How to make improve older brick walls airtightness

[DeanAlan]

Hi all,

 

This forum continues to be of amazing help. I hope one day I can give something back here beyond the comedy value of my questions 😀

 

Our renovation and extension project is now at the stage where we are about to dryline. But first I need to get the MVHR installed and do what I can to up the airtightness of the whole structure. We are likely going to use something like Blowerproof of Passive Purple on the SIPs extension. I want to do something for the original house which is solid brick wall construction. We've taken all the plaster off and down to the bricks (Cambridge hand made whites I am told they are) circa 1920. Very dusty, and mortar is quite crumbly. 

 

Questions:

 

1. Before I do anything for airtightness do you think I should look to get the physical structure of these bricks/mortar in better shape? Maybe something like a parge coat?

2. Would a parge coat (if done well) bring the airtightness up to a good level?

3. Should I then passive purple or blowerproof over that or maybe the same but directly onto the bricks as they are (which I don't think I could do with a brush, would need a spray version)?

 

alternative ideas?

 

cheers,

- Dean

 

PS just searched this forum on parge and airtightness and think I might have resurfaced a massive debate. I think the key difference in my question though is the starting point - an older brick wall / mortar, not nice new blockwork. We'll be dot & dab drylining over that.

Edited July 21, 2022 by DeanAlan

[jayc89]

How do you plan to finish the walls in the original part of the house?

Repointing and wet (lime) plaster direct to the brick is probably the best bet, and the plaster acts the same as a large coat would. If you're not going to wet plaster than a parge coat would make sense, although bear in mind any mechanical fixings to your PB will penetrate the parge... Care needs to be taken around reveals, up through intermediate ceilings, around any floor joists pocketed into the walls etc. Across the top floor ceiling, or roof joists, an intelligent membrane (INTELLO etc) might be useful there.

I found GreenBuildingStore useful for this type of detail, here are a few options;

 

https://www.greenbuildingstore.co.uk/holmfirth-farmhouse-radical-retrofit-internal-wall-insulation-iwi-strategy/

https://www.greenbuildingstore.co.uk/lower-royd-retrofit-internal-wall-insulation/

https://www.greenbuildingstore.co.uk/internal-wall-insulation-cumberworth-retrofit/

[DeanAlan]

Expectation is to dot and dab @jayc89. Already have INTELLO ceiling membrane in for first floor ceiling/roof. Have laid new concrete floors - need to get the walls airtight themselves and then seal against the screed floor and the ceiling membrane as well as penetration points (SVP etc). Intemediate floor joists are new web joists on bolted wall plates. Was probably going to passive purple over those and seal to the wall membrane (parge, plaster, airtight paint, whatever I go with).

 

I had thought about wet plaster but very hard to find plasters that will do that these days.

[Ferdinand]

When I dryline I tend to do it traditionally framed out rather than dot and dab, then I include a membrane to help isolate the insulation from the ventilation, then install some sort of modest forced ventilation.