Q1. What are the materials used to make Hempcrete?
A. We grow our own Industrial Hemp in Australia for building, mixed with a lime binder which has all the hydrated and hydraulic limes included in it .
Q2. How is Hempcrete mixed?
A. Its is mixed in a 120ltr, 300ltr or 750ltr pan mixer
Q3. How is Hempcrete placed and compacted?
A. Either with temporary forms (GeoPanels) on either side of the structural frame, screwed to the frame at the thickness you are casting or with permanent interior lining board and temporary exterior shuttering (boxing).Tamping the exterior edge of the Hemp/Lime mix will add compaction to the exterior edge of the wall.
Q4. How long do you leave the temporary shutters on?
A. As soon as we have cast a section of wall we can immediately move the shutters to a new section of wall. Typically we finish casting for the day and move the shutters next morning.
Q5. How high can we cast at a time?
A. Typically we will cast in 600mm lifts but you can do as little or as much as you like, depending on manpower.
Q6. Do you need to do any testing of materials before starting the job?
A. NO – you will easily find a rhythm of mixing, casting and tamping with the work crew you have on site and ratios of hemp to binder to water are standard for all applications.
Q7. Can we build footings or pad with hemp or do we use concrete?
A. Hempcrete cannot be used below ground for foundations. Cellulose exposed to below ground dampness for extended periods will deteriorate, like any plant material, even wrapped in lime.
Q8. How long do we leave the Hemp/Lime wall to dry before plastering?
A. Depending on the time of year typically we leave the walls to dry out for 4-6 weeks before rendering At around 15% moisture content you will not get any leaching of the lignin’s from the cellulose – too wet and lignin’s may leach out thru the lime render.
Q. What precautions do we need to observe when using Hemp/Lime?
A. Lime is caustic so it’s a good idea to wear gloves when working with Hempcrete. Goggles and dust masks make for a more pleasant experience too. also long pants and shirts are and advantage from the dust covering you.
Q9. Is there any waste when working with Hemp/Lime?
A. There is always spillage when casting Hempcrete but we pick it up and re-use it in subsequent mixes so no waste.
Q10. What happens to the hemp walls if it rains?
A. Hempcrete will take on water if rain is beating against it. Depending on climate and time of year you may consider protecting the casting areas with tarp’s. That way you can keep working in inclement weather.
Q11. What finishes can we apply over HempCrete?
A. Hempcrete provides its own substrate for application of lime plasters directly without need for metal lathing. Or you may wish to use brick, wood or metal facing for aesthetics. Other than wood facings we install a breather baton so the Hempcrete can maintain air flow because metal is not permeable.
Q12. Can we use Hempcrete for bathroom walls?
A. Yes, you can use Hempcrete in a bathroom and finish with lime or clay plasters that will breathe in and regulate moisture. In Europe people have been using lime materials for ages in bathrooms without the need for extraction fans.
Q13. What finish can we give the flooring if done with hempCrete?
A. Hempcrete can be used to insulate floors over which you can apply a sub-floor and then whatever flooring material you wish. We prefer to leave a 1″ air gap between the floor joists and the subfloor to allow Hempcrete to breathe, thereby giving the best insulation value.
Q14. Can the roof be done with hemp/lime?
A. Yes, the roof can be done with Hempcrete but remember, as above, there needs to be a ” breathable air space between the top side of the Hempcrete and the underside of the roof sheeting material, presumably plywood.
Q15. Does Hempcrete require expansion joints?
A. NO expansion joints are required using Hempcrete materials, unlike cement. Even when finishing Hempcrete with lime stuccos there is no need for expansion joints as lime is very flexible and will heal itself after only a couple of months. New buildings are prone to settling and cement finishes will crack as they are brittle whereas lime will crack but reshape itself because of its crystalline shape.
Q16. Are there any special requirements when casting Hempcrete?
A. There are no special trades required to install Hempcrete walls, floors or roofs, making this material even more suited for non-skilled labor.
Q17. How big an area can we cast at once?
A. Casting into double sided temporary shutters, a 4-5 man crew can form and cast an average 5 cubic meters.
Q18. When mixing Hempcrete do you need to vibrate it like concrete?
A. NO. When mixing Hempcrete and casting you do not need to vibrate like concrete. There is no “slump” in Hempcrete as we limit the amount of water used to hydrate the lime binder.
Q19. How about framing: any special conditions?
A. Hempcrete is regarded as a non-structural, monolithic infill material, cast around the structural timber or steel frame of the structure. its must conform to australian standard building code As1684. Hempcrete will harden and in fact help to brace the structural members.
Q20. What is the mixing time of 1 cubic meter?
A. Most people use a regular mortar mixer (horizontal) in which you can mix 100 liters 10kg of hemp with the required ratios of Lime binder and water. The hemp goes in first to aerate it,then the water ,then the binder, mixed for 2 minutes until all the shiv (hurds) are covered with the lime binder.
Q21. How long has hemp been around?
A.There are projects in France now 40 years old and getting stronger by the day.
Q22. Do you have a cost per square metre of wall?
A. There are quite a few variables on cost but it compettitve with convetional materials.
Q23. How did the idea of using hemp for building come about?
A. Industrial Hemp has been on our planet for thousands of years and used in many ancient structures together with limes long before we had conventional cement. We have adopted a carbohydrate approach to building healthy homes without the need for petrochemical where possible.
Q24. How is hemp more beneficial in building compared to other materials?
A. Carbohydrate based building materials are healthier and less damaging to humans. Toxic petrochemical materials are responsible for many illnesses and increased medical bills. Hempcrete is breathable and is completely non-toxic due to all natural materials. Plus, Hemp/Lime protects the structural integrity of a home and therefore will last considerably longer than conventional construction.
Q25. Are hemp building materials cost effective?
A. Hemp/Lime materials are comparable in cost to traditional brick and block construction.
Q26. Are hemp building materials safe/healthy?
A. There is documented evidence that Hemp/Lime has contributed to more than 50% reduction in sick leave and absenteeism in Europe where they have been building with Hempcrete for +/- 30 years now.
Q27. How does hemp help cut down on energy use?
A. Because Hempcrete is super insulating the need for additional mechanical heating/cooling is reduced. For example a typical home will have 1 ton HVAC per 46.45 square metres Using Hemp/Lime for insulation will reduce that requirement to 1 ton per 140m2 (60%) That equates to another cost saving when building with Hemp/Lime.
Q28. Animal bedding: how does hemp assist in this area?
A. Hemp is a premium animal bedding and 80% of all hurd production in Europe goes into pet bedding currently. Hemp absorbs 4 x more waste than other bedding materials yet decomposes 2x faster after use. This makes hemp very good for use as a fertiliser after being used for bedding. Yes, it is more expensive than other bedding materials but reduced labor costs over time make Hemp more affordable over all, and better for your pets.