Green Building Forum - EWI fixing: mechanical vs adhesive vs mechanical + adhesive Sat, 06 Jun 2026 08:59:07 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 EWI fixing: mechanical vs adhesive vs mechanical + adhesive https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180126#Comment_180126 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180126#Comment_180126 Wed, 17 Jul 2013 21:01:34 +0100 Shevek
As I understand it these are the options for fixing external wall insulation:

1. Mechanical fixings only
2. Adhesive fixing only
3. Adhesive + mechanical fixings

WIth the two adhesive options being:

A. Mineral adhesive, with 50-100% coverage to the back of the board
B. PU foam adhesive, with perimeter and zig-zag coverage to back of board

And in all cases good practice being to fill the gaps between boards with PU foam to optimise thermal performance.

Discussion here on 100% PU foam adhesive:
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9140

And attached is a document from Parex about why the recommend [mineral] adhesive over mechanical fixing.]]> EWI fixing: mechanical vs adhesive vs mechanical + adhesive https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180127#Comment_180127 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180127#Comment_180127 Wed, 17 Jul 2013 21:03:40 +0100 Shevek
Just can't decide between mineral or PU foam. Are the similarly priced?]]> EWI fixing: mechanical vs adhesive vs mechanical + adhesive https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180131#Comment_180131 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180131#Comment_180131 Wed, 17 Jul 2013 21:37:02 +0100 jamesingram Not used PU foam , but have used mech. fixing only , but this was on 'tin tops' post war prefabs.

Cant speak from experience but PU only makes me slightly nervous, if you don't mix/shack up the can correctly or get a dodgy batch, PU foam can go a bit dusty over time (happen when exposed also (UV?)

I like mineral +fixings
When combed up it give a good full bed with room to level up
I'm used to spreading stuff with hawk and trowel
You use the same gear for mess coat
could be consider an external parge/airtightness layer behind insulation
mech. fixing hold it in place whilst working on adjancent boards.
they also pull it in a bit , make it feel more secure.
Can live with small thermal bridge of 2 fixings if it reduces potential for failure rate.

PU foams
nasty , horrible toxic stuff that gets all over your hand and clothes and gives you a headache.

But as said not used it for EWI, so it might be great !]]> EWI fixing: mechanical vs adhesive vs mechanical + adhesive https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180137#Comment_180137 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180137#Comment_180137 Thu, 18 Jul 2013 00:13:33 +0100 Swarm
I also really don't like the thought of a slab of insulation, plus attached brick slips falling from a great height, or having to get scaffolding back to fix it etc. Even if it's a very remote possibility.

Thank you for the PDF too, interesting bed time reading. :)]]> EWI fixing: mechanical vs adhesive vs mechanical + adhesive https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180200#Comment_180200 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180200#Comment_180200 Thu, 18 Jul 2013 21:45:50 +0100 TimSmall
With either adhesive, I don't think you'll get either insulation off without destroying the blocks.

Don't know about GWP of either system, but I know that the PU is quicker (and I believe a bit easier, BICBW I've never used the mineral stuff).

I believe that you're supposed to use mechanical fixings along with the adhesive above a certain height with EPS above a certain height (two storeys?) - due to risk of the render layer heading downwards in a fire I think.

Also a requirement to put in a rockwool firebreak between the 2nd and 3rd storeys in my case I think when I looked into it (according to the Weber BBA cert I think). Not done the EWI except on the loft conversion yet, so I'm not 100% sure.

Tim.]]> EWI fixing: mechanical vs adhesive vs mechanical + adhesive https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180203#Comment_180203 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180203#Comment_180203 Thu, 18 Jul 2013 22:42:42 +0100 Shevek Posted By: TimSmallAlso a requirement to put in a rockwool firebreak between the 2nd and 3rd storeys in my case I think when I looked into it (according to the Weber BBA cert I think).
Oh, that's a point. We're mid-terrace. Do we need those vertically at the party walls?]]> EWI fixing: mechanical vs adhesive vs mechanical + adhesive https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180211#Comment_180211 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10902&Focus=180211#Comment_180211 Fri, 19 Jul 2013 07:30:47 +0100 jamesingram Posted By: Shevek
Posted By: TimSmallAlso a requirement to put in a rockwool firebreak between the 2nd and 3rd storeys in my case I think when I looked into it (according to the Weber BBA cert I think).

Oh, that's a point. We're mid-terrace. Do we need those vertically at the party walls?
I'd have thought only if your neighbour EWI or have flammable cladding etc.
One thought RE PU foam , it's a lot less to ship about so EE (embodied energy) might be much less ??]]>