Straw Light Clay Insulating Block Experiment

Experimenting with Straw Light Clay block type insulation.

Block Form Size: 20cm x 30cm x 60cm (7.9” x 11.8’ x 23.6’) dimensions based off of Rebecca Norman’s tread information.

First attempt was made with dried rice straw, cut to 15cm lengths, then mixed with a clay slip (made from sieved location based clay soil)

Drying now for 3 days on bench of our Rocket Mass Heater.

Holding shape and square edges, but extremely heavy.

Any advice on mix design that will lighten the overall weight, improve the insulation value and durability?

Mix is now only clay slip.

1. Should I process clay down to pure clay to eliminate any and all sand and silt in the slip?

2. Should I switch to slaked lime as a binder, similar to Hempcrete?

3. Could sifted hard wood fire ash help in the mix, as a pozzolanic stabilization amendment for either lime or clay slip?

Any and all advice or insight is welcome.

Cheers, Peter Martin⛰🧱⛰

P.S. There are still very few resources/materials on the subject, available on the Internet as far as I can find.

What does you block weigh now?
Has it any strength now.
3 days is not long for something that big to dry completely

Hey John,

Thanks for getting back to me. I don’t have a scale on hand, so I can’t say for sure, but the weight feels about the same as a bag of cement right now. Do understand that it’s far from dry, but in the present state it seems to be holding its shape and has the consistency of an oversized Wheaties biscuit.

May try making some smaller molds that will dry faster, to see how different mix designs work.

Any insight would be much appreciated.

Cheers, Peter📦

Peter Sedgwick wrote:

May try making some smaller molds that will dry faster, to see how different mix designs work.

I think that's a great idea.  The brick still looks very wet.

I'm following this with interest.  Thanks for posting it.

Hi Peter,   This winter I made a test block about 3'x2'x3" from Light Straw Clay. Both locally sourced reeds and clay.  It too was extremely heavy so I kind of wonder at the "Light" part of the name!
When it did finally dry though (about 3 weeks later) it did get somewhat lighter.
However, if you've ever slung bales of hay around you know they are anything but light. Maybe 40-50 pounds per bundle so even without the clay or other things mixed in, its always going to be pretty heavy.
To speed drying time, I would suggest making your mold much thinner in diameter to increase the surface area per block thereby reducing the drying time considerably.
At some point in time, it would be interesting if you could cut your block in half and see how wet it still is inside.

The sand and silt are not acting in any way as a binder so removing as much as you can would help reduce weight. The extra processing time may not be worth the effort though for the little it may contribute to the overall weight savings.

That would be a cool experiment to try using lime just for science, but because even homemade lime is much more labour and fuel intensive than processing local clay, it also may not be worth it and instead save it instead for a plaster coat where it could be more beneficial. Just guessing here though.

Love to hear about all your findings.  

Thanks folks for the responses.

I will make some smaller test molds.

In an article by Michael G Smith he states that lime degrades the straw over time, however I believe that statement may be out of date as lime is the key binding agent in Hempcrete.

I’ve also found another small amount of information about the Argentinian builderJorge Belanko and his light straw clay blocks. Here’s an excerpt from a book he cited in.

https://books.google.co.jp/books?id=4s73AgAAQBAJ&pg=PT259&lpg=PT259&dq=Jorge+Belanko+straw+blocks&source=bl&ots=KeBH1IrifJ&sig=ACfU3U0YT6gA6yYB3sF1QzOLzpejPdh1Ew&hl=en&sa=X&ved=2ahUKEwiy1Oj5_8_pAhUPEqYKHX3QA88Q6AEwCnoECAcQAQ#v=onepage&q=Jorge%20Belanko%20straw%20blocks&f=false

My intent right now is to come up with a material that fits the following criteria as closely as possible:

1. Light weight
2. Movable/stackable
3. Mold/fungus resistant
4. Fire resistant
5. Relatively high insulation value
6. Bug/critter resistant
7. Made with locally sourced free materials
8. Easy to make in large amounts

* Don’t need to be loadbearing*

I know this is probably a tall order but I feel it’s worth investigating and spending time on as a solution for insulation will make future build endeavors much easier.

The first block is already showing signs of mold. Not surprised as rice stalks have bacteria spores for making natto beans in them.

Will continue to experiment update with any findings I have. Again, if anyone has anything to add or any experiences they’d like to share please feel free. I’m more than interested in any insight regarding this topic.

