Gaf

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?

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.

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.

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.

Just returning to this as time to decide now coming up. Have kept the above in mind and angling towards 8kW Thermia iTec Eco with 300L DHW tank. Tank would not be the Thermia one and instead another branded one since max Thermia one is 240L. We’ll have two adults and two kids (so four adults down the line) so will need a good tank for all the showers.

Perfect, so it’s all about prevention 👍

We plan to get the water treated, however a neighbour with a well likely running off the same water table has had two DHW tanks go kaput in the past 10 years. Supposedly no particular issue can be identified as to the cause of the two going kaput. Both were under warranty so replaced without issue but we still want to consider what our DHW might need to be. We're in a hard water area (you'd want to see the limescale on another neighbours kettle 🤣). Neighbour said theirs was 'marine grade', but searching here I've seen this is a bit of a marketing term. It seems it's about the grade of steel that is the most important aspect? DHW will be connected to A2W heat pump and my understanding is it will be unvented. No solar. I've seen Joule and Dejong mentioned, not sure if these are well regarded makes?

No sealing on internal wall sockets?

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.

Yes a 150mm cavity wall (bead insulation) and the IWI was needed for BR. When you say the floor will “bridge” the IWI, do you mean if the IWI runs up along the wall into the service void to meet the underside of the precast floor? As in, the IWI ‘touching’ the underside of the precast will effectively insulate the whole void? That was my understanding of why the IWI runs up into the void. The builder and plaster (and builder’s architect, not my own) say they’ve never seen this done and have never done it, so they didn’t follow the plans and have not installed the IWI into the wall at the service void.

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.

That was my thinking. Builder and plasterer said they’ve never seen this ever. Builder said he touched base with his architect on it and he said they never do this, is unnecessary. It has been parge coated. No the drawing in that area is actually strangely inaccurate. The concrete slabs are sitting on the full block.

Is it typical, or recommended, that ground floor IWI continues up the into the service void to meet first floor precast concrete floor from beneath? *Aware I'm posting a bit lately. Each post is related to a different specific query. Apologies if I should be merging the posts.

Yeah the various opinions on building is difficult to disentangle for a novice doing their first (and bloody last) build 🫣😃

There were gaps as it turns out. They’ll be sealed and retested. Plan to be there for the retest. In Ireland. Pics attached to last two posts. No log burner. There were holes in overall airtightness approach and one wall hadn’t been parge coated (all being rectified).

Got dark on me quicker than expected so didn’t get a wall to ceiling or wall to floor junction image on ground floor. We have precast concrete first floors. These are hollow core but they are pumped with what looks like a string polystyrene-like filling for airtightness. There was also an airtightness membrane wrapped around the concrete floors where they rest on the external walls (resting on inner leaf), this membrane wrapped from ground floor ceiling junction to first floor floor junction. All external walls (inner leaf) are parge coated. It doesn’t look like any particular attention went to floor junctions on either floor, and no attention to ceiling junctions on ground floor. The reveals in the images don’t have the parge coat, but this is being done. The air tightnes tester will be coming back. When the test was done, there: - A ~30cm hole torn in the airtightness layer above the stairs. Was done for a pulley/winch to lift plasterboard to first floor. This is being resealed. - One wall (1.2m x 4m) hadn’t been parge coated. This is being done. - None of the electrical conduits running into the cold attic were sealed. These will be sealed now.

Four attached as max file size upload reached.

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

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?

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.

Figured it out. Architect plans didn’t include a depth for battens or dot-dab. Waiting on a reply from on why. At present I can only surmise they intended the IWI to be affixed directly onto blockwork.

Currently the dabs are adding 25mm. The PIR on the boards is 25mm for reference (attached image). Blockwork was snooker table flat. Looking along an >18m long wall, there wasn’t one block out of line. Block work was excellent. There is a parge coat. Yeah I’m posting a bit at the minute to make sure Im on top of what’s being done in site now. 😬

Aware this is probably not the ideal way of doing it, but if you had to, what’s the best way of affixing IWI directly to block work? As in no void behind the boards. Reason is a potential issue with architect forgetting to allow for battens/dot-dab thickness in room calculations. House went up based on external wall measurements so now internal walls are all 2.5cm thinner with dot-dab method (5cm across walls). Not end of the world, but want to know what option there is with direct affixing to blocks. I’ve seen a screw in method but also read this risks breaching airtightness if not done correctly.

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)?

Only to meet building regulations, so under 3. Our architect did not spend much of any time considering an airtightness strategy (general notes in spec about various areas being made “airtight”) and I did not know enough about it at that stage of the process to ensure it was focused on. I can see why so many knowledgeable folk here attend to these things themselves. Im accepting that i can only hold the builder to the regs. My understanding is that the airtightness work should get the house < 3, and not the plaster work.