cavity insulation using cans of PU expanding foam

[swimmydeepo]

In a previous post someone mentioned using cans of expanding foam to insulate a narrow cavity wall (while building the wall). I am rebuiling an external wall and dealing with a narrow cavity about

20-30mm. While there are advantages of having a void space between two leaves of bricks; wouldn't be better to fill such narrow gap with expanding foam? (in a gradual way as the wall is being rebuilt)

Here are the advantages (AFAIK): a) improved stability (as the two leaves of bricks are in direct contact and therefore better loads distribution) b) less cold bridges (no mortar is allowed to fall in the gap) c) warmer house? (a bit of insulation is probably better than none...) d) less noise from outside? (I have some doubts about this)

Point (b) above is particularly important in the long term; as I found out (while taking out the old bricks), that the cavity wasn't void after all, as the old mortar (in form of solid chunks and powdery dirt) was accumulating within the cavity creating many cold bridges particularly at the bottom of the ground floor.

Any comment greatly appreciated

Alex

[The Natural Philosopher]

Its probably better than nothing. Not sure what the U value of expanding foam is. 20-30mm is not a lot really for anything.

[meow2222]

Just one teeny weeny very minor disadvantage: the foam expands after it has solidified with great force, pushing the wall apart and causing it to collapse.

NT

[The Natural Philosopher]

Not it doesn't. As long as it has somewhere to escape to.. In this case the OP was quite clear that every course or 5 would get a squirt (presumably the next day) to fill up to where the bricks had got.

My experience of the cans is that it finds an orifice and bulges through that..in a deep cavity it will simply rise upwards till its done its stuff.

[Broadback]

I would have thought that was quite an expensive option. Many years ago I built a boat with hollow keels in which was place the ballast mixed with resin. When finished, as a hollow would have been undesirable, I had 2 containers of liquid, which when mixed foamed, this was much cheaper than buying the "spray" cans. Sadly because it was long ago (not that age has caused me to lose my marbles you understand) I can neither remember the source nor the name.

[meow2222]

I guess if you did it layer by layer and let it cure between each it probably would be ok, but thats a hell of a slow way to build a wall, or insulate one.

If you do use squirt foam, at last bunging a load of polystyrene foam in with it would reduce costs. Squirty cans arent especially cheap.

Rockwool batts & ss ties would seem a more sensible optoin. I'd have far more trust in ss lasting long term than PU foam.

NT

[Bookworm]

Try the 2260 material at

[Dave Fawthrop]

|In a previous post someone mentioned using cans of expanding foam to |insulate a narrow cavity wall (while building the wall). |I am rebuiling an external wall and dealing with a narrow cavity about |20-30mm. |While there are advantages of having a void space between two leaves of |bricks; wouldn't be better to fill such narrow gap with expanding foam? |(in a gradual way as the wall is being rebuilt) | |Here are the advantages (AFAIK): |a) improved stability (as the two leaves of bricks are in direct |contact and therefore better loads distribution) |b) less cold bridges (no mortar is allowed to fall in the gap) |c) warmer house? (a bit of insulation is probably better than none...) |d) less noise from outside? (I have some doubts about this) | |Point (b) above is particularly important in the long term; as I found |out (while taking out the old bricks), that the cavity wasn't void |after all, as the old mortar (in form of solid chunks and powdery dirt) |was accumulating within the cavity creating many cold bridges |particularly at the bottom of the ground floor.

It may well be worth while buying a large can of polyurethane plus ?foamer?. I once *long* ago mixed my own foam from two parts. You mixed them in a paper cup, and they expanded like mad.

[swimmydeepo]

Well, being a beginner, I'm rather slow anyway...

hmmm, polystyrene isn't PU is it?

Nothing prevents from using ties alongside PU cans...this would certainly improve stability and also counteract the possibility of lateral expansions from excessive use of PU foam.

Thanks for your comments.

