Airtightness - Wrapping Wideslab

rampantbunny

Hi all. I'm planning a direct labour build, and have recently been getting some quotes in for both hollowcore and wideslab.

In order to achieve a level of airtightness, it's recommended by many on boards to wrap the end of hollowcore in a membrane. I say 'end' as I'm not sure if this wrapping is to extend all the way around to the solid face\side of the slabs too.

If it is just the ends that are wrapped, is the same measure required for wideslab?
Wideslab comes in sections twice the width of hollowcore (2400 vs 1200) therefore less joints to fill. Plus wideslab doesn't have holes at the end (although holes in hollowcore can be filled).

Considering the additional work of installing the membrane, watching over it as the concrete product is installed, lapping and attaching the membrane to the wall, and possible education of plasterer - I'm wondering if there is another way.

Note that I did not say "better" - but for a project where you have maybe 6 joints at most on your longest run, is membrane a bit overkill? If the wideslab was bedded down onto some mortar at the end that meets the cavity, and the joints between sections sealed with foam - would that suffice? Maybe get some plaster up underneath the slab where it meets the downstairs internal leaf.

Interested to hear opinions.

Curious Geroge

Hi rampantbunny, I'm just finished laying the holicore and we had the ends sealed. We then got the plaster to bed them when laying. The thought is that we limit the movement of air. I have plans to put an airtight membrane on the roof and around windows and doors but it would be great to get some pictures of this work in progress and any advice on doing this.

Also, should we be taping the outer wall where the ceiling meets the holicore and floor meets the raft ?

rampantbunny

Curious Geroge wrote: »

Hi rampantbunny, I'm just finished laying the holicore and we had the ends sealed. We then got the plaster to bed them when laying. The thought is that we limit the movement of air. I have plans to put an airtight membrane on the roof and around windows and doors but it would be great to get some pictures of this work in progress and any advice on doing this.

Also, should we be taping the outer wall where the ceiling meets the holicore and floor meets the raft ?

Lol...Hi George - not sure my original post came across as it should have. You see, I'm a bit clueless also so I'm not the person to advise you on what needs to be taped etc. If you have an architect or other professional on your project, then I'd turn to them for advice on the proper detail.

I've taken my own advice on this, but my architect isn't very well versed in these matters so I'm also here looking for guidance. Hopefully someone with more knowledge than us both combined will be along shortly

MicktheMan

The reason for wrapping the slab is not just to seal the joints between the slabs but is really to continue the airtightness barrier from the wall below, around the intermediate floor and up to the wall above. It is relatively simply done once understood. I normally demonstrate on site to all involved what's involved.

Note if this is not done properly:
I have just, this afternoon, returned from a recently built architecturally designed bungalow with a concrete flat roof where I tested the house for air leakage. The owner and architect were present. The architect had never witnessed an airtightness/leakage test before:eek:. The roof leaked like a sieve simple because there were no airtightness details specified and, in reality, not understood by the architect or builder. The owner was perplexed because eventhough the house was well with the building regs, it could have been soo much better with a little preplanning and preparation. Unfortunately, this is NOT an isolated case:mad:

mfceiling

http://www.boards.ie/vbulletin/showpost.php?p=60301893&postcount=21

http://www.boards.ie/vbulletin/showpost.php?p=60349139&postcount=23

http://www.boards.ie/vbulletin/showpost.php?p=66009136&postcount=859

If you want to know what to do when wrapping the wideslab then SAS was pretty much an expert on this.

rampantbunny

MicktheMan wrote: »

The reason for wrapping the slab is not just to seal the joints between the slabs but is really to continue the airtightness barrier from the wall below, around the intermediate floor and up to the wall above. It is relatively simply done once understood. I normally demonstrate on site to all involved what's involved.

