Airtightness of concrete block walls

[Adam Harper]

A few weeks ago I was discussing the airtightness of a very large warehouse type building I'm working on with my Project Manager (of some 30 years industry experience).

His view (which in my view is incorrect), is that a double skin dense block work wall which is painted on the inside will provide a good level of airtightness. There is no internal plaster or dry lining, the blocks are simply spray painted.

Is he talking rubbish or is there some truth to this?

Can anyone point me to any guidance or research on the airtightness of painted block work?

[Mark Siddall]

Adam,

Two questions:
1) What do you want to achieve?
2) How does he define “good”?

I hope the answer to 1 would agree with AECB Silver/Passivhaus standards. …If that's the case then the Project Manager's “good” solution is pretty much doomed to failure.

However, if you are aiming for something that satisfies the Building Regulations then you may have a chance (it all depends upon what the 'paint' is).

…What I can say is, without a great deal of research and investigation (including reviewing test results) I would not use or advise the use of this technique on any of my projects.

Hope this helps,
Mark

[Graeme Williamson]

Hi there. Not specifically a response to the original question but hopefully fits within the topic generally. We’re designing a new build watersports facility with external walls built of concrete block with EWI. The airtightness layer internally will be wet plaster on hard. The internal walls will also be concrete block and my question is, where the internal walls meet the external walls, do the internal walls all have to be plastered also to maintain the airtightness layer, or could they be unplastered? I looked at the Passivhaus Trust Good Practice guidance on airtightness and I don’t think it addressed that specific use case so if anyone knows where to find reliable guidance on that or can assist, I’d be grateful. Thanks. Graeme

[Grant McCowan]

Hi All – Also adding a question.  We have a domestic retrofit of a terraced two storey house built in the 90’s consisting of an outer leaf of standard 7N/sqmm block rendered to the rear with natural stone and Thermalite to the front.  The proposed EEMs include: new triple glazed windows, MVHR and improved insulation and airtightness via two measures: injected polystyrene beads to the cavity behind the rendered blockwork and internal wall insulation to the front to retain the cavity behind the north facing natural stone facade.  Any experience that can be shared on the baseline porosity of Thermalite block and the potential upgrade in air tightness as a result of filling the cavity with polystyrene beads would be appreciated.

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