Lime Mixing for Stone Piers × Reciprocal Roof Update – Does Lime Perform Better than Concrete? – Hobbit House Build

 In Blog, Student Post

The 3rd week of the hobbit house build summed up in 3 words: lime, roof, rain.

Building with Lime – Stone Piers

The first classroom session of the week (held by none other than Mr. Hart) was all about lime. How and why we use it as a building material and its ‘life’ cycle. It is very interesting, especially if you compare lime to concrete and how they perform on a building. In this hobbit house build we are using lime for the stone piers and external rendering. Lime is moisture permeable, meaning it allows the moisture of a household (cooking, showering etc.) to escape. In comparison, cement has no ability to deal with water, which leads to dampness. Also, every building moves over time. Since lime is flexible, plaster and render made with it don’t crack. Cement is inflexible and doesn’t move with the building, thus you can see a lot of cracks on the older  buildings that have been rendered with cement.


The Lime Classroom

The Lime Classroom


After theory comes practice – we slowly and carefully added water to a quicklime and sand mixture to make ‘hotlime’ mortar. Quicklime reacting with sand forms a stronger bond than if we mix slaked lime with sand. But when quicklime reacts with water it produces a huge amount of heat. The quicklime dust is dangerous if inhaled and the mixture can irritate or burn the skin. So always use protective glasses, a face mask and gloves, along with protective covering for any exposed areas of skin.

Mixing demonstration

We started building the piers for our posts: stacking locally dug stone and binding them with the hotlime mortar.

Students working on piers

Students working on piers

Students working on piers

Reciprocal Roof

We worked on our reciprocal roof as well. Reciprocal roof frames are self-supporting structures. The intertwining nature of its parts creates a complimentary tension which makes the self-supporting roof remarkably strong. It’s easy to build in theory, but when the timbers are massive and there is not enough people, it gets quite tricky. It took us a lot of practice, calculating, planning… Trials and errors.

First we practiced making our reciprocal roof on the ground. We had to check how the different bits and pieces that we’ve cut work together, so that we could mark our rafter joint cuts and adjust what we’ve cut.

Once everything will be in place, we will secure the timbers with bolts.

It’s been raining all week, but the sun seems to be returning. Fingers crossed for a sunny weekend!

The Hartwyn Team

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