My engineer has specified that the slabs be strapped (steel straps) to the outside face of the internal leaf. Not sure why, but in any case this will compromise the wrapping procedure, as I'll have to cut slots in the membrane to accommodate these.
I suppose I could fold the membrane over the top side of the slab (as normal), and before the first course of block work goes down, install the straps. I'll have to nail through the membrane on the top side to attach the strap, but as this will be under a block I imagine it would be ok...

Have you ever seen the airtightness detail done differently though Mick? I imagine sealing the joints, plus ensuring* no leakage above or below the slab results in the same net effect as wrapping?
I caveat 'ensuring' because that won't be known until test time and maybe it is more difficult to get it right without a membrane.

rampantbunny

mfceiling wrote: »

http://www.boards.ie/vbulletin/showpost.php?p=60301893&postcount=21

http://www.boards.ie/vbulletin/showpost.php?p=60349139&postcount=23

http://www.boards.ie/vbulletin/showpost.php?p=66009136&postcount=859

If you want to know what to do when wrapping the wideslab then SAS was pretty much an expert on this.

Cheers mfceiling. Read sas posts with interest and noted the detail. Just wondering if there is another method to accomplish the same thing.

Am I correct in saying the aim is to stop air ingress between the joints in the slab, and the junction between slab and block work (or is there more)?

If we rendered the outside of the internal leaf, from the block underneath the slab to the block above the slab, would this possibly do the job? (Uncle is plasterer and would be more comfortable doing this than installing membrane, attaching to wall etc.)
If slabs encroach too much into the cavity then this exercise would be difficult, but just putting it out there.



Edit:
One thing I haven't seen, is whether the membrane is continued around the corners onto the long side of the slab? Don't the slabs usually stop short of the internal leaf on the long sides, allowing the internal leaf blockwork to continue unbroken?

MicktheMan

rampantbunny wrote: »

Have you ever seen the airtightness detail done differently though Mick? I imagine sealing the joints, plus ensuring* no leakage above or below the slab results in the same net effect as wrapping?
I caveat 'ensuring' because that won't be known until test time and maybe it is more difficult to get it right without a membrane.

I have seen it done differently but with very poor results. I always try to recommend what is buildable on site with as few "ifs" and "buts" as possible (i.e. caveats).

MicktheMan

rampantbunny wrote: »

If we rendered the outside of the internal leaf, from the block underneath the slab to the block above the slab, would this possibly do the job? (Uncle is plasterer and would be more comfortable doing this than installing membrane, attaching to wall etc.)
If slabs encroach too much into the cavity then this exercise would be difficult, but just putting it out there.

Not a great detail as you are discontinuing the air tight layer and leakage will occur through the inner leaf blockwork/mortar joints.

MicktheMan

rampantbunny wrote: »

My engineer has specified that the slabs be strapped (steel straps) to the outside face of the internal leaf. Not sure why, but in any case this will compromise the wrapping procedure, as I'll have to cut slots in the membrane to accommodate these.
I suppose I could fold the membrane over the top side of the slab (as normal), and before the first course of block work goes down, install the straps. I'll have to nail through the membrane on the top side to attach the strap, but as this will be under a block I imagine it would be ok...

Strapping should not pose a problem as any penetrations can be readily repaired

MicktheMan

rampantbunny wrote: »

Edit:
One thing I haven't seen, is whether the membrane is continued around the corners onto the long side of the slab? Don't the slabs usually stop short of the internal leaf on the long sides, allowing the internal leaf blockwork to continue unbroken?

Depends on engineers specifications and if there is enough room to plaster between the innerleaf and slab

rampantbunny

MicktheMan wrote: »

Not a great detail as you are discontinuing the air tight layer and leakage will occur through the inner leaf blockwork/mortar joints.

I'm guilty of labouring the point, but no harm exhausting the possibilities so I'll have one final push Mick if you don't mind...
If the inner leaf was plastered to the ceiling (under the slab) and from the slab up on the first floor would this leakage occur?

MicktheMan wrote: »

Strapping should pose a problem as any penetrations can be readily repaired

I'm reading this as "should not pose a problem.."
Would you put the straps on top of the membrane after it is folded on top of the slab, or cut through the membrane?

