Air tightness.

[Big Jimbo]

Would 12.5mm plasterboard and 3mm skim with no penetrations considered airtight ?

[ProDave]

No

[Big Jimbo]

@ProDave well wet plaster on a wall is considered to be airtight ? So why is 3mm of wet plaster not considered to be ? Is it to do with the thickness ?

[ProDave]

How will you seal the joint between the PB and the floor for instance?  What about avoiding making a "plasterboard tent" open to cold air from the loft? What level of air tightness are you hoping to achieve?  Passive house?  Just scrape through building regs?

 

To me the "normal" is a proper air tight layer e,g, a membrane properly taped.

[Big Jimbo]

Well, first of all by ensuring that the dot and dab is done properly, with a continuous bead of plasterboard around the perimeter edge for starters. Can't put a membrane on a block wall. 

What i am interested in is the fact that people are always harping on about wet plaster, only way to go, etc.  So, back to the question of how thick does plaster need to be to be considered airtight ? forget the edge, and the penetrations for the purpose of the question.

[JohnMo]

YES - but

 

You don't need any plaster, as the plasterboard itself is airtight enough.  But doesn't mean you will have an airtight house.  Just the plasterboard will be airtight.

[Big Jimbo]

Cheers @JohnMo That was the info i was after.

[Nick1c]

Doesn’t covering the blockwork with a cement slurry do the job?

[nod]

9 hours ago, Big Jimbo said:

@ProDave well wet plaster on a wall is considered to be airtight ? So why is 3mm of wet plaster not considered to be ? Is it to do with the thickness ?

Basically wet plaster isn’t completely airtight Dot and dab if done correctly is just as airtight as wet plaster 

The feed back I get from wet plaster is it can feel quite cold in comparison 

 

As with our first build I will do all the plastering myself and could do wet plaster or dot and dab Wet plaster being much cheaper But I’ll dot and dab and skim again Times have moved on 

[joe90]

2 minutes ago, nod said:

Basically wet plaster isn’t completely airtight

I find that strange (if all the other bits are done right). Why do you say that? I agree that dot and dab has moved on (if done correctly). I personally don’t like the “feel” (hollow when tapped).

[jayc89]

Having fitted IWI to our house, I much prefer wet plaster. Both from a "feel" POV but also not having to faff about with wall hangings other than wall plugs. An insulating plaster could have been used (like hemp, which would have also been breathable), which would have left us with "solid" walls, but it would have taken up 2x the floor space and more than double the cost. I guess it's a necessary evil given we couldn't use EWI.