Airtightness of blockwork

[JackofAll]

Apart from floor to wall junction, what other junctions need painting, where internal walls meet external? 

[MikeGrahamT21]

Liquid membrane on all junctions, parge coat on the rest

[JackofAll]

1 hour ago, MikeGrahamT21 said:

Liquid membrane on all junctions, parge coat on the rest

Thanks Mike, does that include the top row of blocks that meet the roof or does the air tight membrane at ceiling level take care of that?

[MikeGrahamT21]

So anything which has the potential to move and crack needs it, so think along the lines of wall plate timber against blockwork interface, this needs the liquid membrane as the materials will expand at different paces and inevitably crack, a stretchy liquid membrane will sort this permanently. Covering with airtight membrane from the roof could lead to air getting behind the membrane. 

[JackofAll]

Thanks @MikeGrahamT21, I take it sand/cement/skim are not airtight enough if you parge coated first

 

[nod]

4 hours ago, MikeGrahamT21 said:

Liquid membrane on all junctions, parge coat on the rest

Parge is a waste of time and expense 

By using it Have you given up on trying to seal the dot and dab 

[MikeGrahamT21]

My personal preference is to wet plaster with bonding coat and then multi finish but it does take time to dry, I’ve never been a fan of dot and dab, too much that you can’t see can go wrong

[MikeGrahamT21]

2 hours ago, JackofAll said:

Thanks @MikeGrahamT21, I take it sand/cement/skim are not airtight enough if you parge coated first

 

as above, bonding coat/hardwall and skim is absolutely fine for airtightness

[twice round the block]

Hard plastering is coming back into fashion after 30 year's of dot and dab and the failings it has.

Problem being lot's of the old tradesmen don't exist anymore.

[Mike]

11 minutes ago, twice round the block said:

Hard plastering is coming back into fashion after 30 year's of dot and dab

Long overdue, IMHO.

[Mattg4321]

3 hours ago, nod said:

Parge is a waste of time and expense 

By using it Have you given up on trying to seal the dot and dab 

Any tips on what to look for/how to properly seal the dot and dab? Just a matter of sealing all round the perimeter of each board?

[MikeGrahamT21]

1 hour ago, Mattg4321 said:

Any tips on what to look for/how to properly seal the dot and dab? Just a matter of sealing all round the perimeter of each board?

according to manufacturers specs, yes. But a lot can happen in the 2.8m2 of area behind that one board

 

however aircrete blocks are very common background to be sticking on to, they shrink and crack very easily resulting in air leakage. Even denser aggregate blocks can be hard to get the mortar to make a perfect seal, which is where the parge coat came in, but it’s not thick enough to withstand shrinkage.

 

For me, avoid D&D at all costs

Edited December 17, 2023 by MikeGrahamT21

[nod]

9 hours ago, Mattg4321 said:

Any tips on what to look for/how to properly seal the dot and dab? Just a matter of sealing all round the perimeter of each board?

Just stress to your dabbers that it needs to be sealed properly 

It really isn’t difficult A continuous line of adhesive around every perimeter and frame Every socket and pipe 

As I’ve stated before If you put an airtight layer on Your dry liners won’t bother to do the above It would do any harm to put a Parge coat on But it won’t make any difference to airtightness But if you do Call it by the name on the bag Sound block

 

As a business I still use a couple of thousand bags per year Mainly housing associations Always for sound transfer reasons 

 

15+ years ago we used it on virtually everything Due to block work being left snotty with joints missing 

Now they would get through there pre plaster inspection 

[JackofAll]

11 hours ago, twice round the block said:

Hard plastering is coming back into fashion after 30 year's of dot and dab and the failings it has.

Problem being lot's of the old tradesmen don't exist anymore.

Afaics It's still the main way of plastering block walls here.