Dear all
Can I pick your brains please.
I'd like to add some IWI to my front wall (victorian terrace with a bay window). It's quite a small area and I plan to have max 60mm insulation. So tiny job really.
It's partially to make the walls plumb as I've now had high quality windows installed.
My main issue is that the wall is highly irregular.
The plan is to frame it out so the wall becomes level and plumb and true with the windows. This will create a small cavity which I would like to fill with insulation.
However if I used batts there will be lots of gaps as the wall above the window sticks out about 50mm more than the below the window.
I thought about boarding it out with OSB and then shoving something like Gutex thermofibre in it.
This is the sort of blown insulation that you're supposed to use a special machine for which would be ridiculous in my situation.
What do you think? Do you think using the blown insulation but just pouring it in would work?

Thank you

Yeah, parge coating - is it OK to use insulating lime plaster?
And if walls are pretty straight/plumc, but rubble-stone-rough, the parge only needs to be thick enough to bury the high spots? Which in some areas would be quite thin, like 6-8mm. Or in that case, governed by the minimum thickness that lime render has to be, for easy application?

Posted By: David LamDo you think using the blown insulation but just pouring it in would work?

Generally no. The blown-in stuff is designed to be blown in under pressure to achieve the required and certificated density. There are often equivalent products designed for loose-fill. e.g. we have blown-in Warmcel in our roof, but they also sell a loose-fill product for laying in lofts.

But certainly some blown-in or tipped-in product seems like the way to go for your situation. In our case they blew in to open spaces that they covered with muslin and then we fitted plasterboard over the top.

Ah! Missed this one as my computer 'died' yesterday. It has been resuscitated. The Diathonite/Gutex 'sandwich' looks OK, but a lot depends on whether you want straight walls. Years ago we did a 'country cottage' which had been 'squared up' in the '60s and '70s. When we chopped off the tiles and gypsum in the kitchen we found parts were over 75mm thick, and the underlying wall far from straight or square! We hastily amended our order and instead of 100mm WF over a flat and plumb parge coat we used 40, 40 and 20 and 'wrestled' it over a 'wibbly wobbly' parge coat. Needed more fixings than usual, but it worked well.

Posted By: Nick Parsonswe used 40, 40 and 20 and 'wrestled' it over a 'wibbly wobbly' parge coat. Needed more fixings than usual, but it worked well.

So Nick does 'worked well' mean an aesthetic preference for the original old 'wibbly wobbly' finished walls instead of the dead hand of squared-up modern utilitarianism which also involves significant loss of room interior dimension?

And Beau, I think I've seen your barn, if it's that building, and it's airy and simple enough to look great all straightened up. Excellent idea, those screws - I was not aware of them.

Perhaps I'll start a new thread, but wd love response to my parging Qs a few posts back.

FT said:

''So Nick does 'worked well' mean an aesthetic preference for the original old 'wibbly wobbly' finished walls instead of the dead hand of squared-up modern utilitarianism which also involves significant loss of room interior dimension?''

In some ways I suppose it meant that, as a 'not-a-plasterer' there was no way I was going to (be able to) square that wall up and also that I agreed with the client that a 'rustic' rubble-stone wall did not necessarily want too may straight lines. The 'worked well' mainly referred to the 'wrestling' of the 3 thicknesses of WF board, about which I was by no means certain when I started. Lots of 'fluff-caulking', though.



and

''Perhaps I'll start a new thread, but wd love response to my parging Qs a few posts back.''

Which I guess was:

''Yeah, parge coating - is it OK to use insulating lime plaster?
And if walls are pretty straight/plumc, but rubble-stone-rough, the parge only needs to be thick enough to bury the high spots? Which in some areas would be quite thin, like 6-8mm. Or in that case, governed by the minimum thickness that lime render has to be, for easy application?''

Sorry, missed this one.

Straight answer, I do not know, but since the parge coat is, for me, a 'wet' air-tightness layer I cannot see why an insulating plaster would not work. I always use lime, for breathability, and many (but not all) insulating plasters contain lime. I tend to go for 6-10mm, but there again I am no longer contracting on a regular basis, so it's a bit more theoretical now!

I hope that's of some use.

Cheers,

Nick

I've used the Diathonite cork/lime plaster to spray on as a parge coat (over 600mm stone wall internally, approx 200m2).

Is it OK to use?? I explained to the people at "Ecological" what I was going to do and they had no issues. I can't say for sure if it was air tight, but at about 20mm thick, it certainly gave a homogenous appearance.

I installed a timber stud frame (with frametherm32 wool between studs), so I wasn't too concerned about parge coat appearance... though I got the builder to draw a straight edge over it, to remove ay high spots, in a vaguely plumb manner

I used the insulated render rather than just lime, to capture a bit more insulative build-up. In hindsight, since I added insulation, it might have been more cost effective to use regular lime, and do a bit more with added insulation layer. You gotta try these things sometimes, and not just contemplate.

Hi Paddy, did you say you IWI'd with mineral wool, hard up against an (insulation-plastered) masonry wall which is now cooler than the room? Did you have a VCL?

I've been nervous about wool in contact with cold/cool masonry, due to potential condensation on the masonry surface that soaks into the wool. Many IWI suppliers seem to recommend either: moisture-buffering IWI (woodfibre, cork plaster, etc) that can absorb said condensation and wick it back into the room; or moisture-resistant IWI (foiled&taped polyurethane insulation boards, etc).

How did the mineral wool insulation fare? As you said it is great if it has been tried for real!

@WiA - haven't been back to open the walls to check for moisture at the wall face. There is a vapour check of sorts, ie. foil backed plasterboard, which I never normally use, but I wanted to retard the movement, not seal the walls.

I expect the inch of cork parge, and the lime mortar joints, will control any vapours, with travel in both directions. My feeling is that once it's parged, there won't be any of the fortuitous ventilation, to spirit away the moisture, so I want it to travel back into the house or through the lime mortar in "dryer" months.

We've got some cold weather coming this week I believe, so might call in and ask if I can open a couple of socket back boxes.

Paddy, thanks for that going to that effort and reporting results here, really appreciated.