Hempcrete FAQ
What is hempcrete?
Hempcrete is made from industrial hemp hurds (core), a lime binder, and water.
How many cubic feet of hempcrete can I make with one bag of hemp hurds?
You can produce approximately 4.5 cubic feet of hempcrete material. Hemp hurds will need to be mixed with a lime binder. One example is TransMineral USA’s Batichanvre.*
Should I take any protective measures when using hempcrete?
Protective goggles, gloves, and masks should be worn when mixing hempcrete, because hydrated lime is caustic.
Can I use hempcrete in the foundation of my building like concrete?
No, hempcrete cannot be used as the foundation for a structure, because the mixture can biodegrade if exposed to excessive moisture for long periods of time.
How does hempcrete effect my foundation?
Although hempcrete cannot be used in foundations, hempcrete can be lighter than concrete. A more lightweight foundation can be poured, so long as it is in accordance with your local building codes and engineer’s instruction.
If moisture poses a problem if hempcrete were used in foundations, then what prevents rain from penetrating my house?
An exterior hemp plaster finish should provide the necessary protection from the rain and also add to the exterior beauty of your new healthy home, although houses have been built without a hemp plaster finish. The hemp plaster will provide an end result that looks similar to conventional stucco. Because hemp plaster contains more lime and water than the hempcrete wall mix, the plaster will further seal the structure as well.
If I use hempcrete for my walls, how does this change the materials used to construct the walls?
Hempcrete creates a monolithic structure, which acts as your OSB, insulation, and drywall. No cavity is necessary, but framing is still required.
Can hempcrete be used as a structural material?
Hempcrete is a non-structural material which is cast around a timber, steel, or concrete frame. Hempcrete will provide additional support to the frame.
Are expansion joints necessary for hempcrete?
Hempcrete does not require expansion joints, because the mechanical properties of the lime in the hempcrete mixes allows for greater flexibility.
What is the typical thickness of hempcrete for walls?
Hempcrete for walls is typically cast at 12” thick and will provide a R-value of 25, according to the British Board of Agreement, which is the UK equivalent of the ICC. A R-value of 25 for the walls of a house exceeds the North Carolina building code requirements and can also help you reduce the size of your HVAC system from the typical 5 ton unit to a 1-2 ton unit, saving you on HVAC costs.
How does the composition differ between the hempcrete wall, lightweight, plaster, and floor mixes?
The lightweight hempcrete mix will have more hemp hurds and less binder in it, while the floor mix is comparable to the wall mix. The hempcrete plaster mix will have increased levels of the lime binder in comparison to the other mixes. Depending on the climate (dry and warm vs. wet and cool), the quantity of water should be adjusted to either speed up or slow down the time it takes for the hempcrete to dry.
Subfloor hempcrete – This type of hempcrete mix is laid on top of gravel and should be moderately ventilated, if above wet ground.
Wall hempcrete – Most common type of hempcrete used and usually casted around a timber frame.
Lightweight hempcrete – Small quantity of lime binder is used to weakly join the hemp hurds togther. This type of hempcrete is suitable for use in attics and interior partition walls.
Hemp plaster – Highest concentration of lime is used for this mix out of all the hemp hurd mixes, so the plaster is workable. The lime helps fill gaps between the hemp hurds and is ideal for finishing the hempcrete wall mix, brick, or stone.
Who can cast with hempcrete?
Hempcrete is a non-structural infill material, which general contractors, DIYers, carpenters, students, etc. can learn how to use with the proper training and testing.
Does hempcrete require a permit?
Depending on the application, hempcrete may or may not require a permit for use. If you are building a small structure, you may not require a permit, but if you are building a home, then a permit is more than likely required. Hempcrete does not yet have a certification/standard from the International Code Council (ICC) or the American Society for Testing and Materials (ASTM), so local building officials must be informed on a case-by-case basis. Although hempcrete has received approval by the British Board of Agrement, this certification does not help with the permitting process in the United States of America (USA).
Can hempcrete be sprayed?
A technology has been developed where in hempcrete material can be sprayed by a hempcrete spraying machine, but caution should be taken with the type of hemp hurds used in this apparatus.
Can hempcrete make you feel “high” and is hemp safe for my children?
Hemp cannot make you feel “high”. According to Danny Gough of Energy Solutions, (WSJ HomePlace 01/12/14), in a report released by the Healthy Building Network, researchers looked into over 1,300 ingredients found in common building products and identified 38 chemicals that can cause asthma. Hempcrete is an all-natural mixture of hemp hurds, a lime binder, and water.
Source: http://www.americanhempllc.com/#!hempcrete/c1y0f