Straw bale house walls get external render

 In Blog, Student Post

It’s been another big week for the Hartwyn crew, with some fantastic teamwork and strong input from everyone involved. Joe and Jeffrey have been setting some ambitious targets, and the team have risen to the challenge, growing in confidence and skill as each new stage has been tackled. The house has been changing dramatically every day, and this week has seen the roof become fully insulated and water tight thanks to Joe’s consistent efforts.

Jeffrey has been putting in a heroic and tireless job building all the windows from scratch. That’s enabled “straw master” Jodie to coordinate the students in straw-clay land. There’s been a lot of footage for Dewi, and he’s been skipping around the place catching the action first hand.

Here’s a day by day summary of that action…

Light Straw Clay
Monday 27th August:

After a wet weekend, the return of some dry weather felt really comforting and uplifting. If you’ve been keeping up to date with last week’s posts from Sam, you’ll know we started to fill the gaps between the top of the bales and the roof boards using a light straw clay mix (more affectionately named “stray claw”). This essentially extends the walls to the level of the ceiling – thus helping seal the thermal envelope. The light straw clay has a slightly lower insulative value than the bales, but is still quite efficient.

Having cut our teeth on Friday, we began to move increasingly rapidly as one team processed and stuffed the light straw clay into place, whilst a second team were supporting their progress by building and advancing the chipboard form-work. It’s amazing how efficient a task can become when there’s a whole team involved and finding their flow.

Outside of the building there was a continuous stream of clay slip being made by mixing water with the subsoil dug out for the foundations. Stones were removed by throwing the soil through a screen into a wheelbarrow. The slip was of a batter type consistency. Earth to wall!

Final mention to the windows, today some of the subframes were fitted, into which the windows will sit. Just prior to this there was the fiddly work of sewing in the bale ears, trimming back oversized ears, and adding straw packages to bulk out any undersized ears. This work makes the bale edges much more stable and uniform up to the subframe. By the end, the form and light straw clay teams had linked the wall and roof around half the building. A fabulous day!

Sam demonstrating good form as he digs through the mountain of soil, later used to make light straw clay.


Perlite insulation on the reciprocal roof
Tuesday 28th August:

The light clay straw team (aka “wet hands crew”) were given the challenge of filling out the rest of the wall / roof interface, something that they seemed to take-on with great enthusiasm! Forms were rapidly going up and light straw clay was being stuffed heartily into the cavities – a well soiled team! As with pretty much all of the new skills on the build, the mixing of the clay and straw seemed to go through an evolution of proficiency and efficiency as working hands became more accomplished and familiar with the new materials.

I love seeing new techniques develop and spread through the culture of the group. Jargalan even bought dance into the mixing technique, churning out more and more light straw clay with each groove!

Tuesday also saw a fair sized mountain of perlite bags ferried up onto the roof and laid out carefully to form a load bearing insulation layer. Near the centre of the roof the bags needed taping together due to the steep pitch. Kirk and Mike were given the special mission of sealing any gaps between the bales and stonework with wool insulation and then pointing with a good layer of lime mortar.

Rowan put in an incredible day, keeping the whole wet hands team fed with delicious clay slip of the finest quality! Sam and I completed the sub-frames for the remaining windows, thus preparing the space for Jeffrey’s impressive looking windows. Needless to say, the form team and wet hands team reached their goal and the second half of the house was completed with light straw clay.

A big thanks to Mattieu for hosting the evening with his extensive knowledge and expertise with a presentation about the politics of climate change. Everyone seemed wholeheartedly engaged. I personally liked the way he presented the material in a matter of fact way. The truth may be alarming, but I agree with his take home message that we would be foolish to pretend the call for radical action, now, was anything other than urgent.

The roof changed dramatically once the perlite insulation went on.

Looking inside the building, you can see the wall / roof interface is now complete with the light straw clay bridging the gap between the ladder and roof boards.


Plaster key coat on the straw bale walls
Wednesday 29th August:

The great reveal! Time for a change of focus – we began the day with some tuition from Jodie and Jeffrey. Essentially we needed to create a “key coat” or “reveal coat”, using a clay slip and forcing it into the fibres of the bales with palms and later fingers. The idea here is to create an intermediary surface onto which the plaster can stick – hence the name “key” coat. This process also enables any gaps to be revealed, and any loose straw is allowed to fall out – hence the other name “reveal” coat.