MicktheMan

rampantbunny wrote: »

I'm guilty of labouring the point, but no harm exhausting the possibilities so I'll have one final push Mick if you don't mind...
1. If the inner leaf was plastered to the ceiling (under the slab) and from the slab up on the first floor would this leakage occur?
2. I'm reading this as "should not pose a problem.."
3. Would you put the straps on top of the membrane after it is folded on top of the slab, or cut through the membrane?

1. Yes, a lot
2. Correct
3. Depends on engineer's spec

rampantbunny

MicktheMan wrote: »

1. Yes, a lot
2. Correct
3. Depends on engineer's spec

I should have be clear in previous post and wrote that the internal render would go on in addition to the external render at end of slab (post #7), but I imagine at this rate it makes no difference and the only real solution is membrane, full stop.

Cheers Mick.

BarneyMc

I copied below from one of the old links above. I've added an alternative in red:

The membrane is fixed to the wall inside.
The membrane travels up the wall and then turns towards the cavity travelling underneath the hollowcore.
The membrane is now brought up around the hollowcore (in the cavity) and back inside above the hollowcore.
The upstairs block work is completed on top of the membrane.
The membrane is then fixed to the inner surface of the inner leaf of blocks OR could it be brought back onto the first course of blockwork and out into the cavity where it could be trimmed?

I only ask this as it might prevent builders and other tradesmen from tramping over it. Are there any drawbacks to doing this?

rampantbunny

BarneyMc wrote: »

I copied below from one of the old links above. I've added an alternative in red:

The membrane is fixed to the wall inside.
The membrane travels up the wall and then turns towards the cavity travelling underneath the hollowcore.
The membrane is now brought up around the hollowcore (in the cavity) and back inside above the hollowcore.
The upstairs block work is completed on top of the membrane.
The membrane is then fixed to the inner surface of the inner leaf of blocks OR could it be brought back onto the first course of blockwork and out into the cavity where it could be trimmed?

I only ask this as it might prevent builders and other tradesmen from tramping over it. Are there any drawbacks to doing this?

I'm no expert barney, but I imagine there might be a slip plane issue. Wouldn't the first block be pretty much isolated by this wrapping method, both underneath and above?

BarneyMc

rampantbunny wrote: »

I'm no expert barney, but I imagine there might be a slip plane issue. Wouldn't the first block be pretty much isolated by this wrapping method, both underneath and above?

Yes, good point bunny. Let's see if anyone can throw some light on this.

esox28

[/IMG]photobucket.com/albums/q775/esox25/phone050_zpsaec94699.jpg[/IMG]

what i done was to lay down some solitex roofing membrane taped the joints ready to recieve the slabs



slabs in place ready for screed





screed pored with membrane tucked under the screed retainer, and as you can see the membrane is ready to be pulled up and over the slap/screed ready for the first course of blockwork of the ff.



here you can see the slap membrane rising up onto that first course, wired mesh and steel nailed into position ready for plastering....nearly.


hope this is of some use to op and others, big thanks to the guys on C&P who helped me along the way....still along ways off yet.:)

BarneyMc

Great pics esox28 and thanks. Is is really necessary to use the SOLITEX PLUS? I heard a radon barrier sheath would be fine and less expensive.

hexosan

Was going to look at block & beam flooring and was wondering would it be any easier/harder than Hollowcore & wide slab to get airtight at the wall junction.

rampantbunny

Hi esox28. Hope the build is going well. Fantastic post, it will be very helpful.

I originally started the thread to see if there was another way to achieve the same airtightness result. I thought a full wrap might not be necessary for a wider slab...but based on Micks responses it looks like this is the (only) way to do it.

PM sent with some follow up questions if you have the time.
If you have, and my questions make sense, we might update the posts above for all.

rampantbunny

hexosan wrote: »

Was going to look at block & beam flooring and was wondering would it be any easier/harder than Hollowcore & wide slab to get airtight at the wall junction.

