Using expanding foam questions

[Sparrowhawk]

I'm foaming PIR in place as a cavity closer with airtightness as the goal, where one wall is fairly straight and the other isn't. I've got Illbruck FM330 on the gun at present.

 

1. How small a gap can I foam? On the straight side I cut it fairly snug and cut V shaped notches to put the foam gun in. I thought the foam would squirt in then move vertically to fill the gap. It did that for a cm or two and then came straight back out of the notch

 

 

2. Is there a way to get expanding into small spaces?

On the non-stright side, between some bricks there's angled gaps and the foam has stopped expanding before they're filled and airtight - preferring to expand along the wall rather than into it. I know that FM330 is low expansion foam so is this

a) the wrong foam to use here

b) something expanding foam won't do

c) user error

[crispy_wafer]

I use these nozzles, good for tight spots.

 

https://www.ebay.co.uk/itm/256270021355?_nkw=expanding+foam+gun+nozzles&itmmeta=01J5JV75ZS7DY2NK1HP7VC2AZM&hash=item3baae232eb:g:ULgAAOSwcyNlMD77&itmprp=enc%3AAQAJAAAA8HoV3kP08IDx%2BKZ9MfhVJKk%2Brqx7%2Bbsuyp7ejiKYKTnebIP9W39Ke6NzjORcTdOnidiG%2FO2v%2FljpnR2lybJ7icSHncP3PxeeJdQ1ppIb6Q79DTtVzxTLDT4xOLNcesZRyjj3KhpHn40hGTfyZKF1CBUBWbXUL%2BtkWFMhmEEBEVJBlNoGU0rH0wVXonGlzWhN22qmWnQDF1QHT4yGLbNshL%2B666a5jRYv%2B7FKi9cZPbpKh6HIzTyb%2FpQrgivfnzh0I95r83q0tTOCoJ3g6f9tSXIPMufGl7oBkGp0nVYf%2B27%2FTVxbMQd08y171g1GIuFt7Q%3D%3D|tkp%3ABFBM-t-c26xk

[crispy_wafer]

Belt and braces, I’d tape it too, or event give it a good couple of coats of soudatight paint.

[Sparrowhawk]

On 18/08/2024 at 14:37, crispy_wafer said:

I use these nozzles, good for tight spots.

 

Thanks those look useful to have. I also found spraying the smaller cracks with water is helping the foam expand and fill them.

[joe90]

3 hours ago, Sparrowhawk said:

I also found spraying the smaller cracks with water is helping

Yes damp surroundings always helps.

Edited August 25 by joe90

[SteamyTea]

12 hours ago, joe90 said:

Yes damp surroundings always helps.

Also makes it shrink back more, so as with most things, not as simple as first seems.

[Andehh]

For that level of extreme air tightness, do what you can with expanding foam then go over it again with silicone and fill the holes that way!

[Oz07]

Can you cut the boards like 15 or 20mm short of the cavity width. Couple of bits of duct tape to hold in place with even gap ea side then just run the foam gun down both sides? I always prefer a bigger gap to foam, smaller gaps always struggle. When cutting pir between joists on floor refurb i did this and just banged some nails half in sides of joists pushed board down onto these. Admittedly I was trying to stop wind washing not get airtight. Might not work in this scenario just a thought

[Dave Jones]

allways easier to use cavity closers built in ass you go. Tape the closer to the inside skin using the proper cloth airtightness tape.

[Sparrowhawk]

2 hours ago, SteamyTea said:

Also makes it shrink back more, so as with most things, not as simple as first seems.

 

Good to know, and nothing ever is. It seems too much water also overexpands the foam leading to a weak mess with large bubbles.

 

55 minutes ago, Oz07 said:

Can you cut the boards like 15 or 20mm short of the cavity width. Couple of bits of duct tape to hold in place with even gap ea side then just run the foam gun down both sides? I always prefer a bigger gap to foam, smaller gaps always struggle. When cutting pir between joists on floor refurb i did this and just banged some nails half in sides of joists pushed board down onto these. Admittedly I was trying to stop wind washing not get airtight. Might not work in this scenario just a thought

 

I've tried this with the next bit and it's worked better with more foam than my first go. Problem was I was overthinking, as a small bead of foam gives less insulation at the edges than 5cm of PIR so was trying to minimise that amount that was just a dab of expanding foam. But getting it done and airtight ftw.

 

12 minutes ago, Dave Jones said:

allways easier to use cavity closers built in ass you go. Tape the closer to the inside skin using the proper cloth airtightness tape.

 

I'll ask my local medium to communicate that to the builder 😁