IWI on 9" solid wall

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The Apprentice

The Apprentice

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Doing a job and the surveyor told the customer not to use board adhesive on a9" solid wall as it attracts condensation. I can understand is issue if we weren't using insulated boards but surely with insulated boards you ain't going to get mould due to cold spots. Any advice or info I can pass to the customer to allay her fears please chaps would be appreciated.
 
He is right you are still dabbing it the fact you can't see it straight away doesn't mean it's not there, simple solution is batten it.
 
He's right , cold bridging , with insulated board you need to mushroom , the passive house fixings are very good though pricey.

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You could use a tanking product and dab insulated boards onto that as another option

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I don't dab any IWI boards, mechanically fix all the time, usually about 30p per fixing.

Was taught you want the boards tight up to the existing wall with no gap between board and wall as this will cause a moisture build up where cold air from the external wall meets the warm air from inside, similar to a failed double glazed unit with condensation in between panes
 
Even if fixed to the wall your not telling me there aren't gaps in behind, no wall flat.
What's the passive fixings paddy??



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flynnyman said:
This will cause even more problems coz this will be saturated in a few months.
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Your opinion, but if its tightly fit there's nowhere for condensation to form, also stops the direct meeting of cold air and warm air in an open void.

You want a gradual temperature change through the wall, not a sudden change
 
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Can you explain that picture then.

Where's it from? Why is it worse to have no air gap?

The info I have comes from the guy who taught me and direct from weber (Stuart I think)

The temperature wants to be a steady but straight decline to the outside wall, how can water form if there's no meeting of cold and warm air, just a steady decrease of temp through the wall

Genuine question
 
You have cold moisture penetrating through the brick so without the air gap your effectively bridging from outside to inside. The condensation occurs on the back of the insulation ( interstitial condensation) the way it forms on Windows because of the dew point. warm air hitting a cold surface etc.

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The air gap itself carries a thermal resistance so that would contribute to a reduced sudden change In temperature. Without an air gap the temp change is sudden resulting in condensation which would also lead to accelerated bridging due to direct contact.
 
So why does foil backed make it worse, this is what we use.

Can't understand why weber guy would tell me different.

His words, "most important thing with IWI is not air gap between back of board and wall"

Gunna ring the c**t tomorrow
 
OK so I have a job coming up which has a filled 50mm cavity and hopefully going to dab thermaline to come up to u values. Am I wrong in doing this?
 
Foil is absolutely none porous so condensation forms rapidly.
I'm leaning more to the idea of products like Stormdry in conjunction with these systems. When a brick is wet it loses large amounts of its U value and cold transfers quicker. Keeping the bricks dry but allowing vapour to release reduces the temperature differential at condensation point.
 
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The last boards we used were mid foil not foil backed, still vapour resistant but when I spoke to the manufacturer they told me pinning directly to the wall was fine.

Can't remember name of them
 
Priceplastering said:
OK so I have a job coming up which has a filled 50mm cavity and hopefully going to dab thermaline to come up to u values. Am I wrong in doing this?
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You'll be fine with the u value, not so sure about the wall sandwiched in between two layers of insulation, that's the same problem with ewi on insulated cavity walls. An engineering architect can give you a proper explanation of this, but as long as BC happy with it why worry
 
Just for the record we haven't had any problems with what we have done and I have returned to jobs 3/4 years later to carry out more work on properties that have IWI.

I think both methods will cause some degree of moisture, just a case of which causes less.

It was recticel & thermal one we spoke to in the past.

Why do they sell mechanically fixed wall plugs which are used to directly pin the boards to the wall
 
The mechanical fixings are for after you have dabbed them mac, your supposed to put 3 or 4 in per board, supposed to be for if there is a fire the boards don't start falling in, so I was told ......


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