Not familiar with block and beam installations at all, but don't the beams sit on the inner leaf blockwork, thus a break in the blockwork is required?
If so, then you'd have the same issues as with other slab installations. The wrap would solve the issues for you, but you'd have a lot more joints to fill between blocks\beams - unless a screed is laid directly on top. But again, not familiar with the details here.

BarneyMc

hexosan wrote: »

Was going to look at block & beam flooring and was wondering would it be any easier/harder than Hollowcore & wide slab to get airtight at the wall junction.

I've seen the use of these type of hangers as an alternative.

There still might be a need to fix tapes, etc. around the places where you've hung the brackets?

hexosan

Block and beam has been ruled out got prices bac today and its approx 60% more expensive than Hollowcore from two suppliers. Both said straight off the bat they wouldn't compete with Hollowcore suppliers.

archtech

Block and beam is best suited to renovation work where access is restricted. In terms of air tightness it wouldn't be of any great advantage either.

hexosan

archtech wrote: »

Block and beam is best suited to renovation work where access is restricted. In terms of air tightness it wouldn't be of any great advantage either.

Exactly what both suppliers said.

BarneyMc

Very interesting on both cost and airtightness. I'm using hollowocre myself so that's good news!

hexosan

BarneyMc wrote: »

Very interesting on both cost and airtightness. I'm using hollowocre myself so that's good news!

It's back to Hollowcore for me, can I ask what price per M people are paying of their Hollowcore.

rampantbunny

hexosan wrote: »

It's back to Hollowcore for me, can I ask what price per M people are paying of their Hollowcore.

Email on the way.

BarneyMc

hexosan wrote: »

It's back to Hollowcore for me, can I ask what price per M people are paying of their Hollowcore.

Approximately €5k for 130 square meters.

hexosan

BarneyMc wrote: »

Approximately €5k for 130 square meters.

I've a quote from a local supplier for just under €34/m including vat. Look like your paying €38.50. Ill PM you the details to see if we're like for like

BarneyMc

hexosan wrote: »

I've a quote from a local supplier for just under €34/m including vat. Look like your paying €38.50. Ill PM you the details to see if we're like for like

Haven't got the full quote yet but will ask my PM when I speak with him next. I'm basing it on the ground floor slab costs which came in at €5k.

Just getting back to the SOLITEX membrane - is this really necessary or would a standard heavy duty plastic sheet be ok to use when wrapping the slabs?

BryanF

BarneyMc wrote: »

Just getting back to the SOLITEX membrane - is this really necessary or would a standard heavy duty plastic sheet be ok to use when wrapping the slabs?

radon membrane would be best IMO - have you read through Sas's posts on the topic, very comprehensive, with photos or so i remember

BarneyMc

BryanF wrote: »

radon membrane would be best IMO - have you read through Sas's posts on the topic, very comprehensive, with photos or so i remember

Yes indeed, this post refers to it and has the link.

SAS however also used the SOLITEX. I don't know much about these membranes but I suppose a radon membrane is as good as any?

tred

BarneyMc wrote: »

Yes indeed, this post refers to it and has the link.

SAS however also used the SOLITEX. I don't know much about these membranes but I suppose a radon membrane is as good as any?

if you are wrapping it, then just remember whats coming after, blocks, cement, tears can happen. Have to say the radon barrier is a lot stronger than some of the felts out there.

BryanF

tred wrote: »

the radon barrier is a lot stronger than some of the felts out there.

exactly

sas

2 concerns with radon barrier:

1. On the assumption that they are all some form of plastic sheeting, they are difficult to create neat corners with, REALLY difficult.

2. While you mesh the material onto the wall, I see it as advantageous that mortar will bond to solitex much better than to a plastic radon membrane. You run less of a risk of a gap between the membrane and the mortar forming. Not sure how big a deal it is but I'd be wary.