Cheers, Peter of Hokkaido

So I took your advice Gerry and made a smaller mold form to test LSC mix designs.

Here are some images of what I have to date. All of the mixes seem to work pretty well.

I have also spent a few days learning to process soil down to pure clay. After a bit of research and some trial and error I have come to what seems to be a pretty good process.

It does take some time, but I’ve tried to take the actual physical processing time down to as little as possible. Using gravity and evaporation and getting decent results.

First I fill a bucket which soil, preferably as dry as possible. The dryer the better because it’s much easier to slake soil it’s moisture deficient. I’ve come to the conclusion that more water is better. More water allows you to quickly process heavy rocks and debris out of the mix with your hands and also pouring through a larger screen is much easier than a thicker mix.
More water allows you to quickly process the heavy rocks and debris out of the mix with your hands and also pouring through a larger screen is much easier and a thicker mix.

Then process it through a series of three screens one large one medium and one small. I change to the next screen as soon as the previous screen stops being affective and no longer is small enough to catch debris.

I’m processing for the intent of making clay but at the same time all the debris goes in separate piles because I feel like you can use that for different applications throughout the building process. On the smallest screen you get down to almost sand, that I put in a bucket which will become useful later on for plastering and earthen  floor applications.

Once I have a bucket what looks like pretty much chocolate milk with very little sand debris in it I let it sit overnight. Then in the morning once all of the clay has settled you end up with a layer of water on top from there I just take a short hose and siphon off the top layer of water, leaving only the chocolate milk. Then pour everything into a dollar store pillowcase and hang it in a tree for a day or so. It really depends on your soil but here I’m able to process one bucket that comes out to just over a quarter of a bucket pure clay.

Probably don’t need to process down to earth and we are pottery clay as I am now, but I figure going to the extreme and learning how to be efficient at processing will be useful in any situation. You can alway dial it back and adjust according to situational needs.

That’s The process in a nutshell. Of course there’s 100 ways to skin a cat, but I thought I’d share what I found and hopefully some of this will help others.

Here are some images of our process.
Feel free to ask questions or comments.

I’ll share the details of my block building experience in another post.

Keep dreaming, keep building...

Peter & Mimi🌈✊🏾🌈

P.S.- These soft rubber buckets seem to work great for small scale projects as they fold, making pouring easy and you don’t beat up your shins if they smash into them when you’re walking.

Peter Sedgwick wrote:Thanks folks for the responses.


https://books.google.co.jp/books?id=4s73AgAAQBAJ&pg=PT259&lpg=PT259&dq=Jorge+Belanko+straw+blocks&source=bl&ots=KeBH1IrifJ&sig=ACfU3U0YT6gA6yYB3sF1QzOLzpejPdh1Ew&hl=en&sa=X&ved=2ahUKEwiy1Oj5_8_pAhUPEqYKHX3QA88Q6AEwCnoECAcQAQ#v=onepage&q=Jorge%20Belanko%20straw%20blocks&f=false

From the link:



Question: How to reduce weight by adding a void inside the block?

Here’s my smaller mold and some test blocks. All holding together. I’ve used mixes of:

1. Just clay
2. Clay and fire ash
3. Clay and 15% lime putty
4. Clay, fire ash and 15% lime putty
5. Clay, fire ash, wheat paste

Demolding them in about 1 to 2 hours after casting. Seems best to T mold when the suns out to promote immediate trying to prevent them from expanding too much.

I’ve also scaled the thickness and the length of the straw down to accommodate the smaller size in most cases. This seems to help the blocks hold their shape. I also advise Filling the mold all in one go, making sure that all the straw is well tangled from the bottom to the top to promote a unified structure block formation.

I’ve added a top to the mold to help compress the blocks evenly across the entire surface area. After filling the blog form once and compressing a bit I flip the mold over and press from the other side. This also allows you to check the fill on the opposite side. This works well in small scale. Not sure if it will be more difficult to keep together in a large mold format. Will experiment later.

Will also update with more details of my findings as things progress.

Cheers, Peter

I have been in the business of making pressed earth blocks machines since 1972!
I found earth blocks 12 inches x 10 inches x 4 inches high was a reasonable compromise between the number of bricks and your ability to move them.
I think you are putting far more time into creating the soil for straw blocks when maybe you should make earth blocks.
They will meet all your criteria.

