Cavity drain cellar tanking - how to finish?

[Nicobobinus]

Dear DIYnot,
Longtime lurker; first time poster, so be gentle!

We're currently having our cellar tanked with a cavity drain system (Wykamol). It's the full works: membrane on walls & floor, perforated channel around the outside, sump with twin pumps, and I think I understand how it all functions reasonably my well.

The firm doing the work have done a neat hm& thorough job, but have left the membrane 'open' at the top, for want of a better description: the dimpled plastic isn't sealed at ceiling height.

Should it be...?

To my mind, not sealing it would allow water vapour to rise out of the top and the cellar will still be humid.

Anyone know how best to finish it? Is it normal to be open? Anyone had similar work done: how is yours finished?

Thanks for your time!

 

[DAZB]

In my experience, and i have done several of my own properties, it is ok to be left open at the top. The provision of airbricks will help deal with moisture from the cavity and leaving it open also helps air to circulate from what will be a lived in heated room. The Wykamol website has PDF's for download that show the installation detail and you could always drop them an email to be sure.

 

[freddiemercurystwin]

Whenever I've detailed these types of systems, Newlath, Delta etc, I've never shown it stopping short at the top, check with the manufacturer. Just ask to speak to their technical department rather than faffing about with emails.

 

[Nicobobinus]

In my experience, and i have done several of my own properties, it is ok to be left open at the top. The provision of airbricks will help deal with moisture from the cavity and leaving it open also helps air to circulate from what will be a lived in heated room. The Wykamol website has PDF's for download that show the installation detail and you could always drop them an email to be sure.

Thanks for your insight. The firm doing the work indeed suggest that the climate control system will deal with any water vapour, but I'd rather cut it off at source.
They say they don't seal the top because the sealing tape doesn't adhere to brickwork, which I can well believe.
I've searched the many, many pdfs on their site but they seem to concentrate, understandably, on the floor and floor/wall junctions. Can't find a single one that details ceiling-height finishing!

Whenever I've detailed these types of systems, Newlath, Delta etc, I've never shown it stopping short at the top, check with the manufacturer. Just ask to speak to their technical department rather than faffing about with emails.

I was hoping you'd turn up, FMT! You seem to be a regular source of experienced knowledge on cellar tanking around here.
How do you finish off the top of cavity drain membrane? Do you stick it to the wall somehow?
I must admit I've emailed them at first, purely to be able to include pictures (thousand words, etc.)

I had a mad idea of sealing the gap between membrane & wall with spray foam. Is that silly...?

 

[freddiemercurystwin]

Ideally you would just finish the membrane level with the underside of the floor and then apply a tape over the junction, I daresay they'd have a standard detail. Or the membrane should be finished say 150mm higher than the ground level outside. If the ground level is higher outside and the wall is prone to getting damp you've got bigger problems anyway. I would just clean the brickwork with a wire brush just to get rid of the cobwebs/surface dirt and apply some tape to the junction. To get finickity the proper detail might include applying a suitable primer to the brickwork before applying their tape.

What's being applied to the walls next - insulation, then a vapour barrier and then plasterboard?

 

[Nicobobinus]

No, the cavity drain membrane is the final finish; it's not going to be a habitable space, just useable without things going rusty & mouldy. I've read there'll be an issue with condensation on the outside (inside...?) of the membrane, which is why I'm trying to get the humidity down as much as possible.
The paint-then-tape is a great idea! Did you come up with that or have you seen it specced somewhere? Thank again.

 

[freddiemercurystwin]

Well they'll have their own standard detail or recommendation for it I imagine, why not ring them and ask them? As mentioned in the plast I've just finished it flush with the underside of the soffit.