What are the biggest disadvantages for hempcrete?

There are no disadvantages. Every part of the industrial hemp plant is used for building. Hemp can be used to make studs in walls, (replaces wood) used for cabinets, countertops wall panels, flooring, sinks, tubs, showers, etc.

It has a net zero carbon inprint.

Hemp has a fire rating of 4+ hours.

The walls breathe & allow moisture to evaporate so no mold. No offgassing. Termites avoid it like the plague. Not a source of food for bugs. The insulation value depending on the specific application (hemp batting insulation vs solid walls) is beyond current applications of spray in foam, blowin or fibreglass etc.

I would recommend to mix hemp sheeves with magnesium oxide as a binding agent which is preferred over lime. Lime is good too but the magnesium oxide is my personal preference.

Hi,

I have published review papers on hemp concrete titled, “A Review of the Properties of Hemp Concrete for Green Building Applications” & “Hemp concrete: carbon-negative construction”.

The main disadvantages of hemp concrete are:

1. Not enough research has taken place on hemp concrete yet. Lack of complete understanding of material science.
2. Currently, hemp concrete is used as a non load bearing building component/ in-fill material
3. Mechanical properties are not in the desired range – low compressive strength, flexural strength, etc.
4. Only one method of construction – timber frame structure, has been scientifically validated.
5. Manufacturing processes are not standardised, thereby leading to an unstandardised product – safe only for non-structural purposes.
6. Lime based construction is tricky and requires a certain amount of training to be imparted to personnel.
7. Early age mechanical durability issues are rampant.
8. Because hempcrete walls are thicker, we risk losing carpet area. (contributed by Tommy Gibbons, original response in comment below)
9. Commercially available binders are rather expensive. Offsets the cost savings (if any) from using hemp.
10. Hempcrete might not be best suited for all climatic conditions. For example, in hot and humid regions, like south of France or coastal India, the increased uptake of moisture could induce super heating inside the building. Therefore, it is important to design the ventilation well. Other remedies could be rendering the exterior surface of the hempcrete wall, and adding a plaster of lighter colour, preferably lime.

Currently, this is all I can think of. I shall update the list as and when I can come up with a few more demerits.

Currently, because of the legal grey area in a lot of countries, another huge disadvantage of both hemp concrete and hemp CBD oil, is that a lot of the products sold are not high quality. This is because, thanks again to laws, there is a huge lack of quality control. This is a real shame, especially for something like CBD oil, because people take it and expect it to help, but the oil isn’t high enough quality to actually help with their symptoms, and then they’re put off it for life.

Aside from a few small disadvantages, however, hempconcrete or hemp concrete, is likely going to be a huge scientific advancement (depending on what the research actually shows) and as it’s a carbon neutral or even carbon negative construction technique, it could replace timber in the future. Especially considering how long a hemp plant takes to grow, when compared with a tree.

Disadvantages of hempcrete:

• Hemp concrete cannot be used underground or underwater applications.
• The cost of building with hempcrete is a little expensive in comparison to the other conventional methods.
• Hemp is not as always readily available as traditionally building materials like concrete in most countries and it is declared illegal in a few countries as well.
• Hempcrete is used only with timber framed structure.
• The hempcrete walls are thicker and it given less carpet area.
• The mechanical properties of the hempcrete are not desirable for a heavily loaded building.

For more details on hempcrete, you may refer to the following article:

Hempcrete as a Building Material: Pros & Cons | Properties | Applications