Hempcrete and Rammed Earth Crystallizing
Cynthia Bruinsma
4th year, Bachelor Interior Architecture & Furniture Design

What did you find out with this research?
Hemp is a versatile and sustainable material and can absorb CO2. Combined with lime it becomes hempcrete which has the flexibility of clay and the strength of concrete.

My research was about the crystallization of hempcrete and rammed earth and the various patterns that emerged with the addition of different household chemicals.

Materials and amounts:
For rammed earth: 5g clay, 20g earth (sourced from Friesland), 50g limestone (from Hornbach), 40ml water.

For hempcrete: 20g hemp flakes, 80g lime, 150ml water.

For crystallization: alum, ammoniac, dish soap, fabric softener and all-purpose cleaner.

Demineralized water

Your hands. For gathering the earth and sand. Also, as a tool for shaping molds and pounding rammed earth.
Machines in the wood workshop to create a mold to put rammed earth or hempcrete in. (Tip: paper is also a great mould for this material, or even fabric for a more abstract output.)

Funnel, filter paper, glass cup, electrical wire, bucket, string, toilet roll centres, cover (e.g. bottom of a soft drink bottle).

Rammed earth

  1. Start with 5g clay and 20g earth in a bucket

  2. Add 40ml water

  3. Mix with limestone


  1. Start with 20g hempcrete and 80g lime in a bucket

  2. Add 150ml water

For both

  1. Make sure your surface is flat and place your toilet roll mould on it. Then add small pieces of materials and stamp it with a tool, such as a stick

  2. Repeat until the mould is full.

  3. Let your sample dry for 2 days and carefully remove paper.

Mixtures with chemicals:

1. Heat about 200ml of demineralized water.

2. Dissolve as much alum as possible in the water; continue until it no longer dissolves and then add a minimal amount of water.

3. Filter solution into a beaker and cover it (do not seal it).

4. Let solution stand for a few days until crystals form.

5. Filter off the solution so that the crystals are separated from the solution (mother liquour).

6. Make a new solution as described above.

7. Select the largest crystal from those you had already made and attach a string around it. This will be the growth nucleus.

8. Attach that string to a batten or a piece of thick electrical wire, which you can hang over the opening of the jar with the new solution in it. Make sure the crystal hangs in the middle of the solution.

9. Place covering over it, it is important that no dust gets into the solution.

10. Wait.

11. After a sizable crystal is formed remove it from solution.

12 Pour solution into a larger pot and heat it.

13. Make a fresh warm saturated alum solution and add it to pot.

14. Place crystal back into the solution.

15. This process can be repeated if necessary, so the crystal can grow.

16. Mix a fresh warm saturated alum solution with the chemical you want to test.

Health and Safety Precautions

Use gloves if you want to mix materials that include chemical substances. Safety glasses and/or mouth masks are also useful for mixing limestone because it stirs up dust.

This recipe is part of Touching: A Research Method in Art and Design, an exhibition curated by architect and KABK tutor Laura van Santen, featuring the materials and research of students, tutors and workshop instructors from the KABK.

More information on the display, all samples and recipes can be found here.