Humus Insulation Blocks Fire Test

Previously, Meadow had an idea to use what-would-be-wasted humus to see if it’s “fluffy” properties could be utilized for making blocks for insulation. The first thing she did was make a clay slip to make clay, and then she used the humus to make a “humus slip” in a similar fashion.

Pulling out the fluff was easy, but she mixed it with different materials, like straw, lime, and/or paper (TP (toilet paper) or egg cartons), molded them into 6″x6″ blocks, and sun-dried them in a make-shift solar oven till dry. This was in 2022. Now it is 2023, and she found time to buy a propane torch to do a simple 60-second fire test on each block.

But we are getting ahead of ourselves here… first, she had to make the blocks! Here is how she mixed the materials for each of the different blocks.

Fire Test

Next was the fire test… not anything serious, but enough to get a feel for which versions of these humus blocks might have qualities such as strength (so check for brittleness), insulation value (if heat passes through to the bottom of the block), whether they burn easily (red glow intensity) or give off smoke, discolour/char, or flake off easily once burnt. So Meadow chose this method for scoring the test samples in the fire test, shown below.

The Scoring System

0 = best/no change
1 = barely/at end
2 = medium/mid-way
3 = worst/at beginning

Results of Fire Test with Propane Torch

Below is the chart for the fire test on each of the blocks (see chart above). Meadow wanted to compare different mixtures to see which properties might be better than others. The burn time was 60 seconds per block (preferably in the middle of the block, away from breaks/cracks), with the torch being held 1 cm above the bricks.

Results & Conclusions

According to the chart above, the results show that “fluffy” humus by itself was very brittle and so broke easily–not a great material by itself for making blocks of insulation. However, adding straw as fiber (such as in adobe mud blocks or clay cob) did make the blocks stronger, but also had its own set of drawbacks, such as glowed red from the fire, causing excess burning and smoke, more char/discolouration, and a weaker block after being burnt (flaked off easily).

Based on the above results, it can be generally said that:

• humus, although “fluffy”, is not strong enough as an insulating material (by itself)
• adding straw makes it stronger, but has so many drawbacks that it may be best to avoid it as a binder in something that could potentially burn (such as a house fire)
• lime has anti-bug properties, but otherwise may not be a great addition (more cracking occured)
• paper, which was a 50/50 mixture of recycled paper from egg cartons (torn into tiny bits) and toilet paper (TP), which together gave tremendous properties to the humus insulation blocks, mostly in low ignition, less smoke and char, more strength (less brittle), and higher insulation value

Recommendations

Here are some recommendations for any future humus (or other earth/soil-and-paper-based) test blocks…

Straw did add some tensil strength to the humus blocks, but better options may be investigated, such as:

• spun glass/fiberglass (made from sand/soda/lime–an insulating material that does not burn), but has high embodied energy, costs money or requires special equipment to make, and is not found readily in nature
• Rockwool (spun basalt rock and recycled slag) fibers could be pulled apart and added to the humus mix quite easily, but it carries more embodied energy, must be purchased, and is not found naturally
• Merino wool/other wool could be used as a fibre binding agent, is naturally fire retardant–does not ignite until 570-600 C (1058-1112 F) (source)–does not melt or release toxic fumes, is all natural, and a renewable resource

Although other materials are available that do not burn, such as metal, stone, concrete/cement, or gypsum products, these make insulation heavy, may increase thermal mass (metal/stone/cement/concrete are conductors, not insulators), and may or may not aid as a binding agent (including gypsum, even though it has some limited insulation value… it can be a binder, but adds no real strength). Clay products (perhaps clay-fired items) could be less burnable, but unless the entire insulation brick (or panel as the case may be) were fired, it would likely not add strength.

Last Thoughts

One key factor in creating insulation, or insulation value, is not just its thickness, but also how porous it is–the tinier the locked-in bubbles of air, and the more of them, the better insulation value it will have. The “fluffy” aspect of humus seemed, at first, to be a possible natural and earth-based material that could be put to use for this purpose (if it were otherwise going to be wasted due to excavation sites and construction purposes, etc., rather than used in a garden); however, humus would still need to be tested, and nothing of this sort (in Meadow’s opinion) should ever be manufactured, but rather be a local site-based product that is homemade by the landowner(s). Humus has too many amazing properties to be quarried out and placed on the market. Too much environmental disaster has already occurred on this planet because of mass manufacturing, commercial use and consumerism.

With that said, Meadow is wanting to continue her research on making alternative insulation panels that can be made on-site, and as free as possible, and with natural materials that are eco-friendly. All of this started because of needing a clay slip, and discovering humus was “fluffy” and might be a good insulation material.

Next on her agenda is to take the E4 style block and exchange the straw out for other fibres (wool, spun glass, and rockwool) to test and compare them. E4 block is composed of humus, straw, and paper; however, the new versions will have new identifiers. Other versions using regular soil, rather than humus, may also be considered.

Choices for possible future experimentation:

F1: 50% humus with 50% fiberglass/paper mix
F2: 50% humus with 50% rockwool/paper mix
F3: 50% humus with 50% wool/paper mix
G1: 50% soil with 50% fiberglass/paper mix
G2: 50% soil with 50% rockwool/paper mix
G3: 50% soil with 50% wool/paper mix

Or, the above ratios may change. Some comparisons to different recipes of fidobe may need to be researched first to find the most insulating version, which is still fire resistant and strong. Can they be fired in a kiln? This would mean more clay rather than soil or humus. Lots to think about!

Keep watch in the future for more experimentation…