Dot Dab with IWI

[Gaf]

@nod  Out of curiosity, when you mentioned not needing the parge coat, is that anything to do with needing to allow some external air to get in behind the sealed plasterboard to allow any moisture to move outward (externally)? Is there a risk of trapping moisture if there is a parge coat and then fully sealed plasterboard over that?

[Gaf]

1 minute ago, Iceverge said:

Those are K values and don't change with the thickness. You're stuck with what you have for a given material.

 

U values change with thickness alright. Thicker is a lower number which means less heat loss. 

 

What's in the 150mm cavity at the moment? 

 

 

 

 

Also what are your ultimate priorities here, room size, actually house performance or theoretical house performance? 

 

 

 

Currently EPS beads in cavity.

 

As it’s a new build I wanted my cake and wanted to eat it too. Now that the walls are up, I’m having to prioritise meeting building regulations for certification sign-off (wall u-value 0.18), followed by maintaining originally planned room sizes. Are building regs in the theoretical category? 

[nod]

6 hours ago, Gaf said:

@nod  Out of curiosity, when you mentioned not needing the parge coat, is that anything to do with needing to allow some external air to get in behind the sealed plasterboard to allow any moisture to move outward (externally)? Is there a risk of trapping moisture if there is a parge coat and then fully sealed plasterboard over that?

No 
Nothing to do with that 

years back We would parge everything Sand and cement then the more convenient bagged stuff (Sound coat) Mainly due to snotty block work

The block work would be so bad that you could climb up walls and see into cavities 

About 15 years ago All at once BC clamped down on this and Brickies where paid an extra £1 m2 to point and bar rub all joints 

The housing association jobs and commercial jobs carried on doing both for a couple of years 

But now only self builders do it 

It’s one of those things that came in when sites went from wet plaster base coat to dot and dab 

We still use it But for sound deadening 

As I’ve said on many occasions 

If you tell your dryliners that it’s for airtightness They won’t bother sealing anything 

 

 

[Gaf]

On 28/12/2024 at 21:32, nod said:

Every wall should look like this Real basic stuff 

 

Do you place a band of adhesive running down the wall where each board will meet (e.g. attached, pink lines)? Sealing behind each board? Or is it the bands of adhesive are just needed at the floor, ceiling, and wall junctions, and around fixings (sockets)?

[nod]

59 minutes ago, Gaf said:

 

Do you place a band of adhesive running down the wall where each board will meet (e.g. attached, pink lines)? Sealing behind each board? Or is it the bands of adhesive are just needed at the floor, ceiling, and wall junctions, and around fixings (sockets)?

No

Just the  perimeter 

[Gaf]

Final post on this (hopefully). Got a meeting on site. All very amicable. It was agreed to provide full sealant all around boards (ceiling, floors, walls, sockets) as per @nod’s way of doing it. 

 

Plasterer said he’s happy to have them all completely flush against walls (no void) but warned of potential issues with skirting having gaps if block work is slightly off in places. Blockwork look immaculate to me so tempted to go this route.

Edited January 3 by Gaf

[nod]

I’d tell to just do his job right Of course there will be voids There has to be at least 12.5 mil to get over the 25 mil back boxes 

 

Id be looking for another dry liner with a bit more experience if he thinks he’s doing a special job by sealing around the boards 

Edited January 3 by nod

[Gaf]

2 hours ago, nod said:

I’d tell to just do his job right Of course there will be voids There has to be at least 12.5 mil to get over the 25 mil back boxes 

 

Id be looking for another dry liner with a bit more experience if he thinks he’s doing a special job by sealing around the boards 

 

Boxes are partially chased. They checked measurements and flush to wall would just work.

 

Out of curiosity, if a parge coat has been added to the block work, then the plasterboard is added using the proper approach (sealed top bottom sides sockets etc), is there any risk of trapping moisture behind the boards?

Edited January 3 by Gaf

[joe90]

2 hours ago, Gaf said:

as per @nod’s way of doing it. 

As per the correct way of doing it 🤷‍♂️

[Gaf]

11 minutes ago, joe90 said:

As per the correct way of doing it 🤷‍♂️

 

I did have that written initially but wanted to acknowledge nod’s advice 👍

[nod]

12 hours ago, Gaf said:

 

I did have that written initially but wanted to acknowledge nod’s advice 👍

You will have a void behind the boards 

We tell kitchen fitters etc measuring prior to plaster To allow 30 on the top of the blocks for D&D

[Gaf]

On 04/01/2025 at 09:46, nod said:

You will have a void behind the boards 

We tell kitchen fitters etc measuring prior to plaster To allow 30 on the top of the blocks for D&D

 

With there being a sealed void, do you do any pre plastering moisture check? 

