Fri, 14 Aug 2026 23:00:31 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12071#Comment_12071 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12071#Comment_12071 Tue, 08 Jan 2008 09:05:37 +0000 Pingy
My thinking is that although the new block wall will be wet plastered and therefore hopefully airtight, the cavity in which the insulation will be located may not be so airtight (using mineral wool batts for insulation). Would re-pointing the external lime mortared wall be just as good at making the cavity airtight?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12073#Comment_12073 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12073#Comment_12073 Tue, 08 Jan 2008 09:19:54 +0000 tony
Do not re-point with cement use lime.

I would say not worth doing a parge coat inside the cavity.

How big will your cavity be? and what blocks?

100 or 150 even 300 cavity for me and solid blocks never lightweight.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12074#Comment_12074 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12074#Comment_12074 Tue, 08 Jan 2008 10:18:48 +0000 Pingy
In answer to your questions (plus some more questions):

I'm assuming a wet plastered block wall on the inside would be airtight - am I correct? Wouldn't the parge coat help to reduce air movement within the cavity and improve the effectiveness of the insulation? Should I be installing a separate air tightness barrier?

The building will be re-pointed with lime mortar to maintain it's beathability.

Cavity will be 250mm with full fill mineral wool cavity batts. I'm unsure at the moment what blocks to use. I'd like to use unfired bricks but would have to have something stronger in one area to support a 'mezzanine' floor - your thoughts on this would be appreciated.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12077#Comment_12077 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12077#Comment_12077 Tue, 08 Jan 2008 11:42:33 +0000 tony
In all cases there needs to be an air tightness barrier sometimes it is a separate item, wood, polythene, breather membrane; sometimes it is the wet plaster or the decorations. More often it is not there at all.

Great cavity!! -- love it -- Unfired bricks will be OK and the mezzanine could be built on posts against the walls?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12081#Comment_12081 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12081#Comment_12081 Tue, 08 Jan 2008 12:25:33 +0000 Pingy
I know I'm deviating from the subject slightly but can you advise as to whether it would be possible to use lime mortar for some small single storey extensions to the building. The new extensions will be 4" brick outer skin/250mm cavity/4" block (solid) inner skin. I've read articles about lime mortar having insufficient strength for single brick walls.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12084#Comment_12084 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12084#Comment_12084 Tue, 08 Jan 2008 12:58:43 +0000 tony
Sounds like rubbish to me and your walls are not single skin unless you omit the wall ties

I would use nylon wall ties rather than metal wall ties and separate lintels inside and out.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12085#Comment_12085 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12085#Comment_12085 Tue, 08 Jan 2008 13:21:52 +0000 Pingy
I've also read somewhere that wide cavities do not behave as a single wall, even with the wall ties. They have to be regarded as two separate walls. Sadly I can't remember where I read this either - this is definitely a problem when using the internet to do your research. So much information you can't print everything out so you're left with just the ageing brain cells to record it!]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12098#Comment_12098 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12098#Comment_12098 Tue, 08 Jan 2008 18:15:33 +0000 Mike George https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12103#Comment_12103 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12103#Comment_12103 Tue, 08 Jan 2008 18:48:15 +0000 Chris Wardle https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12104#Comment_12104 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12104#Comment_12104 Tue, 08 Jan 2008 18:59:26 +0000 Mike George http://www.lafargecement.co.uk/home_frame/main_content/frameset_pdf_popup.asp?pdf=../../pdfs/bag/blue_circle_hydralime_bag.pdf]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12122#Comment_12122 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1068&Focus=12122#Comment_12122 Wed, 09 Jan 2008 00:12:17 +0000 TomW Tom]]>