My 2 cents.

BarneyMc

sas wrote: »

2 concerns with radon barrier:

1. On the assumption that they are all some form of plastic sheeting, they are difficult to create neat corners with, REALLY difficult.

IS this not the same with the SOLITEX?

sas wrote: »

2 concerns with radon barrier:

2. While you mesh the material onto the wall, I see it as advantageous that mortar will bond to solitex much better than to a plastic radon membrane. You run less of a risk of a gap between the membrane and the mortar forming. Not sure how big a deal it is but I'd be wary.

If the radon barrier is trimmed to a few inches and then tape applied, would the mortar not then stick ok to the tape?

sas

BarneyMc wrote: »

IS this not the same with the SOLITEX?

Having worked with both I can say that Solitex is far easier to work with. It's less rigid with it effecively being a fabric.
I would question how robust the membranes really are. I had 2 types on site. The expensive RMB400 which is very very robust
but it would be easier fold the corners out of sheet metal! The cheaper black plastic version which I found tears easily i.e. you accidently nick the edge of it and the tear will travel.

BarneyMc wrote: »

If the radon barrier is trimmed to a few inches and then tape applied, would the mortar not then stick ok to the tape?

That might be a fair point. I don't know because tape didn't come into the equation for me.

Again, 2 cents worth. Fortunately I don't have to care about this sort of thing anymore

BarneyMc

Hard to know which to go for

tred

i see the felts getting torn and in poor condition in a few jobs i had a look at...thats why i thought the radon would be a good alternative as well..

sas

What build method are we talking about here, cavity?

BarneyMc

sas wrote: »

What build method are we talking about here, cavity?

Yes, I am anyway - 250mm cavity.

sas

BarneyMc wrote: »

Yes, I am anyway - 250mm cavity.

Ok, what is the detail in your case once the hollowcore in place?

Is it the case that you pour a screed that runs as far as the edge of the cavity i.e the screed stops flush with the cavity side of the inner leaf?

The you would wrap your membrane over this screed and your upper block work sandwiches the membrane onto the screed?

Bear with me here...

BarneyMc

sas wrote: »

Ok, what is the detail in your case once the hollowcore in place?

Is it the case that you pour a screed that runs as far as the edge of the cavity i.e the screed stops flush with the cavity side of the inner leaf?

The you would wrap your membrane over this screed and your upper block work sandwiches the membrane onto the screed?

Bear with me here...

Screed will come much, much later in the build.

The 'plastic' will wrap around the hollowcore and be pulled on top of the slab and into the building. The blocks will then be built on the plastic. At some stage the plastic will then be fixed to the inside of the inner cavity wall so it sits up off the slabs.

sas

BarneyMc wrote: »

Screed will come much, much later in the build.

The 'plastic' will wrap around the hollowcore and be pulled on top of the slab and into the building. The blocks will then be built on the plastic. At some stage the plastic will then be fixed to the inside of the inner cavity wall so it sits up off the slabs.

Ok, you went a different route on the screed than I did. No potential let off for you!

Good luck with it.

rampantbunny

sas wrote: »

Ok, you went a different route on the screed than I did. No potential let off for you!

Good luck with it.

Anyone else think that was a bit of a cliff hanger?
I was almost holding my breath

BarneyMc, my screed will be installed just as yours. But the minute the first row if inner leaf blocks is in place, I'll be out with some sort of tape to fix the membrane to the wall. Even if i use solitex and it doesn't get damaged by foot fall etc, I don't want to be sweeping mortar from behind it\off it later..
The lads on site will think I've lost the plot no doubt.

[Edit] if I'm quick enough, I'll fold the membrane over the top of the block slighty, but not fully - but just enough so that next block holds the membrane in place. Easier said than done I'm sure.

BarneyMc

rampantbunny wrote: »

BarneyMc, my screed will be installed just as yours. But the minute the first row if inner leaf blocks is in place, I'll be out with some sort of tape to fix the membrane to the wall.

