Green Building Forum - Pargeing for airtightness Tue, 19 Dec 2023 08:37:06 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Pargeing for airtightness http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300579#Comment_300579 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300579#Comment_300579 Fri, 03 Mar 2023 10:55:23 +0000 fostertom http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17757&page=1#Comment_300578, am continuing a pargeing discussion here.

Seeking advice on using insulating lime plaster as airtight pargeing on old masonry before IWI.

What I'll be needing it for, is where well-built (flat/plumb but rough surface) rubble Edwardian stonework is lined with lime plaster on lathing on battens, with original skirtings and plaster cornice, to remain, which define the depth of IWI to replace the battened plaster. So prob 50mm IWI incl plasterboard. The Victorians/Edwardians imagined this would provide some insulation, but in fact does worse than the hard plaster that's used instead at 1stFl. This is because the hard plaster at least makes the wall airtight, while the unplastered rubble at GrdFl is highly wind-permeable (and equally permeable to chimney-effect-driven infiltration even when not windy). So at 1stFl the rubble's modest insulation value can have effect, as outside air is impeded from whistling right thro it, but at GrdFl it's unmitigated outside air right behind the lath-and-plaster - same as the plasterboard-tent effect of modern dot n dab in estate houses.

The IWI we will prob pay for Aerogel behind plasterboard, on the parge coat. The thinner the parge can be, the better, and if a little bit insulating itself, also better. My questions are:

1) can insulating lime plaster, with its insulating inclusions, in fact be airtight? At what thickness, for airtightness?

2) separate concern - what thickness must a) ordinary lime plaster, b) insulating lime plaster, be for ease of application, not becoming an expensive faff if too thin?

3) on flat, plumb but rough-surface rubble, obviously plenty of thickness where filling the dips, but a bare skim over the high spots? Will that work?]]> Pargeing for airtightness http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300580#Comment_300580 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300580#Comment_300580 Fri, 03 Mar 2023 11:46:31 +0000 djh Posted By: fostertom1) can insulating lime plaster, with its insulating inclusions, in fact be airtight? At what thickness, for airtightness?A quick search doesn't reveal any information on this subject to me, so I suspect it is a question you would have to ask directly of the manufacturer. Have they undertaken any airtightness testing, especially an independent third-party test? It might also be worth asking standardisation organizations such as the NBS, PHI, BBA etc etc as to whether they have any standards or tests that apply.

2) separate concern - what thickness must a) ordinary lime plaster, b) insulating lime plaster, be for ease of application, not becoming an expensive faff if too thin?
I suspect you'd need to ask a good, experienced lime plasterer.

And the answer to your question 3 obviously depends on the actual thickness of 'bare skim', together with the stability of the wall and the exact mix of the plaster being used. Again, a question for a good, experienced plasterer with some satisfied long-term customer references.]]> Pargeing for airtightness http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300581#Comment_300581 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300581#Comment_300581 Fri, 03 Mar 2023 11:50:06 +0000 fostertom Pargeing for airtightness http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300591#Comment_300591 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300591#Comment_300591 Sat, 04 Mar 2023 12:49:21 +0000 bogal2 Pargeing for airtightness http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300593#Comment_300593 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300593#Comment_300593 Sat, 04 Mar 2023 17:16:47 +0000 cc64 https://www.lincolnshirelime.co.uk/insulation-systems-46-w.asp which I though looked interesting & might be for your application: their LimeCO2te WarmCO2te product " is made with lightweight mineral as the aggregate in place of sand and my results so far put the Lambda value at around 0.125 W/mK, that is about 5 x more thermally efficient than a standard lime plaster and 8 x better than sand and cement. "]]> Pargeing for airtightness http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300599#Comment_300599 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300599#Comment_300599 Sat, 04 Mar 2023 20:20:38 +0000 djh Pargeing for airtightness http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300619#Comment_300619 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300619#Comment_300619 Mon, 06 Mar 2023 12:02:57 +0000 lngn2
None of this seems to be addressed in any of the IWI details one finds online?]]> Pargeing for airtightness http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300622#Comment_300622 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17765&Focus=300622#Comment_300622 Mon, 06 Mar 2023 15:04:26 +0000 djh