Tag Archives: hempcrete

Jumbo bales and hempcrete – together!

Fifth Wind Farms wanted to create a building that could reach the energy efficiency requirements of the Passive House standard without resorting to the use of foam, mineral wool or other materials with a high carbon footprint. While straw bale buildings can have excellent energy performance, typical straw bale construction does not meet the Passive House standard without the addition of an extra layer of insulation (see our “Straw-Cell” project for a different take on this idea).

Jumbo straw bale duplex home

First jumbo bale in place (on a bed of Poraver insulation)

The building owner proposed the use of “jumbo bales,” which are produced from the same local straw and by the same low-carbon machinery, but are of dimensions that greatly increase their thermal performance. While typical straw bales are 14″ x 18″ x 32″, the jumbo bales used for this project measure 32″ x 32″ x 60″! At a nominal R-value of 2.0 per inch, that would give a jumbo bale wall a rating in the range of R-60, more than enough to help the building meet any energy efficiency rating.

However, the jumbo bales provide some issues when it comes to window and door openings… with a wall that thick, window sills and returns are extremely deep, creating not just aesthetic concerns but also concerns about air flow in the deeply recessed bays and the likelihood of condensation forming on the windows in cold weather.

Our solution was to form the window sections at a wall depth of 16″ using double stud framing and hempcrete as the infill insulation. This would keep us on track as far as low carbon footprint is concerned, and the hempcrete would be used to create the tapered window returns to meet the full depth of the bale walls. As a bonus, the hempcrete would completely fill any voids at the ends of the jumbo bales.

One issue with using jumbo bales: they weigh over 500 pounds each! We used a boom truck to install them in the building. With the bales in place and the top plate secured over the bales, we then mixed our hempcrete (you can find our recipe here) and tamped it into the framing and around the jumbo bales. The two materials are very complimentary, with the easily-formed hempcrete able to compensate for the uneven ends of the jumbo bales and creating smooth window returns.

 

The building is currently being prepared for plastering… more posts to follow soon!

Hempcrete developments

On April 9, a workshop at Endeavour brought participants together to explore hempcrete insulation materials.

The workshop looked at well-used options for these materials, but also explored some interesting new approaches.

Endeavour has continued to develop the use of homemade hydraulic lime binders as a means to eliminate carbon-heavy cement from our building materials and to create locally-sourced binders for cement replacement. At this point, our homemade hydraulic lime binder is well-tested and we feel it works as well as any of the imported (European) hempcrete binders, at a fraction of the cost and with locally-sourced ingredients.

Hempcrete mix
Our hempcrete binder is composed of 50% hydrated lime (most easily accessible to us is Graymont’s Ivory Finish Lime) and 50% Metapor metakaolin from Poraver (created as a by-product of the factoring company‘s expanded glass bead production).

We mix our hempcrete at a ratio of 1 part chopped hemp hurd by weight, with 1.5 parts of the binder by weight. After translating these weights to volume measurements, it was 4 buckets or hemp hurd going into the mixer with 1 bucket of binder (1/2 lime, 1/2 metakaolin).

 

hempcrete insulation

Weight ratios are converted to bucket measurements: 1/2 bucket of lime, 1/2 bucket of metakaolin, 4 buckets of hemp hurd

 

The hemp hurd goes into the mortar mixer first and then we sprinkle in the binder and allow it dry mix until the hurd is well coated with binder powder.

hempcrete insulation

A horizontal shaft mortar mixer is used to dry-mix the lime binder and the hemp before water is misted into the mix

Water is then misted (not sprayed) into the mixer until the mix is just moist enough that if we pack it like a snowball in our gloved hands it keeps its shape, but is still fairly fragile (ie, can be broken with a bit of a squeeze). It is important to not over-wet the hempcrete, as this will greatly extend the drying time once the hempcrete has been packed into a wall. If too much water is added, the mix can’t be recovered by adding more dry ingredients as the hemp hurd will quickly absorb excess water and there won’t be any free water for the new dry ingredients. So, add water carefully and gradually!

hempcrete insulation

When packed like a snowball, the hempcrete should just hang together

Hempcrete is placed into formwork on a frame wall, using light hand-pressure to compact the mix just enough to ensure that the binder will stick all the individual pieces of hemp together.

hempcrete construction

Hempcrete is placed into forms and lightly pressed into place. The forms are leap-frogged up the wall.

