The building has undergone another huge transformation in the past week or so, largely because the straw bale walls have started to be covered with their dressing of Lime render.
We are using Lime for a number of reasons. Firstly it is a breathable material, it will help the building lose moisture and thereby protect the timbers and straw. It acts as a natural rodent and insect deterant, which will be beneficial for our straw bales. Also it means we can avoid using cement, which is an extremly environmentally harmfull product. Cement and concrete have huge costs in terms of carbon dioxide. Lime also produces greenhouse gasses in its production, but unlike cement it reabsorbs CO2 as it sets. It gives a very different asthetic to the building compared to cement, it is a traditional material which has been used in building for centuries and gives a more natural look and feel.
The Lime render was mixed on site in a specialist mixer.
The first coat was then applied to the bales by being blown on with compressed air.
This forces the lime into the surface of the bales to form a really solid bond. The timbers in the walls were covered to avoid them from being coated with lime during the process.
A second coat is now being applied by hand, this coat contains goat hair to help keep it well bonded and strong, the final finish will be achieved with a third coat which will also be trowelled on.
Where we have a verandah protecting the walls their surface will be lime render, some of the building is more exposed to the elements though, and on these walls we are using oak weatherboards. The straw bales were built up against softwood studwork, lime mortar was used to cover the bales, a breathable membrane was then tacked on and the membrane is now being covered with boards.
The boards were cut on our mill using oak from Swan Barn Farm. Our weatherboards are feather edged, as you can see this means they are triangular in section, the thicker part of each board overlaps the thinner section. We wanted to use these boards partly to tie the building in aesthetically with the existing basecamp, but I also really like the way the square edges of the boards look against the roundwood of the frame and the the lime render.
The feather edge effect is created by placing a jig on the mill, after every pass of the saw the jig is turned to tip the block of oak one way or the other, this means the next cut is at a slight angle to the previous one giving the triangular section to the boards.
Each board only has one row of nails put in as it goes up, this will help to prevent them from splitting as they dry out. The top of the board is then held in place by the board which sits above it.
Its a lot of work to get it right and produce good quality boards, but I think they look great, this is the side of the building that you see as you arrive, and I think it will create quite an impression.
Last week we had another group of working holidays volunteers come to help on the project, thanks very much to all of them. They made another load of shingles for the roof, and amongst other things also christened our new charcoal kiln. We have been making charcoal here for a number of years, its a really useful way of using up offcuts of wood and less desirable species from the coppice and has great green credentials. We sell charcoal on the site and it is used by our volunteers for their barbq. I have always thought food can provide a useful introduction to environmental issues, and cooking your burger over some sustainably produced charcoal is a very good introduction to woodland management issues. For the last few years we have been borrowing a kiln, but now, thanks to a kind donation from local supporters group the Three Counties Association we now have one of our own.
The guys used up some of the alder which came out of the coppice last winter for the first burn. The process effectively removes the water and other volatile compontents from the wood by cooking it in the absence of oxygen, what is left behind is mostly the carbon structure of the wood. As well as making a great product for cooking your burgers the finer particles can be used as a soil conditioner in your garden, it holds in moisture and locks away carbon dioxide.
Its always interesting to see how much the volume of the produce in the kiln reduces by during the process, it was full at the start of the burn, but close up you can still see the structure, grain and even the bark of the wood.