 

Conscious we have a parge coat on internal leaf, so with this in place, if the plasterboard is properly sealed, is there a risk of trapping moisture?

 

The windows in the house were saturated with condensation, so I’m wondering if there is a possibility that the parge coat could also be retaining water that will be sealed into the voids.

[nod]

5 minutes ago, Gaf said:

 

With there being a sealed void, do you do any pre plastering moisture check? 

 

Conscious we have a parge coat on internal leaf, so with this in place, if the plasterboard is properly sealed, is there a risk of trapping moisture?

 

The windows in the house were saturated with condensation, so I’m wondering if there is a possibility that the parge coat could also be retaining water that will be sealed into the voids.

No

It will be fine 

[Gaf]

12 hours ago, nod said:

No

It will be fine 

Sorry for one more. Would you bother doing this sealing for the plasterboards on the internal walls?

 

I’m getting the plasterboard on the inner leaf of the external walls all done with the full sealing. On the internal walls though, I’ve read it can be useful to allow the inner block walls to heat up - supposedly can act as a bit of a heat store that can release heat back into rooms. Plasterer said he could float some walls but that he can’t guarantee no cracking due to settlement in the house as it’s a new build.

[nod]

6 hours ago, Gaf said:

Sorry for one more. Would you bother doing this sealing for the plasterboards on the internal walls?

 

I’m getting the plasterboard on the inner leaf of the external walls all done with the full sealing. On the internal walls though, I’ve read it can be useful to allow the inner block walls to heat up - supposedly can act as a bit of a heat store that can release heat back into rooms. Plasterer said he could float some walls but that he can’t guarantee no cracking due to settlement in the house as it’s a new build.

Top and bottom on internal 

[Gaf]

1 hour ago, nod said:

Top and bottom on internal 

No sealing on internal wall sockets? 

[Gaf]

The remedy for having used no adhesive around the perimeters or around sockets has been to use expanding foam. See attached. 

 

Holes are 20-30cm apart. No idea what type of foam used.

 

Wondering if foam sprayed into holes 30cm apart will event ‘meet’ to form a continuous perimeter.

 

On a lower wall piece, two holes were ~15cm apart and I could get a cable tie pushed up the wall in between the two holes (behind the plasterboard) suggesting the two pieces of foam were not forming a barrier.

[Redbeard]

Nope. I have always done it 30-50 apart. I would treat 50 as the outside of the 'range of tolerance'. Are they using air-tight foam? (It can be about 2x the £ of 'ordinary foam')

[Gaf]

16 minutes ago, Redbeard said:

Nope. I have always done it 30-50 apart. I would treat 50 as the outside of the 'range of tolerance'. Are they using air-tight foam? (It can be about 2x the £ of 'ordinary foam')

 

For your distances, are you using mm? So max distance should be 3-5cm and not up to 30cm apart?

 

No idea what they used. Not confident of them using the right stuff considering they didn’t just plaster them correctly from the start.

[Redbeard]

Sorry, yes, mm. (I had mentally already converted your cm to mm!). Try a test: drill some 10mm holes in an offcut of plasterboard and mount it the requisite distance from  another offcut of plasterboard. Try 1st with holes @ 300 centres, fill a few and then peel off one sheet of plasterboard. Look and see if the patches of foam touch. Try again at 30-50mm centres. Repeat.

[Gaf]

5 hours ago, Redbeard said:

Sorry, yes, mm. (I had mentally already converted your cm to mm!). Try a test: drill some 10mm holes in an offcut of plasterboard and mount it the requisite distance from  another offcut of plasterboard. Try 1st with holes @ 300 centres, fill a few and then peel off one sheet of plasterboard. Look and see if the patches of foam touch. Try again at 30-50mm centres. Repeat.

Yeah I’m at the point of just doing this job myself. Will be third conversation with builder about this and it’s not getting through. 

 

Are there any generally accepted makes of airtightness foam you’d recommend?

 

One thing the builder I think had right in this was telling plasterer not to use expanding foam so as not to pop the boards off.

[crispy_wafer]

Illbruck fm330 is the go to, Soudal do one aswell.

[Gaf]

27 minutes ago, crispy_wafer said:

Illbruck fm330 is the go to, Soudal do one aswell.

 

Forgive stupid lay person question. While the fm330 is an expanding foam, is it the ‘low post-expansion’ that means it isn’t going to pop the boards off?