Little boxes on the hillside

Sometimes it makes more sense to begin the story at the end. As part of the BEACON project, I’m interested in improving cast internal wall insulations suitable for renovating solid wall buildings. These systems are designed to provide insulation value, should be vapour permeable, and via increasing the surface temperature of the wall and buffering indoor moisture they can potentially reduce problems with damp and mould growth. Durability, sound insulation and ease of installation are also factors. We can get a reasonable idea of how well a material will fulfil these criteria by undertaking laboratory tests. So we need to create test samples, and that is where this story begins, with help from Simon James Lewis of Neighbourhood Construction.

The aim was to create moulds or some kind of formwork that we can fill with the cast material, allow to cure, and then remove from the material allowing it to be tested for various characteristics. Ideally the formwork would be reusable, cheap to produce, and easy to assemble/disassemble. Some kind of wooden box therefore seemed like the best approach. This is where Simon’s background in three dimensional design and cabinet making came in handy. Whilst I’m reasonably confident with woodworking tools, craftsmanship is not my strong point, so I made coffee whilst Simon got on with the tricky stuff. A few artful scribbles and calculations later, he was off to the bench saw and what emerged was the elegant and simple solution.

Cast internal wall insulations typically consist of a cementitious binder (often lime rather than cement), and a lightweight plant-based aggregate. The material of choice to mix with the binder in this application has historically been hemp shiv, which was a by-product resulting from the use of hemp in rope and textiles. Hemp shiv seems pretty well suited to cast internal wall insulation, however, there are plenty of other plant materials that might do as well or better, so it is perhaps worth taking a fresh look at this question. And being surrounded by plant scientists who spend decades breeding plants with particular properties, I sometimes dream of a future where we breed plants specifically for building applications. I’ve written a bit about this here.

Let the playing begin

Having created the formwork, it was time to get creative with making mixes of materials to fill them with. This was simple play; rather than starting with any preconceptions of what was best, we took whatever materials were at hand in order to see how well the formwork functioned and what material ratios might be appropriate. On the day, this turned out to be a variety of straw-like plant materials and then some more unusual materials including pyrolyzed and steam-exploded plant matter, popcorn, and dried cherry stones. Sadly, the beetroot charcoal (it had been left in a rayburn and forgotten about for too long) didn’t make it as far as a block. Learning through play both allows a lot of iterations in a short period of time, and also provides the opportunity for happy accidents which could lead to new products and applications.

Bioaggregate samples in formwork. The tidiness is misleading; we had swept away all the detritus from failed blocks by this point. The disks in the foreground are plaster samples. I blogged about this here.

The formwork itself held together well with rubber bands and was easy to fill. After a couple of hours drying time, the base and the lid could be removed to allow more airflow and accelerate the curing process. The formwork was easy to remove, and can also be used to protect the block for easy transport. All in all, a neat design, and will allow us to move on to testing the properties of different formulations of cast bioaggregate.

This post is based on work enabled by the BEACON project, which is funded by the European Regional Development Fund via the Welsh Government.

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