Air Tight finish help!?

[richo106]

Hi

 

We are converting a bungalow (adding another floor) and aiming to get it as air tight as possible (aiming for 3/4)

 

The internal walls will be block but I have been trying to research best way to achieve air tightness. These are:

 

1. Wet plaster - plasterer says time consuming and expensive 

 

2. 5/6mm parge coat then dot and dab - this what plasterer recommends (best of both worlds)

 

3. Air tight membrane fixed to the wall with 25mm battens then PB screwed to battens

 

4. Another method that I have missed?

 

Has anyone got any advice/experience on which method is best?

 

Appreciate any feedback

 

Many Thanks

 

Edited March 9, 2022 by richo106

[SuperPav]

The problem is that while all the 3 methods you mention can work, 2 and 3 require a lot of attention to detail to avoid a lot of air movement behind the plasterboard.

If you're going to do it or oversee that it gets done properly, i.e. really picky, then that's fine.

 

Otherwise, wet plaster is the "easiest" way while just employing a plasterer.

 

 

[Russell griffiths]

You need to pay more attention to the junction areas, the area at the bottom of the new walls to the old, builder will lift his plasterboard 20mm above the floor upstairs leaving a big gap with no dot n dab, this space heading downstairs to whatever plaster finish you have down there. 

This is your week area, concentrate on these and the mass areas will be ok. 

[nod]

As above 

You can achieve perfect airtightness with Dot and dab No need Parge It’s. not worth the money 

But you do need good attention to detail Junctions sockets etc 

[richo106]

One other reason for the wet plaster options was to help with thermal mass, do you think this will make much of a difference?  
 

thanks again for all the replies very helpful! 
 

 

[joe90]

I just don’t like hollow walls so would not have dot and dab, I had cement render followed by wet plaster finish, this was specced but me after the initial quote from the main contractor and it did not alter the price!!! I can hang anything anywhere with no worries.

[MikeSharp01]

45 minutes ago, richo106 said:

thermal mass

Is that a thing? (says he lighting blue touch paper and standing well back.)

[richo106]

43 minutes ago, MikeSharp01 said:

Is that a thing? (says he lighting blue touch paper and standing well back.)

Haha I am eagerly awaiting some replies to this 

[tonyshouse]

I like wet plaster but still needs to joined to the airtightness layer in the ceiling, Unser the floor and penetrations need detailing carefully 

[nod]

2 hours ago, joe90 said:

I just don’t like hollow walls so would not have dot and dab, I had cement render followed by wet plaster finish, this was specced but me after the initial quote from the main contractor and it did not alter the price!!! I can hang anything anywhere with no worries.

We are at about 80-20 with dot ab and sand and cement 

20 years ago it was the other way round I dabbed ours in thermal boarded 

I was tempted to sand and cement the lot Cheaper option 

 

The problem I have with sound coat being used for airtightness is it’s like you have given up on trying to seal the plasterboard Which isn’t difficult with a bit of care 

 

We are plastering and tiling four houses at the moment Tgat start from 1.3 million pounds 

Three are dabbed and one is sand and cement All four will be air tested 

and have to achieve 2 or Less 

[Iceverge]

Sand cement wet plaster here followed by skim. 

 

0.31 Ach 50. Many hours of prep with airtight paint and tape beforhand however.

[joe90]

3 hours ago, MikeSharp01 said:

Is that a thing? (says he lighting blue touch paper and standing well back.)

Ha, he is new here so will not know our previous discussions on the subject, the thing is we all know what he means!, I just say “heavy” nowadays 👍

[Radian]

3 hours ago, nod said:

We are plastering and tiling four houses at the moment Tgat start from 1.3 million pounds 

Three are dabbed and one is sand and cement All four will be air tested 

and have to achieve 2 or Less 

 

Interesting, has any reason been given for the sand/cement one? I hope you can share the results of the air tests!

