Air Tightness, Internal Plasterboard, and Wall Sockets

[Mr Blobby]

2 hours ago, Gaf said:

Did you tape the membrane to the blockwork within the cavity?

 

No we didn't apply any tape in the cavity.  The tape above is temporary during constuction to keep the mrmbrane off the floor to protect it.  I read on another forum taht it was impossible to keep mortar off the membrane so I went totally OCD on this.

 

No need to tape in the cavity because the weight of the blocks above holds it in place ok, but in the days between the slabs going down and the FF blocks being laid, that is when it rained ono our site and the water pulled the membrane into the cavity.  Another reason to seal the ends of the slabs, for us it was worst where the end was not filled.  We needed to pull the membrane back up into place, but the blocklayers won't pause for anything so you need to be on site to make sure the membrane is still in the right place before blocks are laid on it!

 

The solitex membrane is incredibly durable but it is vulnerable to damage if blocklayers drop blocks down the cavity.  Happens rarely fortunately but woth checking and reapiring any damage with tape as you go.  In your second picure you have dpc over the membrane in the cavity, this is probably wise to protect it in the the cavity.  The membrane will eventually be taped to the walls as per your second image with contego solido tape and then plastered over.

 

Another thing I did was after the slabs were laid I went around and chipped off the sharp ends sticking into the cavity with a bolster to remove any risk of puncturing the membrane if it was pulled tight against the slab.  This is probably unecessary but was easy to do on a sunny afternoon.

 

The membrane will need to be managed at internal wall junctions (ours were not tied in so a bit easier) and internal corners are a nightmare.  

 

First course, some dpc over the membrane:

 

 

Later courses, the membrane was temporarily attached to the wall and covered with dpc to protect it:

 

 

 

... the membrane takes a lot of work.  It was ok for me because I had time to be on site a lot and I like a challenge.  It's far less hassle to fill the ends and have mortar and airtight paint above and (especially) below to seal the gap. 

Looking at ours now I'd say that the mortar above and below gives an airtight seal to the membrane and we don't need to do much more.

 

 

Edited February 2 by Mr Blobby

[Gaf]

@Mr Blobby Ah that's class. Photos are really helpful again to see what it all looks like. I'll be able to keep an eye periodically but probably not to the extent that you were. The builder seemed to know what he was doing / talking about, and mentioned being on site for some other things to 'supervise' the work. Seeing how you did it though I'll be asking how the membrane in protected for the FF block laying. Great to get the steer to the sharp parts of the slabs.

 

Sound!

[Mr Blobby]

14 minutes ago, Gaf said:

@Mr Blobby Ah that's class. Photos are really helpful again to see what it all looks like. I'll be able to keep an eye periodically but probably not to the extent that you were. The builder seemed to know what he was doing / talking about, and mentioned being on site for some other things to 'supervise' the work. Seeing how you did it though I'll be asking how the membrane in protected for the FF block laying. Great to get the steer to the sharp parts of the slabs.

 

Sound!

 

One thing to ask your builder about is the internal walls.  Mine aren't tied-in (as you can see in the pic above) but yours almost certainly will be.  It will be easier if you leave the bottom block not tied in (to keep the membrane flat against the inner leaf) and then tie-in from there up, but don't know if this is how its done down South. I'd be interested to know.

Edited February 5 by Mr Blobby

[Gaf]

@Mr Blobby Just to make sure I've understood (sorry I'm still getting my head around the terminology). I thought internal walls are a single row of blocks, so there's no ties for these, and ties are only used between the inner leaf and outer leaf of the external walls.

 

With the membrane, is it that I should make sure the membrane full 'vertical' from ground to first floor, or the membrane should be 'tucked' under the first floor internal blocks?

 

[Mr Blobby]

My crap terminology is at best misleading here 🙄

 

I'm certainly no expert nor am I a bricklayer, but I can tell you what we did and why.  Using the diagarms below, internal walls are, AFAIK, usually built "toothed" into the inner leaf of the external wall. 

The issue with this using the diagram below is that at the FF the membrane from below would not sit vertically against the first course of the external wall.   The membrane would be flat on the floor, as in your image on the right, which is wrong.  The membrane must be plastered into the external wall. 

Block layers would normally lay the first block at a right angle to build the corner as below.  Where there is a membrane the first block of the internal wall would need to be the second course, with the membrane against the first course.  My guess is brickies wouldnt like this!

 

We actually used the second method, with wall ties between the external and internal wall.  (you can see the ties in my image above if you look close)  Not sure if ties are the best approach, though,  certainly not the most structurally stable and at risk of being done badly.

 

Before we built the internal walls we parged the external walls one block wide for airtightness at the join.  This is probably overkill as a "toothed" wall is airtight beyond the first perp if properly filled. Just airtight paint at the top before the ceiling joists go in.

 

I would be interested to know what your builder says about this.

 

Edited February 12 by Mr Blobby

[Gaf]

@Mr Blobby Ah I get you now. That was definitely me not getting it and nothing on you!

 

Definitely one I'll check with the builder about. Will report back when I know!

 

Similarly, I'd wonder about the structural stability, particularly since we're getting either solidcore or hollowcore slabs on the firstfloor.

 

 

[saveasteading]

An alternative to bonding the blocks as shown above is the use of a wall starter kit. Google that or crocodile wall tie.

Simpsons are the big name.