best 'foam' for sticking Celotex to floor joists?

[Harry Davis]

Hello, what's the best 'foam' for sticking Celotex to floor joists, and can someone advise on how long it takes to bond?

Cheers!

Harry

[Lobster]

I just use no-more-nails type stuff - works very well. David

[geraldthehamster]

Yes, any bog-standard expanding foam will stick it to the joists and fill any gaps. The last time I checked, Toolstation was cheaper than Screwfix. On no account buy from B&Q; their prices for foam are ridiculous.

It's worth getting a foam gun if you're going to fix quantity.

Cheers Richard

[NT]

Do B&Q have sensible prices on anything?

NT

[NT]

Technically the OP asked for the best foam, that'll be the fire rated stuff. Seems an odd thing to ask though, whats the cheapest that performs satisfactorily would seem more sensible.

NT

[Harry Davis]

NT wrote in news: [e-mail]:

I doubt I will be leaving only tiny gaps, and there may be a lot of air movement in the crawlspace, so what I need is

• good adhesiveness to both the Celotex and the joists

• ease of getting it to fill the gap

Expanding foam sounds good.

Are there types that don't expand by a huge amount? I recall using some stuff that expanded to about 29 times its original volume. I didn't have much fun with it, and found it hard to control.

Harry

[NT]

Its fine to cover them if they sit on the PB ceiling, just dont bury them all round in insulation

NT

[fred]

In article , Harry Davis writes

If you use an applicator gun then you can dispense very controlled amounts, the gun has a shutoff at both ends of the tube so when you release the trigger the flow stops straight away meaning you can use it very sparingly.

By using regular foam you will save quite a bit, I did some quantity sums in reply to a previous question[1] which came out at 9 cans for a floor of 8m x 4, so you could end up using 2-3 times as much.

Bear in mind that you will need to hold up the boards with a sideways nail, peg, wedge or similar while the foam sets.

[1]

[geraldthehamster]

Yes, there are. The stuff sold for fixing windows is low-expansion. But you shouldn't have too much trouble with any bog-standard foam, especially if you use an applicator gun.

Cheers Richard

[Grimly Curmudgeon]

True, there is a special drywall fixing low expansion foam, which is about 2x, from what I see. My local hardware shed has several 2for1 offers on the shelf, as it's not a good seller, being about twice the price of the normal yellow stuff.

The normal ones I've been buying recently have been 2, 3, or 4 x expansive, according to the can blurb. They've been gun grade, so perhaps it's more expected to be low expansion in that use. Certainly, the hand cans I was using were hugely, variably expansive a few years ago, to the point where I didn't know how much to apply, as it was nearly always wrong.

[Fred]

Is it ok to have them sitting on the ceiling? All the ones I have ever seen do, but I thought in theory they should be clipped?