How to make small scale hempcrete?

I was watching this video about hempcrete.


It is supposed to be just made of lime, shredded hemp stalk (which you can replace with straw if not available) and water. There is also briefly mentioned a lime heating process, but nothing more detailed than that.

I'm not into making a house with this, but I would be interested in making things like plant pots, small tables and stools, and various artwork with it.

I need more info though. Like...
Is there a specific kind, or prepared lime I need to use?
What is this heating process you need to do to it?
What parts lime to hemp/straw is recommended?
How long is the curing process?

It seems like you could make some neat things out of this, but I haven't found anyone doing so. Are there any experts that could offer advice about this kind of thing?


There are several variations of this mix possible, as Kiteman pointed out using ready to go concrete is the easiest way.

But in other areas of the worls just water is used, when it freezes the added fibres even make the stuff shatter and bullet proof.

A friend of my in Europe had experimented with alterative building materials for many years, so I will try to list what I still remember from his work:
You can use all sorts of "filling material" from dried grass, over long straw to tyres and polysterene foam bubbles.

Polystyrene makes a very light weight concrete with uperior insulation properties.

Compared to a normal block of concrete you can save up to 40% weight.

Instead of concrete old mixtures based on hydrated lime, clay or even mud can be used, he experimented at one stage even with resin from pine trees as a binding material.

The key to success is preperation, the ingredients must be dry (no moist plant material) and fibres should not be longer than 15cm unless you are using moulds where you can compress the concrete properly before it sets.

If the fibres are too long you will have the problem that they lump together causing a mix concrete with a massive ball of (censored) floating in it.

Modern technology is really good and a concrete mixer would be the obvious choice for the mixing job, but my friend actually prefers a big tarp on the ground plus a concrete mixer.

Concrete and sand (or clay, mud) are prepared in the mixer, the filling material is spread over the tarp.

Add the ready concrete ( a bit wetter than what you would normally use for making concrete jobs) and spread it over the filling material.

Now you work the mix with 2 or more people by lifting the tarp on the sides and edges, literally rolling the mix from one place to the other.

The mix is ready when it is evenly mixed and the concrete gets back to a normal consistency - at this stage the plant material has partially absorbed the water from the concrete causing a really good bond after curing.

You can check the quality of the mix by breaking it with a hammer, it should not seperate around the fibres but with them.

Key for outdoor use is to make it waterproof, so the foundations should be normal standard concrete and the outside surfaces should be painted or covered with some rendering material.

If the natural look should be kept get waterproofing additives to mix directly into the concrete and seal the outside with lisnseed oil or similar - be aware that natural coatings need to be re-applied every few years or when there is the need for it, like on the weather side of a wall.

Kiteman2 years ago

I'd be inclined to just mix ordinary concrete, using cement powder, but replace the sand & gravel with your fibres.

Curing times will vary, depending on the thickness you make, but plan on anything from "a few hours" to a full day for plant-pot thicknesses.