DIY retro cavity insulation

Half of my house is solid stone. The other half is a cavity-walled extension, built in 1991. When the builder added the extension, he inserted sheets of 1"-thick foam polystyrene into the cavities, as insulation. I would have been better off if he had used *no* insulation! The 1" of polystyrene does little to prevent a cold draft from circulating within the cavity, and it makes it harder to get additional insulation added. Although I am eligible for a grant, the cavity insulating companies say the 1" sheets already installed prevent them from adding extra insulation under the grant scheme. I might be able to pay for it myself, but I'm told that I would have difficulty finding a company who would guarantee the job. If the work is not guaranteed, it means there is also no guarantee that they would make a reasonable effort to do the job properly.
So I have two options, as far as I can see: 1) do it myself (following the "if you want a job done right, DIY!" axiom). or: 2) find a company who I can trust enough to do the job well, but without any guarantee (not easy)!
Can anyone offer any advice on this?
If I do it myself, what materials should I use? beads, fibre or foam? My guess is that foam injection would be the way to go (even though this method seems to be rarely used these ddays for some reason. Anyone agree?
Does anyone have any idea how much it should cost to do it?
Many thanks,
Al
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AL_n wrote:

lateral thought.
Fill the cavity with acetone, or cellulose thinners which will utterly destroy the polystyrene. Then call the cavity wall insulation johhnies back...:-)
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Yes, if only there was a removal process as easy as that...
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AL_n wrote:

it IS that easy..
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On Wed, 24 Aug 2011 11:29:44 +0100, The Natural Philosopher wrote:

But the fumes have got to go somewhere. Presumably half will diffuse through the outer wall and half through the inner wall. That means that over the time when the walls are "drying out" you'll have the fumes from a few gallons of acetone seeping into the house. Be prepared for some involuntary glue-sniffing.
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root wrote:

well I assume a bit of core drilling to the wall first would be useful.
Top get it in..
acetone is fearfully evaporative.
wouldnt last long, but I'd turn off all power and gas first :-)
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Polystyrene bead is fairly easy to diy. You need to rig up a blower, its hopeless trying to pour it in. If you drill the holes on the inside, they can completely disappear afterwards. So take photos as evidence its been done.
NT
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The polystyrene boards will be fixed and there are wall ties to consider, so it is not a simple matter of cutting a diamond of bricks out and ripping the stuff out with cable pullers and custom tools on the end (not unless this is a single wall of relatively small area). If you do take bricks out, tap a it of slate in to tighten things up as it goes off - avoids cracks propagating although I believe there are no-shrink/expansive mortars out there to avoid that.
I suppose polybead would be the best thing - you are supposed to match the existing insulation type. The 1" polystyrene is adequately fixed tight against the inner leaf you would just top up with polybead.
Foam would need to be low expansion, because otherwise you really can push a wall out - wall ties not withstanding. The stuff can cure at the perimeter and continue to exert pressure. Only takes a few psi to push a leaf out.
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I'm wondering why the OP thinks the existing insulation is an issue. It might disqualify for a grant, but it certainly shouldnt be a problem if retrofitting poly bead, which will do a 1" cavity no problem. In fact it'll reduce the cost and improve the reuslting insulation.
http://www.acpackaging.co.uk / but I'm fairly sure I found a cheaper supplier
Do be thorough about blocking any gaps in the wall beforehand :) Escaping masses of beads are the main issue with poly bead.
NT
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That's what I would have thought. However, I know that nowadays, they spray the beads with something that causes them to stick together somewhat (stops everything from spilling out as soon as someone cuts a hole in a wall for any reason). ..And I do plan to cut some holes in the walls at some future date when I install extra windows.
I imagine (perhaps wrongly) that the sprayed beads don't flow as readily into narrow gaps as unsprayed beads. That's partly why I got interested in the injected foam option. Injected foam also has the advantage of not settling and not getting blown around by draughts. I've also read that poly beads allow moisture to cross the cavity, as the air spaces between the beads absorb moisture.
Someone today told me (possibly mistakenly) that DIY foam injection is feasable using equipment from a tool-hire company. They may have been thinking of silicone damp course injection gear.

Thank you for your suggestions...
Al
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I dont think poly beads are generally used for cwi nowadays, the escaping bead phenomenon irked people. When they were, glue coating them was done in theory, but frequently omitted in practice. Beads work fine with no glue, but you need to either inject a tiny bit of foam when you cut/drill the wall later, or just re-fill the area once the work's done.
Escaping beads are messy - easy to clean up but they get everwyere.

One of the plus points of beads is they flow into and fill everywhere, including above the height of the injection hole. Beads dont blow about in the cavity because its filled jam packed full. And the bead form is the best for avoidance of damp issues, it gives you maximum evaporation surface area.

I've no experience with foam cwi injection.
NT

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The white insulation boards that were inserted during teh construction, are not fixed. they wobble freely within the cavity. I have witnessed it myself when cutting 6" holes in the wall for soil outlet pipes. I also noticed cold air blowing around within the cavity, making me feel that the foam sheets are not doing much good at all.
Provided that the modern foam they use for cavity injuection won't melt the existing sheets of polystsyrene, it seems to me that it might be a good option because the expansion of the foam would force the 1" sheets back against the inner skin of blockwork.

Thanks for the warning - I could do without that kind of disaster!
Al
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I wonder if it will melt the existing polystyrene sheets...
Al
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Would a simple solution be to sleeve the air brick and other air transit routes? Draughts require an inlet and an outlet for the current of air.
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Thanks for the suggestion, but I believe the draughts are coming promarily down from the loft. I felt the draft coming out of the cavity when I recently cut a big hole in the wall,to install a new window. I suppose that now the window is installed, there will be less draught in the cavity, but I'd still be a lot happier of I knew the top of the cavity was airtight, full of expanding foam or other insulation. As it stands, all the warmed air within the cavity can rise up into the loft and mingled with cold air from the loft. Not good...
Al
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Surely there needs to be *some* air circulation to reduce/prevent stagnation and mound etc within the cavity, albeit a small amount.
Perhaps filing the top of the cavity only with expanding foam will reduce the air flow within the inner and outer skins and filling below that with beads provide better insulation bt still maintain a small air flow (Probably very tiny)

Thanks for the suggestion, but I believe the draughts are coming promarily down from the loft. I felt the draft coming out of the cavity when I recently cut a big hole in the wall,to install a new window. I suppose that now the window is installed, there will be less draught in the cavity, but I'd still be a lot happier of I knew the top of the cavity was airtight, full of expanding foam or other insulation. As it stands, all the warmed air within the cavity can rise up into the loft and mingled with cold air from the loft. Not good...
Al
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