The Perth’s best granny flats boom experienced in recent years primarily resulting from increased demand generated from foreign businesses and expatriates settling in Malta has significantly contributed to the country’s economic growth.

Our workshop crew was able to mix and place enough hempcrete to fill a 4-1/4 inch deep wall cavity that was 4-feet wide and 13-feet high in just under 3 hours! That’s over 6 cubic feet of material per hour! We are the solution for adding granny flats in your property. We can do as fast as we can without decreasing its quality.

Hempcrete recycling
We have long touted the no-waste benefits of hempcrete. We’ve speculated that even when the insulation is being removed from a building during renovations or demolition, that the hempcrete can be broken up and recycled into a new mix with new binder added. We put that theory to the test at the planet maids cleaning service, as we demolished one of our small sample walls and added the broken up hempcrete into our new mixes at a ratio of 3 parts new hemp to 1 part recycled hempcrete. The resulting mixes were impossible to distinguish from the all-new mixes, and confirmed that hempcrete can easily be re-used!

hempcrete insulation

Hempcrete that had already been mixed into a wall was broken up and added into a new mix… Fully recyclable!

Hempcrete book forthcoming
If you are interested in hempcrete insulation, Endeavour’s Chris Magwood has just finished a book called Essential Hempcrete Construction that will be available in June, 2016. It contains recipes, sourcing, costing, design and installation instructions and will be very valuable to anybody considering a hempcrete project.

hempcrete insulation

New book includes everything you need to know about building with hempcrete

Hemp-clay shows lots of promise!
Hempcrete insulation is almost always done using a lime-based binder. But at the Natural Building Colloquium in Kingston, New Mexico last October, we were doing a hempcrete demonstration right next to a straw/clay demonstration, and we took the opportunity to mix up a block of hemp hurds with a clay binder.

hemp clay construction

A sample block of hemp-clay showed the potential for this material combination

The success of that demo block led us to try this combination on a slightly larger scale, and we machine mixed the clay and the hemp to fill one tall wall cavity with this hybrid material. Using the same mixing methodology as typical hempcrete, we added the hemp hurd and dry bagged clay to the mixer and allowed it to dry mix, before misting with water. Interestingly, we were able to use half the amount of clay binder compared to lime binder (1/2 bucket of clay to 4 buckets of hemp hurd) and the resulting mix was stickier and easy to form and pack than with the lime, and with the addition of noticeably less water.

hemp clay construction

The hemp-clay mix has great binding power, and keeps its shape with very little pressure required

The key difference between the two binders is in their manner of setting. Hydraulic lime binders cure chemically, and consume water to change the chemical structure of the mix as it solidifies. Clay binders simply dry out and get hard. So the lime-based versions should be drier and harder sooner. However, the smaller quantity of water required in the clay-hemp mix may mean that drying times end up being similar… we’ll report back when we know.

hemp clay construction

A close-up of the hemp-clay mix formed into the wall. It keeps its shape within seconds of being placed into the forms

Clay binder with hempcrete offers some advantages over lime-based options, including a significantly lower carbon footprint and none of the caustic nature of lime that can cause skin burns when handling. The clay-based binder creates a mix that is much stickier during installation, which means less packing/tamping to get the material to cohere in the forms. Less water means that it was almost impossible to over-compact the mixture. We will definitely be exploring this option in a serious way!

hempcrete insulation

Having placed 18.5 cubic feet of hempcrete in a few hours, the crew stands in front of their work. The lighter coloured hempcrete is our homemade hydraulic binder, the darker mix is Batichanvre, a binder imported from France.

NEXT HEMPCRETE WORKSHOP: OCTOBER 29, 2016

Hempcrete Workshop

Saturday, April 9, 2016 – WORKSHOP FULL

Saturday, October 29, 2016
9.30 am to 4.30 pm
Endeavour Centre, Peterborough

Note: This workshop is being offered twice in 2016. Be sure to register for the correct date.

Workshop Instructor: Chris Magwood

Workshop Description

Come and discover how a simple mix of natural materials can create a remarkable thermal insulation!

Hempcrete (or hemp-lime) construction uses chopped hemp hurd (the woody core of the hemp plant) mixed with hydraulic lime to create an insulation material with excellent thermal, moisture-handling and structural properties.