Yes was thinking of that myself... fit it early to the wall so there's little or no time to damage/dirty it but do you think the tape will stand the weather or is that just a temporary fix?

This is assuming you don't get a chance to double it back on the 1st course of blockwork.

rampantbunny

BarneyMc wrote: »

Yes was thinking of that myself... fit it early to the wall so there's little or no time to damage/dirty it but do you think the tape will stand the weather or is that just a temporary fix?

This is assuming you don't get a chance to double it back on the 1st course of blockwork.

Not sure barney. I haven't handled any of the tapes to get a feel for what they are capable of. Saying that, I haven't handled solitex or many radon barriers either.
But whatever I choose, it will be temporary until I can fix the membrane to dried\set block work properly (expanded metal\nails).

Great if the membrane could be taped to the top surface of the inner leaf blocks, ready to be sandwiched under the next course.
But I can't get comfortable with the idea of this slip layer both above and below that first course of blocks (even if I tape the membrane as near to the edge of the block as possible.
You posted this detail earlier and I haven't seen any answers to it yet.

If you do use a radon barrier and it does get damaged, there's nothing stopping you fixing another section of membrane on top with airtight tape. You'd have to hope the damage was reparable though.

sas

To close the loop on where I was going....

In my case I poured my screed before the upstairs block work started.

That resulted in a perfectly smooth surface onto which we folded the membrane.

When the block work began a mortar bed (say 10 - 15mm) was laid on the membrane (naturally enough) and then the blocks were placed on that mortar i.e. regular block laying.

At this point about 6 inches of membrane was still visible inside as the block work rose.

This membrane ended up pretty much in tatters despite my best efforts.

I did still fold it up the wall and we did plaster over it and down to the floor. We had no leakage at that point during the test.

I do have a theory though.

The mortar bed referred to above will be airtight on the assumption no gaps were left in it.

I could have trimmed off the visible membrane completely (i.e. not brought it up the wall).

When the plastering occured if you plaster to the floor it closes the leakage point
- The membrane is connected to the morter bed
- The mortar beds connected to the plastering
- Oh hear the word....

A passive house owner I know actually did this and it worked out for him.

It's not relevant to most of you as you appear to be laying the screed after block work.

rampantbunny

Interesting Sas , and thanks for closing the loop as you say.
A question or two to follow up since your mind is in problem solving mode.

sas wrote: »

In my case I poured my screed before the upstairs block work started.
That resulted in a perfectly smooth surface onto which we folded the membrane.

Couldn't the same smooth surface be achieved by putting a mortar bed (smooth) down on the ends of the slabs, before folding over the membrane?
Same result as yours but screed comes later.

sas wrote: »

I do have a theory though.... mortar bed will be airtight on the assumption no gaps were left in it.

When the plastering occurred if you plaster to the floor it closes the leakage point
- The membrane is connected to the mortar bed
- The mortar beds connected to the plastering
- Oh hear the word....

A passive house owner I know actually did this and it worked out for him.

If plastering to the floor upstairs closes the leakage point: Lets say you have...

• the slabs bedded down onto a mortar bed
• plaster to the underneath of the slab (even curving some of this plaster from the inner leaf block and slab joint across the under-face of the slab)
• the joints between the ends of the slabs well sealed.

- see pic.

What does the airtightness membrane provide in this case? Continuity? - but does the plaster not do this?
Earlier posts in this thread indicate that there would be leakage with plaster (not calling anyone out on this btw).


In relation to sealing the joints at the ends of the slabs; they could be foamed, or a piece of membrane taped (using airtight tape) to the corners of the slabs just before they are installed, ready to be taped to the neighboring slab. Similar to using a complete membrane, but just used in places where slabs meet.

I'll leave it at that. I'm on the path of 'there has to be many ways to skin this cat'. Some more labor intensive than others, some requiring aftercare to protect membrane...but I'll just pick one nearer the day and move on.