lime wash – How to make a hot mix

The finished limewashed house

We just finished applying a hot lime wash to our ‘Ty Twt‘ building in Wales. Here you can see the finished building.

Ty Twt with its final coat of hot lime wash.
Ty Twt with its final coat of hot lime wash.

Ty Twt is a load bearing straw bale house completed by my company, Hartwyn using our intern building model. The house was completed in 11 weeks in 2016, with a final weekend to finish up the lime and green roof just completed in July 2017. Continue reading

Natural floor insulation

Thermofloc is a natural floor insulation. Made from cellulose that has added minerals to make it fire retardant. It is simple to install and is much more affordable than any other natural insulation we found.


double whisk mixer

To break apart the insulation blocks we used a double whisk mortar mixer. By using an online calculator to work out how much we needed for our floor dimensions, we could be sure to achieve the correct density and therefore U-value.


NaturePlus – Thermofloc is the first cellulose insulation to be awarded the coveted NaturePlus mark of quality and sustainability.

  • Laid density of 40kg/m3
  • Thermal conductivity 0.039W/mK
  • Fire classification as per EN13501-1
  • Free of hazardous substances as defined by ETA-05-0186

Assessments show Thermofloc does not provide a suitable habitat for rodents and as such rodents will avoid nesting within the insulation.

Straw bale building – The how to guide

In straw bale building we use a few key techniques that are unique to the trade.

Around our windows we have posts, so we need to put a notch in our bales to fit them snugly.

We do this using a Dewalt Alligator saw which is made for cutting building blocks, wood, drywall, insulation and Class 12 clay blocks. It also cuts straw bale very nicely, without throwing up a lot of dust.

I have also used a chainsaw to do this job. While the chainsaw does do an excellent job, it’s certainly more dangerous and a lot louder, plus throws dust into the air.

Here interns, Brendan and Rowena show us how it’s done using a template to ensure the right size notch. (Music by Money Mark)

Tools for straw bale building

straw bale building tools

Here we see our beautifully constructed straw bale walls. In front of them, two of the tools of the trade.

First up, we have the persuader. This larger than life hammer is used to knock the bales into alignment.

Secondly, we have the baling needle. This is threaded with twine and passed through the bales like a giant knitting needle in order to re-string the bales to custom sizes.

Dressing the Bales

dressing the bales

The first thing we do to our bales is to dress them. This means we physically manipulate the straw in the end of the bale to make a flat and square end. This means our bales fit together better with fewer air gaps.

Our Natural Building Interns

Hartwyn natural building interns

Long overdue group shot of our fantastic natural building interns!

Introducing (From the left): Me, Brendan, Rowena, Blythe, Jake & Jamie.

This is the team doing the bulk of the work. They have given up 8 weeks of their lives to come and build this house. I’m so very proud of how far they have come and what they have created.

We are now getting into finishing land, so i’m really excited to unleash them on the clay and trowels!

Locally sourced materials

It is important to us to build with locally sourced materials. We have lots of clay, so are utilising that as much as possible. If this build were elsewhere in the country we would be choosing a different approach. We can’t just have a template for a ‘sustainable home’ that doesn’t factor in what local materials are available as transportation accounts for a huge amount of energy usage.

our straw crop is locally sourced
Our straw crop – a few days before it was baled (Photo Jake Chadwick)

Our locally sourced materials

  • Our straw comes from a farm less than 5 miles from the site. We were able to go to the farmer, check the size and density of the bales… and even request that they be made as tight as possible… which they did! (The even cranked it so hard the baler broke – once the part was replaced, fantastic dense bales were the result – The best I have ever used!).
  • Most of the timber is from a local saw mill, using locally sourced timber.
  • Our gravel and sand is from a local pit.
  • The sheep wool insulation is all from Welsh sheep.
  • We are making clay plasters from clay dug on site.
  • All of our lime comes from Ty Mawr Lime, 60 miles away.

These are our obvious success stories….

Not so local

We have not been able to source everything locally, our smartply for example, came from the Czech Republic. Not great!

Other considerations

There have been other more subtle design choices that have allowed us to use more local materials. An example of this is how we have sheeted the roof. The conventional way is to use 18mm ply sheets, usually shipped across the country, if not Europe. We have opted to use larch planks from our local saw mill – It takes longer to build, but the environmental impact is far better.

More reading

Car tyre foundations – Video

Car tyre foundations team

This week we have been laying our car tyre foundations for our #BalesInWales cabin.

We have chosen to use gabion basket foundations. Though our Gabion baskets are reclaimed car tyres.

Car tyre foundations are the perfect choice for this build as:

  1. They are cheap – actually the tyres are free, local garages have given all the tires we need as they have to pay to have them disposed of. We are only paying for the pea gravel to fill them.
  2. They make a capillary break – Rising damp occurs when a porous material is used as a foundation. To combat this, conventionally a damp proof membrane (plastic sheet), is used to stop moisture coming up in the wall… but what if any moisture gets into the wall from above? It creates a paddling pool which our bales would sit in. Because neither pea gravel or rubber is porous, moisture can only travel downwards with gravity.
  3. They find a use for an otherwise problem material. Tyres are said to have a life span of 30,000 years, so disposal is a big issue.
  4. They are low embodied energy. To turn a tyre into a foundation, just takes the pea gravel and some porridge to power our workforce!

This last week we have been happily filling our car tyres in neat stacks, here is intern, Jamie showing us how it’s done!

Foundations Video from JeffreyTheNaturalBuilder on Vimeo.