My alternative to hempcrete:stinging nettlecrete

Made this a few years ago but sadly couldn't finish it due to moving. I can't restart the idea at moment due to not having the land I had before so though I would share it with people on permies for people to try out.

Using the same principles as hemp crete I was using nettles as they were freely available, perenial and easy and legal to grow. Nettles are also very closely related to hemp and have lots of silica (the stinging part) which helps explain the strength. Initially I made a small test piece in a terracotta pot once it had dried and the terracotta removed it was possble for it to suport my weight.

Harvest the nettles
Dry the nettles and bash off the leaves.
Run the nettle stems through a mulching machine chopping them up
Mix the nettles with hydrated lime and press into blocks. I used a washing up bowl for this.
Let the hydrated lime dry and then remove the blocks

The plan after this was to create an entire wall and lime plaster this. I started this as I went along but then had to move. Obviosuly like hempcrete you will need to protect the blocks from being satured (with a roof and waterproof foundation) or they will fall apart. However they did last while I was at the property.

More pictures that didnt upload last time...

I had no idea one could do something like this. Makes me wonder if horsetails could be made into a 'crete. How's your nettlecrete holding up?

Years ago i was making a nesting spot for swalliws which live in my barn. Some kids of a friend where passing by and i decided to use nettle fibre. I removed the leaves and carefully banged the green fleshy cells off on a wooden board with a rubber hammer. The fibres i washed and snipped into usable bits.
That i mixed with sand and cement and shapedit in the size of a used nest on a wooden board with screws sticking through.
The kids liked to help except with the nettles. And the swallows love there new houses. They lined them with soft material.
Should have used lime, but i had some leftover cement.

Nicole Alderman wrote:I had no idea one could do something like this. Makes me wonder if horsetails could be made into a 'crete. How's your nettlecrete holding up?

I've wondered the same about horsetails. They are rampant in the low areas down by our local river.

A couple of other plants to consider would be flax, an annual but easily cultivated and seed is widely available, and hemp dogbane (Apocynum cannabinum) a perennial common here in the great plains and also easily cultivated. I just happen to have a cup full of dogbane seedpods sitting on top of my dresser.

Nicole Alderman wrote:I had no idea one could do something like this. Makes me wonder if horsetails could be made into a 'crete. How's your nettlecrete holding up?

Sadly I have no idea as I had to move to another part of the country. Where I have moved to initially had no nettles! Now after improving the soil have they only just started to arrive, the previous place was a chicken farm and then a sheep pasture so it shows me they really are an indicator plant. Sadly I dont have the space to grow lots of nettles now so apart from a small test block I doubt I can make a structure again.

If anyone wants to explore this idea more some interesting things to consider might be:

The chemistry of the plant before and after flowering as the nettles should be more saliceous after flowering.
Land area needed for a nettle block. I think it was a few square meters.
Inclusion of leaves perhaps it doesnt have as much tensile strength but does it matter?

Also I always thought it would be interesting to take a 'turf' of nettles to a site roll it out and grow the nettles harvest them and process them onsite for the building there. However its probably not too practical.

My guess is horsetail would work but it might be less strong than nettle. Why not give it a go? When they do hempcrete they dont use it for load bearing walls so the horsetail crete could well have some applications.

I think really any chopped up organic will work, just like straw in ancient sun-baked brick.

I always though of hempcrete as a bit of a silly idea, in that it's just the latest in a tradition of organic fibrous matter added to hold clay and sand mixtures together. You can use almost anything that will process down to the same basic parameters, including animal fibres, and while the mechanical properties will vary based on size and composition of the individual fibres, they will have the same basic strengths and weaknesses.

Most of the difference will come from specific mineral ratios and the method used to press the bricks. A product with truly superior mechanical properties will be pressed like Compressed Earth Block or rammed earth. Someone please correct me if I am wrong, but the fibrous additions are there to improve tensile strength and elasticity, and to help the bricks or masses dry out evenly on the inside, right?

I would be interested to see what differences could be found in bricks using the same mineral ratios, in the same block press, but using different natural fibres processed to the same fineness. I would bet that we would find a number of applications in which hemp might be superior, but perhaps the fibre length would make it unsuitable for smaller sizes, and perhaps the animal hairs or the milkweed down would have other surprising benefits, like perhaps in durable but thin applications like tiles.

Just spitballing here. But you should be able to use whatever is at hand that is processable down to the size and fineness required.

-CK