Green Building Forum - Gap Fill: Sand, Gravel, lime mortar or something else? Mon, 25 May 2026 12:07:43 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Gap Fill: Sand, Gravel, lime mortar or something else? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1626&Focus=19236#Comment_19236 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1626&Focus=19236#Comment_19236 Thu, 24 Apr 2008 09:20:09 +0100 Roger
I would like some advice. I've laid 100mm concrete over dpm/Kingspan on half-basement barn conversion. The internal wall is quite rustic, rough sandstone, lime mortared, and corbels out slightly at the bottom. I ran a perimeter upstand of 40mm eps around the edge to create a bit of insulation from the cold external wall, and to keep the concrete from the lime mortar/sandstone. This now contains the concrete and will imminently contain the UFH and screed. Any suggestions for filling the up-to-100mm gap left at the back? The wall will inevitably have some moisture in it due to external levels and I wanted something that would let it breath/drain, while filling the void.

Sand? Pea gravel? Polystyrene beads? Damp mix of lime/sand? Any suggestions much appreciated.

Roger]]> Gap Fill: Sand, Gravel, lime mortar or something else? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1626&Focus=19244#Comment_19244 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1626&Focus=19244#Comment_19244 Thu, 24 Apr 2008 11:20:39 +0100 biffvernon
(Shame about the concrete, but what's done is done.)]]> Gap Fill: Sand, Gravel, lime mortar or something else? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1626&Focus=19247#Comment_19247 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1626&Focus=19247#Comment_19247 Thu, 24 Apr 2008 11:53:58 +0100 Roger
I know, limecrete or somesuch preferable but subfloor moist so DPM down and limited budget, hence concrete.

Is there merit though in anything with good thermal properties to fill the gap? The void is between the external walls and the DPM, which laps up behind the EPS. (All to be topped off with flags pointed in lime mortar).

Are those clay granules robust or will they turn to mush if moisteure gets in? Maybe gravel's the best bet.]]> Gap Fill: Sand, Gravel, lime mortar or something else? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1626&Focus=19276#Comment_19276 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1626&Focus=19276#Comment_19276 Thu, 24 Apr 2008 19:40:09 +0100 tony