fiddly cutting yourself and leave them with the easy cuts. Eg we had drain pipes with mortar bedding, some near stud walls,  leaving slopes into small voids. I spent a day cutting triangular pieces to leave a flat and solid surface, and very glad I did.

 

My mental test was to imagine a heavy concentrated load, eg bed leg or grand piano.

Under an island it is more a matter of tidiness 

 

 

 

[Spinny]

Oh dear, bought some stickslike***t.

It seems like when it comes to DPC membrane and radon membrane and powder coated aluminium that stickslike***t doesn't actually stick like ***t, it sticks like ***t.

 

I did a test run and when sticking these materials it just pulls/peels apart again.

 

Now I think the levelling today will have to be put off. Not sure what to try now ? Back to double sided butyl tape ?

I'd have thought this was a common issue/question for anyone with alu bifolds/cills etc ?

 

@Nickfromwales or anyone ?

[craig]

CT1.

[Spinny]

OK, thanks craig. Looks like it is going ahead today anyway with just taping the membranes up against the windows, then cut off to levelled floor after.

I might stick some CT1 or something along the edge afterwards.

[Nickfromwales]

9 hours ago, Spinny said:

@Nickfromwales or anyone ?

Apologies, on a job that’s keeping me busy atm. 
 

7 hours ago, Spinny said:

Looks like it is going ahead today anyway with just taping the membranes up against the windows, then cut off to levelled floor after.

I would have said this.

 

Glad they carried on, and you’re making progress.

[Spinny]

@NickfromwalesThanks. It is just so impossibly difficult to get each step actually complete though.

They didn't have enough of the levelling compound to quite complete the job for the first pass levelling ! 

And something about coming back to sort out the edges.

 

They did use little 'soldier sticks' stuck to the primer to create a levelling guide and the mix was free flowing so found it's own level. Although they did use a spirit level to level the soldiers 2 at a time and I know from experience that you can use a spirit level 4 or 5 times end over and end up 4/5mm out of level over 8m quite easily. However the mix was free flowing anyway so probably irrelevant.

 

It is difficult to understand how pro's can run out of material. When you are doing a trade week in/week out you would think what doesn't get used on one job gets used on another and you always have some spare floating stock at your premises. Most stuff doesn't time expire for months. Materials are generally much cheaper than labour. The cost of coming back to finish an incomplete job will greatly exceed any loss from over ordering. Cost of 10 extra bags about £200 retail, cost of another delivery, another trip, the double handling, 2 people for another half a day, rescheduling jobs, inconveniencing another customer etc probably £400+.  Make it make sense because I can't.

 

It is progress but, still frustrating. Plan the job well, do it well, complete it, move on. ugh

Edited Friday at 18:45 by Spinny

[Spinny]

Is this acceptable ? Should I be complaining ?

 

So from friday we left the floor leveller to dry and so have just taken a quick look. Not impressed really.

Not only did they run out of levelling compound and leave a section unfinished, but sections do not appear to be very level (see photos).

There is a dip of up to 5mm across a 1.8m level at one point.

The surface falls by 10mm into the doorway across a 1.8m level.

Where each mix was poured and spread there are some small but noticeable ridge lines at the junction curves.

 

I didn't expect perfection, but I expected something better than this ?

 

Yes the plan has been to put a second coat of 3-4mm across the top and continiously over the suspended floor down hall and utility. But not what I was expecting as the starting point for that.

 

What do people think ?

 

I feel like making them do it again - what would be the implications of two coats where there should be one - would it need roughening to provide a key ?

 

[Oz07]

Did they roll with spiked roller? Looks a bit gash. Remind me whats going ontop?

[Spinny]

AI says this...

 

https://www.google.com/search?q=standards+for+floor+levelling&oq=standards+for+floor+levelling&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIICAEQABgWGB4yDQgCEAAYhgMYgAQYigUyCggDEAAYogQYiQUyBwgEEAAY7wUyBwgFEAAY7wUyCggGEAAYgAQYogTSAQoxMTU1NmowajE1qAIIsAIB8QWtHVJdU_RSivEFrR1SXVP0Uoo&sourceid=chrome&ie=UTF-8

 

No laser level was used.

They ignored the markings I had put all around the walls using my water level.

They stuck down a few self adhesive soldiers with the tops levelled by using a 1.8m spirit level (same level make as mine, not a 'professional' standard level)

No spiked roller or squeegy was used at any point. Just a bit of hand trowelling to spread it.

One young lad mixing, older guy pouring/spreading.

Ran out of compound - it was obvious to me this would happen when they reached halfway and had used 2/3rds.

One came back the following day to fill in the edges by hand with a different compound (I'd have thought the first compound should run wall to wall.)

 

The final floor will be adhered LVT plank with no threshold between concrete and suspended floor - i.e. running from the front door through to the rear bifolds, in a continuous 'look through the house' layout.

 

Yes their plan has always been to level out the concrete (max deviation about 30mm), then put smoothing compound of 3/4mm over everything, then stick the LVT to that. So never necessary to achieve a perfect levelling result without surface imperfections, but levelling is levelling.

 

Edited 10 hours ago by Spinny

[saveasteading]

3mm under a 3m straightedge  is the official measurement for industrial floors but I haven't checked re domestic.... logically it should mob be less stringent.

That is in any direction and includes if you press down one end and measure under the opposite end. But finding a 3m straightedge isn't easy.

 

Tiling adhesive will take out minor variations, but for LVT I think it could be a big issue 

Probably needs local filling.

[Spinny]

Their T&C's says they may not be able to achieve SP1 = 3mm over 2m. But they have been telling me about laying floors in Paris for sheiks, and their next job is a luxury hotel.

 

My suspended timber joist hallway is more level than a professionally levelled concrete floor ?

 

If a floor is 5mm out over 2m then your dining table is going to rock - on a brand new floor. 

[Spinny]

@Nickfromwales any comments ?

 

A good plastered wall might vary by 3mm, and a plasterer doesn't have the benefit of gravity.

[Russell griffiths]

Have you been and seen their finished LVT workmanship 

if not then stop now. 

[Spinny]

6 minutes ago, Russell griffiths said:

Have you been and seen their finished LVT workmanship 

TBH no. They are locally based and have been used by people that have declared to us that they have been happy with their work. They have good reviews, and do work in high worth properties in the area. Their flooring expert has been a few times as we have been so delayed and always seemed knowledgeable. One concern is that the guy doing the work is probably over 60 now like me.

 

I am now minded to ask for details of another customer they did LVT for - to go and take a look.

I feel I have got a friday afternoon job. It didn't start well when they were supposed to start on Thursday but ended up just bringing the materials after they were delivered mid morning. Friday was the first time the guy doing the work saw the job.

[Nickfromwales]

3 hours ago, Spinny said:

@Nickfromwales any comments ?

Yes. The levelling is shit, and their management of your expectations equally shit.

 

If I am going to fail to get a floor perfect, for whatever reason(s), I tell the client before hand so they know what to expect; that allows opportunity to explore options, and for a compromise to be agreed.

 

You can't just have depressions that bad on a new floor, and rectifying it is relatively easy; just add spot-filling with compound over primer and then block the floor to remove the steps where the 'waves' of leveller are apparent.

 

Using a dimpled roller is great for general levelling, but if you're rectifying areas then you don't roller it as you don't want the leveller to migrate from the area you want to improve.

 

Talk to them in the morning and completely lay your cards on the table, and ask these questions and get the answers directly, as all you're doing here is venting and not resolving, as we're not laying your floor.