Garden retaining wall, concrete block k-rend and cavity?

12 Apr 2012
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United Kingdom
Hi folks, I’ve done quite a bit of research but can’t find the exact answer to the exact question I have; do I need a cavity in a 2 skin concrete block wall to satisfy k-rend requirements?

Background. I have had a 1.5m block retaining wall built and hope to k rend it (eventually after other building work complete). I need to build the inner skin next, and was wondering if I should fill the cavity with a strong sharp based mix and PVA, or leave it air gapped so as to have a dry facade? The back skin is block on edge with deadman blocks, good drainage at foundation level into a land drain, back filled top to bottom with 10&20mm limestone and has a couple of large concrete stantions. There is no damp proof or visqueen etc between the limestone and the block.

I’m confident the cavity would remain dry but I was thinking that filling it for a wedge of extra strength might not be a bad thing. I can’t find anything that specifically says a cavity is required for k-rend so what are people’s thoughts here? I guess another question is would a solid wall be more prone to cracking? (but as the fill would be PVA’d, would this help or hinder?)

Many thanks in advance, Phil.
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No - to a cavity.

Rendering a retaining wall will come with (contaminant) risks. You would mitigate ingress by laying a DPM barrier/Geotex fabric against the wall before back-filing. I'm not a massive fan of rendered garden walls (UK) but if need must and all that.
Hi, thanks for the comment. Backfill is complete now behind the back block wall, do you mean membrane behind the outer skin? If so then this would get punctured by the wall ties?
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Critique away! :mrgreen:


Sure maybe the render at the base will get a little splashed from the ground but it won't get blown off the blockwork which is the main issue. The bottom edge of the render may be a vulnerable to spades clonking it or mowers bashing it depending on the location but some care just needs to be taken in its vicinity. The blockwork visible beneath the the render could be painted periodically with little effort or perhaps a strip of PVC screwed or bonded to the blockwork to hide it.
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