Best adhesive for insulated slabs

DublinDilbert · 21-12-2023 12:45pm #1

Hi All,

I was wondering what the best adhesive is for to hold 62.5mm insulated slabs to the wall. I will be using mechanical mushroom fixings, but would like a good bond too, with no air gap, should minimise the amount of mushroom fixings.

I will be using the low expansion foam around the window reveals to bond on the reveal board. But I don't really want an air gap between the slabs the wall. I know not everything will bond to the silver foil.

Its only 3 boards in one room and 2 in another. I was considering using the premixed tile adhesive as that stuff will stick to anything and applying with a notched trowel to the wall and board. Also existing wall is painted, so was going to run the sander over it and probably key the wall too, should enable a better grip.

Thanks.

10-10-20 · 21-12-2023 1:58pm

Hi! I've used most of the insulated plasterboard expanding foam adhesives available in the various builder's suppliers. All appear to be the same product with just different labels.

One thing that I found useful was to invest in a dispensing gun as you can keep the bead a lot more controlled and you get a better distribution of the foam. Also don't fully seal in the area by creating closed squares/rectangles, that causes an air trap and it resists being pushed against the wall. Secure the slabs soon after and don't overdo the amount of adhesive either, there is some force involved over the curing duration and you don't want any it expanding and bowing the board.

Good luck.

DublinDilbert · 21-12-2023 2:07pm

I have used the foam in the past before too, but mainly for door/window reveals where the wall wasn't even anyway. Do you know on a flat wall how much of a gap there would be behind the board?

I'm sure if i get a couple of mushrooms in quickly in the centre of the board it will pull it home. I can also put some long plaster board screws into the wall plate at the top of the wall.

10-10-20 · 21-12-2023 2:46pm

Around 5 to 8mm where the board was checked and secured. One or two went astray after I let them be (without mushrooms) and I ended up with around 12mm in some cases. 😂

I was using it on both reveals and also with full sized 2.4m boards. Great initial adhesion and you can reposition the board for a few mins.

Shoog · 21-12-2023 2:58pm

There is special adhesive foam for this. It's a slightly different formula which doesn't expand as agressively. You apply it and wait five mins before pushing the board to. You push it home and then drill and hammer your mushrooms. The mushrooms will ensure it doesn't deform the board.

IT collapses to virtually nothing on pushing the board home and then carrys on expanding very slightly to fil the imperfections.

Don't be tempted to use the gap filling foam. It's also a good idea to prewet the wall to ensure best activation and adhesion.

The only issue I had was where I forgot to mushroom the corner of one board and it pushed out a bit - nothing a little extra plaster couldn't deal with.

Don't forget to airtight tape over the heads of your mushrooms or they will be a clear path to air and will attract condensation. It's a very good idea to airtight tape all seams.

TimHorton · 21-12-2023 6:06pm

https://www.boards.ie/discussion/2058327878/best-adhesive-for-insulated-slabs

https://www.screwfix.ie/p/dow-insta-stik-expanding-foam-grab-adhesive-gun-grade-750ml/72793

DublinDilbert · 22-12-2023 1:49pm

Hi All,

I've used the low expansion foam for sticking boards before, it is great stuff where the wall is uneven, i was just wondering was there anything that would allow me get the board right to the wall.

I'm trying to minimise the mushroom fixings to limit cold bridging. I will be putting them in strategic locations, behind where the curtain rail brackets will go, behind radiator brackets, at board joints etc... I normally run some screws along the top of each board into the wall plate.

Thanks

10-10-20 · 22-12-2023 2:14pm

https://www.boards.ie/discussion/comment/121526143#Comment_121526143

No, you'd be looking at a contact adhesive and that's not used here. Usually there is a bit of variation in the background anyway, so having 5mm as a buffer is needed to ride-out the dips. I've seen some of mine be almost tight to the wall, maybe 2mm of foam.

Anyway it's not going to become a true cavity and start convecting heat as you'll have the foam distributed across the slab.

GreeBo · 30-12-2023 11:28pm

If the wall you are fixing to is "flat" then cant you just use any sort of adhesive tube? Tec7 etc?

Nylon mushrooms will largely avoid the thermal bridging from the metal ones, so you can use as many as you want.

DublinDilbert · 31-12-2023 11:47am

Yea the wall was flat, so that's what I was thinking. I could use TEK7, but was considering the premixed tile adhesive with a notched trowel. The stuff is cheap and sticks to plaster/foil etc..

GreeBo · 31-12-2023 3:26pm

https://www.boards.ie/discussion/comment/121553203#Comment_121553203

The premix would work, but really its just there to stop air flow behind the boards, the mechanical fixings are whats doing the work. I think I would put a bead of either around the outside and then just use the nylon mushrooms and be done with it tbh. Or just use the mushrooms and tape all your joints and move on :)

Best adhesive for insulated slabs

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