Big aim of the day… key coat the whole outside of the building! Not only did we manage that in its entirety, but Joe, Kirk and Mike covered half the roof with EPDM (pond liner rubber) as the main waterproof layer. In other areas, Flo used her carpentry skills to complete new frames above the outside of the kitchen windows and front door. In clay land, Sam became a pro on the mixer with his tai-chi style movements.

Toward the end of the day, Kirk whizzed round with a hammer and knocked clout nails into timber for later covering with light straw clay. Having completed the key coat early, the rest of the team began to fill revealed holes with light straw clay. The day’s mission complete!

The evening bought an unexpected visit from our woodsman Henry. Lots of us were entertained and impressed by his didgeridoo and very basey deer-skin drum. The starry camp echoed with the deep and primal beat of the drum, lit-up by the flickering flames of the campfire.

Rowan and I getting to grips with the reveal coat.

Dubbing out the straw bale walls
Thursday 30th August:

On a run after three very successful days, we started with another new skills briefing. Straw master Jodie gave us the lo-down on filling out the walls and repairing revealed holes. It seemed easy enough; wet the wall, apply the straw clay mix (this time wetter than the light straw clay used above the bales for a better stick) and smear with the heal of the hand.

As well as that, the walls needed to be made straight, so any divots or inconsistencies were to be filled out. After completing the speedy key layer of Wednesday, I think I was one of a number of us that were lulled into thinking this would be another rapid job. Unfortunately the poor bale structure and rounded walls meant there were a lot of spaces to fill!

Mike was diverted to work with Joe finishing the waterproofing of the roof with EDPM – a momentous occasion! I framed up the inside of the kitchen window and front door for later infill with stray claw. Jess put her sanding and priming experience to good use by preping the new window frames for installation.

Joining the team outside, I became quite engrossed in bad puns about mud and straw in a Yorkshire accent, and our designated clay-straw mixer became a take-away chef… I think tiredness was setting in! Despite that, another pleasant campfire under the stars and rising moon finished the day on a high note.

Jodie and Jess look on at the task at hand. You can see the “Holey” areas of the wall hat were revealed by the key coat. The next phase was to fill those in and level the wall ready to receive the plaster.

Windows get installed
Friday 31st August:

The first frost this morning!! It may have only been very light, but there was definitely ice in the grass at 7am! Autumn is rapidly approaching. So after a day of slower progress yesterday, we were given a few more tips on completing this stage of the build. The process of adding straw clay to straighten the wall using a straight edge is known as the “dubbing out coat”. This is very important in enabling the plaster to be applied easily and with equal thickness throughout the wall. Though that may not seem significant, I’ve learned that thicker plaster takes longer to dry, thus creating weak points for cracking in the margins between dry and wet (thin and thick) plaster.

Completing the wall to a higher specification required us to step back more and take a look along the line of the wall to see hollows and inconsistencies. With new detail, the team continued Thursday’s work with more insight and an image of what was needed.

Meanwhile, inside the roundhouse, Rowan and I had the specific mission of filling in the space above the kitchen window with stray claw – something that we just about managed by the end of the day. Eleanor became head-chef in the straw mixing department, and did a fabulous job keeping up with all the orders!

Toward the end of the day the windows were ready for installing, so we had a full demo of the process as Joe talked us through the useful qualities and potential pitfalls of using lead flashing (pliability, weather resistance, easy to reuse, but also a poisonous heavy metal – not good for rainwater collection!). The windowsills are made of larch, a tough & durable softwood. Within the final hours two windows were installed and yet again the house was taking on a new beautiful form. What a phenomenal week!

Jargalan putting some finishing touches onto the dubbing out coat. The window frames are now in too!

Wow, the practice of writing this blog has really highlighted how much amazing work is going on! It’s quite incredible to be a part of such a fantastic process. How rewarding and satisfying to be learning and applying new skills and watching the impressive house morphing more and more into a beautiful home. I hope you’ve enjoyed the update. Tune in again to see what happens as we move into weather sealing the walls next week.

Hartwyn Natural Building Course

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Many thanks, the Hartwyn team

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night sky above hartwyn build