[Chanmenie]

7 hours ago, nod said:

As above 

You can achieve perfect airtightness with Dot and dab No need Parge It’s. not worth the money 

But you do need good attention to detail Junctions sockets etc 

@nod I’d be really interested to learn how to get perfect airtightness with dot and dab 

[nod]

48 minutes ago, Chanmenie said:

@nod I’d be really interested to learn how to get perfect airtightness with dot and dab 

A continuous line of adhesive around the perimeter of each wall Also the same with switches and socket 

Acoustic sealant needs to be used around All edges of plasterboard walls an ceilings Where they meet external block 

[Onoff]

26 minutes ago, nod said:

A continuous line of adhesive around the perimeter of each wall Also the same with switches and socket 

Acoustic sealant needs to be used around All edges of plasterboard walls an ceilings Where they meet external block 

 

How are the block joints made airtight? 

[Nickfromwales]

2 hours ago, Chanmenie said:

@nod I’d be really interested to learn how to get perfect airtightness with dot and dab 

Be careful what you say to him.....as he'll talk you into an apprenticeship!

[Nickfromwales]

12 hours ago, richo106 said:

 

2. 5/6mm parge coat then dot and dab - this what plasterer recommends (best of both worlds)

For anyone not well versed in this, and for pretty much guaranteed results, this is a good option. Fast, good airtightness, and walls can be made arrow straight.

Fortify this with tapes / membranes and you'll achieve great results.

[Chanmenie]

8 hours ago, Nickfromwales said:

Be careful what you say to him.....as he'll talk you into an apprenticeship!

😀  think I’m a bit old to start another apprenticeship, the last one I did I started in 1978 

[Chanmenie]

@Nickfromwales @nod

thanks for the tips guys, but in your opinions what is the best option for DIY on woodcrete (Isotex) blocks 

[Nickfromwales]

1 hour ago, Chanmenie said:

@Nickfromwales @nod

thanks for the tips guys, but in your opinions what is the best option for DIY on woodcrete (Isotex) blocks 

Deffo parge afaic, regardless of which woodcrete system. Just achieved 0.88 on one such build so "it can be done"  

Bolster that with Passive Purple / similar blower proof painted / brushed on ( liquid ) membrane for the tricky areas and junctions where timber meets ICF and you'll have great results. What stage are you in the build?

[Chanmenie]

44 minutes ago, Nickfromwales said:

Deffo parge afaic, regardless of which woodcrete system. Just achieved 0.88 on one such build so "it can be done"  

Bolster that with Passive Purple / similar blower proof painted / brushed on ( liquid ) membrane for the tricky areas and junctions where timber meets ICF and you'll have great results. What stage are you in the build?

Thanks Nick, so what comes after the parge ? dot and dab or screw the plasterboard direct to the woodcrete blocks.

 

we are hoping to break ground next month, had hold ups with structural engineer and planning department.

[Russell griffiths]

49 minutes ago, Chanmenie said:

Thanks Nick, so what comes after the parge ? dot and dab or screw the plasterboard direct to the woodcrete blocks.

 

we are hoping to break ground next month, had hold ups with structural engineer and planning department.

You cannot just screw to the woodcrete blocks, not unless you want a wall that is about as flat as the moon, will either need battens or dot n dab. 

[Chanmenie]

1 minute ago, Russell griffiths said:

You cannot just screw to the woodcrete blocks, not unless you want a wall that is about as flat as the moon, will either need battens or dot n dab. 

I thought you could with isotex, they are pretty flat and consistent, not like Durisol which are all different thickness

[Russell griffiths]

6 minutes ago, Chanmenie said:

I thought you could with isotex, they are pretty flat and consistent, not like Durisol which are all different thickness

All depends on what you mean by flat, they are reasonably square and true, but after you stack them 10 high and fill with concrete the surface has many lumpy bumpy sticky out bits, definitely not flat enough to screw boards to.