Monday, 9 March 2015

Back to The Green Backyard for Straw Bale Building

A few weeks ago we spent a very enjoyable weekend at The Green Backyard in Peterborough, building a cob oven.
This proved to be quite a task which continued into a second weekend. Unfortunately Sue and I could only make the Saturday, so we missed the final day putting the finishing touches to the outside of the oven. This is done with a looser mix of cob, mixed with finely cut straw.

Anyway, I'll cut to the chase.
Here's the rather amazing finished oven.

When Sue and I learned that Alan Eley, who usually works at Hill Holt Wood, was coming back for a third weekend to help build a straw bale wall, we were keen to return. Again, we could only make one day of the weekend, but this time we missed the right day! For a hardworking band of volunteers and course participants spent Saturday laying the foundations. These were basic, just a treated wooden frame into which earth was compacted... and more earth... and more earth. It's surprising how much earth you can fit into a hole! Again, it was subsoil which was required. You don't really want to be building any sort of wall on top of seed-filled topsoil.

So when we arrived here's what we found.

We also found Alan mixing up a wheelbarrow of strange white powder and beseeching us to stay upwind of the dust which was flying everywhere. It has to be said he looked like a wizard!

This was hydrated lime, being mixed with water to form a putty. Later this would in turn be mixed 1:3 with soft sand to make the lime render. Using this is preferable to cement as it allows the walls to breathe. It's also not quite so energy inefficient to produce as is cement.

Membrane between foundations and bales

The hazel stakes which secure the bales in place

We then proceeded to carefully place straw bales onto these foundations, secured with hazel stakes. It's just like giant lego really.

However, if you've ever built a wall (even lego) you'll know that you need half bricks at the end. Fitting straw bales into an existing frame requires various fractions of straw bale, but it's not as simple as just cutting them. For as soon as you cut through the baling twine which binds them so tightly, they quickly expand out into the available space.

Alan demonstrates
splitting a bale

Therefore some technical skill is required. Alan explained how to thread a straw bale needle through to split the bale into two and secure it tightly. At first this seemed like a baffling art which only the initiated could succeed at.

However, the key was to actually have a go at it ourselves. With a bit of a lead and some common sense, it all came together.

Having mastered all the requisite skills, the wall was erected in no time.

Before it could be rendered,
a quick hair cut was in order.

The final bale goes into place

After sharing a communal pot of soup, we returned to begin the rendering. There were plenty of experts on hand, but it was really a case of just getting it to stick however you could.

Sue and I had to leave before the first coat was completely on. Altogether the wall will get three coats of render. We'll return to see the finished product when the cob oven gets fired up.

Meanwhile I am working on plans for a straw bale pig house, possible even with a living roof. I was impressed with the cob, but the straw bale walls blew me away. Maybe that's the wrong phrase for a house made of straw!

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