The Basics of a Cast in Place Hempcrete Wall
We are beginning to see an increasing trend of homes being constructed with hemp lime concrete.
What is Hemp Lime Concrete?
Hemp Lime Concrete, also known as Hempcrete is a unique building material, being a composite of a bio-fibre (hemp hurd or shiv) and a mineral binder (lime). These ingredients are blended together with water, and the moistened binder coats all the particles of hemp shiv.
Carbon Capture
The plant absorbs a lot of CO2 through it’s lifecycle and stores it into the wall.
High R Value
Hempcrete has an R-value of 2.4 to 4.8 per inch, compared to 0.1 to 0.2 per inch of concrete.
Thermal Mass
For the season of summer, it stores heat in the wall during the day and releases it at night. Most houses built with hempcrete do not need an AC.
Sound Absorption
Used on external and internal walls as a great sound absorber.
3 in 1
A Lime Plastered hemp wall acts as: Exterior wall, Insulation and Drywall.
Moisture Control
Mold and moisture build up can destroy a structure but the hempcrete wall is breathable which makes a big difference. The “breathable” wall.
Fire Resistant
Hemp is great at resisting fire and has been proven to respond well in fire situations.
How is Hempcrete used to build a home?
Since there are many ways one can make a home with hempcrete, in this article we will assume that you are building a standard home made with hempcrete with basic components, ideal for mist climates around the planet.
Hempcrete is not used for structural support and is actually used in combination with structural lumbar.
(A) Lime Plaster
- This type of plaster is made of sand, water and lime.
- A mixture of lime and sand taken in equal proportions in a mortar mill, mechanically prepared with water to make a paste of required consistency.
- It is vapor permeable which helps to create a “breathable” wall.
- Can be used on interior or exterior.
- It is a natural material and it’s usage can be traced back to 7,500 BC.
(B) Cast in Place Hempcrete
The Process
- Mix the Hempcrete onsite and make the product ready
2. Have the wall in fill area ready with formwork
- The form work is placed in one section at a time. Once the hempcrete has been casted and cured in that area, the formwork plywood is then stripped and moved to the next section.
3. Place the hempcrete (one layer at a time)
- The freshly prepared hempcrete is placed into the wall by simply being dropped from a bucket.
4. Leveling the placed hempcrete material by hand
- An even amount needs to be dropped each time and spread out evenly (can be done with tools or by hand).
- This prepared the hempcrete for the tamping process.
5. Tamp the hempcrete around the edges of the formwork
- Hempcrete is tamped around the edges to settle it into place.
- It is important to place and tamp manageable amounts of hempcrete at one time, this helps to maintain quality. This is why the hempcrete is placed and tamped in layers.
6. One section at a time
Once the hempcrete has been casted into the form boarded area, the formboard can be removed to be reinstalled a little higher, until the whole wall area is complete.
(C) Timber Studs
- This accounts for the structural part of the wall.
- Structural Lumbar is used for: Columns, Studs, Beams, Etc.
(D) Lime Render
- This is the same as lime plaster, except it can be used more specifically for outdoor applications.
- Render means “a first coat of plaster applied to a surface”.