Alex

[meow2222]

No. Is there a problem I've missed? More significantly it also reduces expansion forces, since a fair bit of the material, the polystyrene, wont be trying to expand, plus can squish a bit.

It wouldnt at all. Having got caught out once by that stuff I know the forces it exerts are surprisingly high. Mortar is pretty weak for the first day, I think youre really asking for trouble using it, as well as unnecessary expense. But let us know how it goes, good luck!

NT

[Broadback]

They certainly exert a good force, when I did my boat I quickly poured in the mix, covered with thick ply then stood on it, lifted my (12 Stone) no problem! My worry would be that it set on the top before it finished expanding, so went sideways.

[Dave Liquorice]

The domestic stuff certainly continues to expand for quite some time after the initial and comparatively rapid expansion after being squirted. Provided it has space for that I wouldn't expect there to be much force involved.

However not all "squirty foams" are created equal. The stuff used by our recent window fitters did the inital expansion and then stopped. Wasn't paying enough attention to see product details though. Pale blue in colour and the applicator was a proper metal thing that they could reuse repeatedly from the same can.

The latter point might be worth bearing in mind with domestic cans, I've never managed to use the remains even after a couple of hours let alone a day or three, even after cleaning the nozzle and can orfice.

Personally PU foam sounds messy, slow and expensive. SS wall ties and

30mm Kingspan (or similar) would be much cleaner, quicker and quite probably cheaper. Oh and what would the BCO think of PU foam...

[swimmydeepo]

You are right, not all PU foams are the same...a newer type is being sold at Screwfix which expands in a more controlled fashion but it is a bit more expensive.

The applicator you are referring to is probably the spray gun. I've just bought one for less than a tenner as I was fed up of having to throw away half used cans.

[nafuk]

I've notice that solid foam insulation in cavity walls is held in place with rings that prevent is from touching the outer wall. Flexible insulation is however jammed in and touches both walls. This may of may not be relevant.

[meow2222]

I've used it, not as cavity insulation but between ceiling joists, and the forces exerted and the amount of expansion after set gave me quite a surprise. Theres really no way that newly laid brickwork would have survived that. It had 2 or 3 directions in which it could expand as well as down, but down it went anyway, with great force.

I'm sure all foams are not the same, but if youre going to put the work into building a wall you'd need to know which foam is ok to use, and it seems none of us do.

I quite agree about ties and sheet insulation, it makes more sense all round. Leaving a small gap between insulation and outer leaf reduces the small risk of a damp problem.

NT

[Guy King]

The message from "nafuk" contains these words:

There's rules about partial fill/complete fill cavity insulation. It depends on which bit of the country you live in - there are maps with zones on.

[Dave Liquorice]

First time I used domestic squirty foam the amount of secondary expansion caught me by surprise as well. OK the tin did say expands to twice it's volume but twice what? The size of the nozzle or the first rapid expansion? They mean from the first rapid expansion, which is about twice the nozzle...

Quite agreed, and I'm pretty sure the stuff isn't closed cell so will transport damp from one side to the other not good when in contact with both the inner and outer walls. Also there will be the boundaries between the different layers, they'll be open for capillary action...

[meow2222]

hadnt thought of that. It also tends to set in dog-turd patterns, so there will be lots of low angled surfaces for any water to sit on and soak into.

NT

[The Natural Philosopher]

Ah. Thats why they use it to make sure canoes filled with it sink properly.

Glad you cleared that one up..

[Dave Liquorice]

As has already been pointed out there are PU foams and PU foams. The domestic stuff I used ended up very open and with cell sizes from a mm or less to a cm or more! The stuff the window fitters used had much smaller cells approx 1 to 2mm and pretty uniform as well.

I wouldn't trust the domestic variety for a bouyancy application the other stuff I might after a few tests... Didn't think canoes needed any bouyancy now surf boards(*) on the other hand but the foam there is well sealed inside the outer shell.

(*) Cue the URL for the surfboard/foam story...