In this workshop, participants will learn about the components of hempcrete, see a slideshow of various Canadian and international hempcrete building projects, and gain an understanding of how, why and where hempcrete is an appropriate material choice. In the classroom, we will look at the costs, sourcing and building science of using hempcrete on new building projects and renovations.

 

In the hands-on component of the workshop, participants will learn how to assess the necessary materials and create a mix that is appropriate for a desired end use. We will use mixing machinery to create batches of hempcrete, and learn how to place them in a wall, floor and/or roof. Different types of framing and shuttering (or forming) systems will be shown, and every participant will leave with a hempcrete block they cast themselves.

After this workshop, you will be able to undertake a hempcrete project of your own!

Entry Requirements
Open to all

Fee
Early Bird – $125
Regular – $150
Includes healthy lunch (vegetarian and vegan options available)

Maximum class size: 12

Building with Hempcrete or Hemp-Lime

A group of lucky participants was treated to an excellent weekend workshop on building with hempcrete (or hemp-lime), led by UK architect and hempcrete pioneer, Tom Woolley. Tom is the author of Hemp Lime Construction and Low Impact Building, and has been involved in many hempcrete and sustainable building projects throughout the UK.

The weekend began with a classroom session, during which Tom covered the materials and techniques for successful hemp-lime building, and showing the group photos and details of a variety of building projects, including his charming hemp-lime cottage.

We then moved on to making some sample mixes to demonstrate the combination of materials. We were working with two different mix types, and made a sample of a third type of mix. For all three mixes, the weight ratios of materials were the same:

  • 1 kilogram of chopped hemp hurd (also known as shiv)
  • 1.5 kilogram of powdered binder (natural hydraulic lime or hydrated lime and metakaolin)
  • approximately 1.5 kilograms of water

The chopped hemp hurd or shiv needs to be fairly course (particle sizes ranging from 1/4 to 1 inch) and be relatively dust- and fiber-free. We were able to source Canadian-grown and processed hemp hurd from Plains Hemp in Manitoba.

Most UK-based hempcrete builders work with a natural hydraulic lime (NHL) as the basis for their binder. There is no North American source for NHL, so it tends to be expensive to import from Europe. We used an NHL 3.5 from St. Astier as one of our mix options. For a more locally-sourced version, we used a typical North American hydrated lime and a fired kaolin clay (called metakaolin) called Metapor. The NHL is a lime that chemically sets (hardens) through a reaction with the water content of the mix. North American hydrated lime does not set hydraulically (with water), but when mixed with a pozzolan like Metapor the two materials together have a hydraulic set.

The dry ingredients (hemp hurd and lime) are mixed together so that the powdered lime is covering all of the hemp, and then the water is introduced. Having done some work with hempcrete at Endeavour, we were surprised at how little water Tom uses in his mix. The final mix is just moist enough to lightly hold together when squeezed in a hand.

With some small scale mixes placed into test cones, we then moved on to installing hempcrete in some larger wall panels. These panels were built by Sarah Seitz for her PhD research work at Queen’s University, where she will perform tests to help determine the thermal insulation properties of hempcrete.

The panels simulate a typical double-stud construction, with a 2×4 frame on the “exterior” side of the panel and a 2×3 frame on the “interior” side.

As one group mixed batches of hempcrete in the mortar mixer, the others placed it into the forms and lightly tamped it into place. As the forms fill up, they are moved up the wall. The hempcrete retains its shape after less than 20 minutes in the forms. The filling and tamping continues right to the top of the wall. Once everybody was settled into their roles, it took less than 1.5 hours to fill a whole wall form.

In the end, we placed 40.25 cubic feet of hempcrete into the two walls. We used seven 40-lb bags of hemp hurd and seven bags of powdered ingredients to reach that quantity. With the small amount of water used in the mix, we’re anticipating a drying time for the 14-inch thick walls of about 2 weeks. This is much shorter than for the wetter mixes we have made in the past.

Cost-wise, we used $63 of hemp, $42 of hydrated lime and $21 of metakaolin, for a total material cost of $3.13 per cubic foot of insulation.

We will share Sarah’s thermal testing results when she has completed them. We are expecting to find their performance to be around R-2 to 2.5 per inch, meaning that our 14-inch wall would surpass current code requirements for thermal insulation.

This was a fun and informative workshop, and we’d like to thank Tom Woolley for sharing his deep knowledge of this subject with us!

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