A domestic insulation project chapter 3 – weeks of weetabix walls

Ok, so it wasn’t really weetabix. But it does look similar… The previous phase was dusty. See here. This phase has also been dusty, although not quite to the same extent. But it has also been an exciting stage when most of the taking apart was finished and the reconstruction happened.

The bulk of the walls are being insulated with miscanthus-lime. At some point I will write a whole post about what this is and why I am using it. But for now, some photos and captions…

Installation was by Steve Cole of Addasu. The approach is that developed by Neighbourhood Construction, and a video of the complete process is available here.

Step 1: measure out your ingredients; miscanthus (seen here), lime and water. Photo credit: Billy Aiken.
Until they’d got the hang of how much variability there was in the density of the material in each bag, miscanthus was weighed to keep mixes as consistent as possible. Photo credit: Billy Aiken.
Step 2: measure out your lime (we used Tradical Thermo, which is essentially NHL3.5 with some cement in). Lime is REALLY unpleasant, so Steve is wearing a decent quality ventilated dust mask. Photo credit: Billy Aiken.
A decent quality mask is important when working with lime. Safety glasses are a good idea, particularly if it’s windy, but we had tubes of sterile saline on standby because the most likely way of getting lime in your eye is by absent mindedly wiping your face with your hand. Photo credit: Billy Aiken.
Step 3: materials into the bin mixer. Photo credit: Billy Aiken.
Step 4: Mix! The aim is to tumble/mix the materials gently so that the plant material has a good even coating of the lime and a wheelie bin with a central axle is ideal for the purpose. Conventional cement mixers are NOT good for mixing lightweight bioaggregate insulations; they tend to make the mixture clump together into balls, presumably because they apply a lot more force than when using a tumbling mixer like this. At some point, I intend to write about non-Newtonian fluids and how it is that plasterers intuitively know a lot about rheology without them ever having learnt any big words for it. Photo credit: Billy Aiken.
Step 5: measured volume of water added to the mixer, lid replaced and the mixture tumbled some more. Photo credit: Billy Aiken.
Miscanthus-lime mix ready to use. Photo credit: Billy Aiken.
Pegs are driven into the wall, levelled to the desired insulation thickness, and guide rails attached. The wall is sprayed down liberally to improve the bond between the lime and the wall. Shuttering is then screwed to the rails and the mixture is placed in by hand. Photo credit: Billy Aiken.
Material is then tamped down gently; the desired density is 150-200kg/m3, which is considerably lighter than that used for hempcrete walls. Photo credit: Billy Aiken.
View from above showing the shuttering, the material and the underlying slate wall. Photo credit: Billy Aiken.
The shuttering can be removed immediately and moved up the wall to do the next lift, as the mix is strong enough to support itself.
Close up of the finished material, cured and ready to plaster.
Finished and plastered, with viewing window.

In this installation, thickness varied depending on the wall, and it can also be varied along a wall to level it up. The material is also suitable to cast around curves and into fiddly corners and it can be trowelled directly onto the wall; it is much easier in this regard than any of the breathable insulation board options. More on the details of the material another time…

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