Airtightness test on a block house

cuculainn

Hi,

We are currently at the plastering stage of a block build. And also have our airtightness contractors meeting with our plasterer to coordinate how things will flow.

I plan on doing two airtightness tests.

1 when all the tape and membranes are in place but still exposed to get access to fix any leaks and

2 after all plastering second fixes are completed.


Should the airtightness test be carried out before the sand/cement coat is applied?

This will allow access to all the tape to repare. but The porous block will mean the result wont be accurate, but at least it will be possible to find the leaks in the tape/Membrane

sas

There was some debate on this here recently and I'm still of the opinion that it's pointless testing before the scratch coat.

My reasoning...

Block is very porous.

Well fitted airtightness tapes (with some mistakes\issues) will still be much tighter than the block work.

The air will take the path of least resistance and therefore leave via the block work before the tapes have the opportunity to do their job and hence you
won't be testing the tapes at all and are unlikely to identify issues.

I'm am as always open to correction here.

cuculainn

Thanks for the reply. I have heard this also, but if you do scratch coat, then you have to go and do an airtightness test, then put up your ceilings......it apparently becomes very difficult to put the skim coat on as this needs to be done very soon after the sand/cement.

Are blocks really that porous?

Also, if there are issues with the tape around windows/doors and the sand/cement is on, how can this be fixed?

Thanks for the discussion. It might help me get my head around it

One thing.....We have our cavity pumped. Would this reduce the airloss through the block much?

sas

cuculainn wrote: »

Thanks for the reply. I have heard this also, but if you do scratch coat, then you have to go and do an airtightness test, then put up your ceilings......it apparently becomes very difficult to put the skim coat on as this needs to be done very soon after the sand/cement.

The people who most commonly trot that line out are plasterers who want to get in and out and paid! My plasterer said that as long as you wet down the walls well before skimming, you'll have no problems.

cuculainn wrote: »

Are blocks really that porous?

So I'm told. Heard a story of guys testing this by chipping back plaster on a well sealed house during airtightness test and you could feel the breeze coming through the exposed block with your hand.

cuculainn wrote: »

Also, if there are issues with the tape around windows/doors and the sand/cement is on, how can this be fixed?

This one really is my personal thought... The sand and cement will hide some of it. If it's really bad I'll seal the gap between window and wall with a bead of some liquid sealant.

cuculainn wrote: »

One thing.....We have our cavity pumped. Would this reduce the airloss through the block much?

No idea.

cuculainn

Thanks for the reply SAS.

Its the one area (including insulation and Ventilation!)I want to have right so I think I will get the external walls scratch coated before the test. That might do the job

Radonman

To answer a few of your questions -
Yes, blocks are very porous - we have had a situations where the air tight membrane is fitted perfect (smoke pencil tested) and we could not pump air into the house, solution was to scratch coat and insulated board (the blockwork was brutal in this house).
Beads help but is not an air tight solution.
Issues with tapes around windows after scratch should be the installers problem, get him to hack it off, re apply membrane and re-plaster or as the previous said air tight silicone (but this is not ideal or permanent).
Also try to have the installer present when it is tested to do any odds and ends that may be found - there will be a big difference in the 2 tests but the more you get right on the first test the better for you

cuculainn

Radonman wrote: »

To answer a few of your questions -
Yes, blocks are very porous - we have had a situations where the air tight membrane is fitted perfect (smoke pencil tested) and we could not pump air into the house, solution was to scratch coat and insulated board (the blockwork was brutal in this house).
Beads help but is not an air tight solution.
Issues with tapes around windows after scratch should be the installers problem, get him to hack it off, re apply membrane and re-plaster or as the previous said air tight silicone (but this is not ideal or permanent).
Also try to have the installer present when it is tested to do any odds and ends that may be found - there will be a big difference in the 2 tests but the more you get right on the first test the better for you

Hi Radonman,

Thanks for the reply, so in the houses where you have tested without the blocks plastered were you able to find the leaks in the tape/membrane?
That is really what I am looking to achieve at this test

BTW the blockwork is very good in the house

sas

Radonman wrote: »

we have had a situations where the air tight membrane is fitted perfect (smoke pencil tested) and we could not pump air into the house

If you couldn't pressurise the house, how do you know you were testing the membrane\tapes i.e. how could you prove they were fitted perfectly?

Radonman

sas wrote: »

If you couldn't pressurise the house, how do you know you were testing the membrane\tapes i.e. how could you prove they were fitted perfectly?

We were still able to pinpoint the weak areas of the tape and jointing as we ran around every window,door, joints etc (this was a very detailed test as you can imagine when we could not pressurise the house) with a smoke pencil, all these were repaired. The air was still leaking a such quantities that the assumption was that is was the block work hence the remedial works explained earlier

beyondpassive

+1 to SAS and Radonman. While testing at slabbing/second fix is the most opertune time, often its no harm to get a preliminary test done before the drywall plaster just to identify the bigger leaks from plumbing and electric, this dosent need to be a full test, it can just be done manually at a pressure of 50 pascals.It also eliminates any major surprises or disapointments at the main test.

soldsold

What I did was to test the house after applying all airtightness measures but before plasterboarding, and the test showed up a number of problem areas that couldn't be fixed after plasterboarding/ skimming:

- Gap between side by side concrete lintols over 2 windows - I had assumed it was a solid mortar bed and concrete block over them but was open to the cavity.

- Gap under sliding door - would have probably been fixed when laying floors though.

- Loads of gaps around window tapes where the tapes had pulled away from the solitex membrane that I was using to close the cavity.

- Gap where hole for alarm cable/ external speakers had been drilled and not filled.

- 1 gap between hollowcore slabs even though solitex membrane had been applied.

- Foamed holes where the spray can foam wasn't sealing properly.

- Small gaps (seen with thermal imaging camera) at all 4 corners of all triple glazed velux windows, and all hinges on triple glazed windows. As the song says, I wasn't expecting that.

- Bits that were missed with airtightness tape

Gradually the airtightness tester was able to generate more and more pressure as I fixed the leaks which incidentally were easy to see on the thermal imaging camera but also easy to feel with my hand as the tests were done a couple of months back when it was cold outside and cold air was being drawn in.

Anyway, my opinion is to test before plastering which will find major leaks, then test again after plastering to make sure all is ok. Pretty much in line with what the general advice is.

On the subject of blocks being too porous to allow any meaningful test, this is true, and the weak points on my build was more the mortar bed gaps rather than through the blocks. However even though I couldnt get anywhere near 50 pascals, the tape weaknesses showed up clearly.