You spoke of lime, straw and hemp. Remember hemp is different from straw and that maybe why lime does not ruin the straw.

Strawbale can be fireproofed with a clay plaster covering.

Another alternative may be rammed earth.

Fly Ash has its own problems, I think in your case dust caused as you are working may effect your lungs.
Here is a few comments about the material
Fly ash, benefits and disadvantages

If mushroom mycelium can apply solidity, perhaps a block can be both bigger and lighter by removing the clay.

Hey John!

Thanks very much for the response. Yes I believe you are right in saying I’m spending to much time process soil into clay. It was really an experiment done based on a previous comment. I wanted to see how quickly I could do it. Also by processing my soil through mesh it gave me a chance to spend sometime really examining what is in my soil. The wet process for me was much more telling than just pushing dry dirt through a screen.

I started this thread with the intention to build insulating LSC blocks that we could stack inside our old farm house, as it is very poorly insulated at present. Since then it has become clear to us that we may be better off just building a small 4m x 5m building, double studded with LSC wall fill.

We don’t have access to straw bails here, locally, in Hokkaido Japan. They only offer really large rolls or I can get limited amounts for loose rice straw around harvest season.

So, for the time being, the blocks are not likely to be used for any wall applications in our situation. However, there is still a possibility of using some form of blocks to insulate the roof of our newly planned building.

The size dimensions you suggested sound like a good idea and you obviously know what you are taking about with that kind of experience behind you.

I’m only using the ash from my RMH, not Fly Ash, created from burning coal. It’s in small amount and not much dust as I add it to the wet mix of the clay slurry.

Think LSC should give us decent insulation , for our needs, as we will be using a RMH for heating and the space is relatively small.

Thanks again, always learning...

Peter🌾🧱🌾

P.S.- think I may have seen your block machine in another thread before. Very cool stuff.

Burl Smith wrote:If mushroom mycelium can apply solidity, perhaps a block can be both bigger and lighter by removing the clay.

Hey Burl,

Anything is possible.

Paul Stamets talks about this sort of stuff with amadou mushrooms being used to make hats. Also a few other people making lampshades and other products with mycelium based materials.

I’m intrigued.

If you’ve got the time, go for it. Would love to hear.

Peter⛰🌾⛰

Think outside the box, because the box doesn’t exist...🙏🏽

hello, i like and admire the experimentation, i am involved with a miscanthus grass and lime binder build projects , its only a hobby and something i do when time and money are spare , i have read that this type of grass is used in Japan for thatching --might be another source of a straw type product for your build , my own reading up on bio -cretes  found several studies done around the world by credited sources .A swedish university compared hemp , miscanthus, coir, rice hull husk ,and several grain stem straws, all were found suitable for this type of crete making .I think what you are making at the moment is more of a cob mix , and perhaps not as suited to produce a brick or block very easy unless you ram it /compress it ---could you just mix it up cob style and pour or tip it into a shuttering --and layer build up internal walls. I have trialed a few small batch mixes myself of hydrated lime ,clay and wood ash--it does set up and could be usable ---but the clay had to be dry and a very fine powder---not easy to source around my way and not cheap to buy and truck in , digging fresh clay and running it into the mixer with water to make a slurry then adding in the others dry worked okay as well . But i dont have enough of it on my own land in a reasonably pure quality  ,the labour and lengthy process to wash out the pebbles and soil for the quantity i need also  , meant going another way . The other limitation was trying to save up enough wood ash in the volume i need ,even though i burn turf and timber for heating and water everyday i would have to wait a week at a time for just one 200 liter mix, my nearest neighbours ---although we are rural and they all farm---are modernised with central heating oil fired .I mix up 800 to 1000 liters of mix in 200 liter batches a time in a couple of hours ,poured tipped out into shuttering ---using those plastic tubs . Which are a big disappointment for me -- sure they are great as long as the handles dont tear off ---my rate of attrition is one tub every 2 to 3000 liters of mix ---i try to get my helpers to only half full a tub and carry 2 of them---but they always land up going for a full tub .once a small tear develops next two or three loads and its a lost easy to carry tub . Looking at the formula --they are LDPE and not HDPE---i am going to experiment on a solution for these as well, cheers for now

with all that , i forgot to to mention reading about a Japanese method of a hemp,lime and seaweed glue as a binder mostly as a plastering mix i think but might be another step forwards,cheers for now

Peter- first, thank you for doing these experiments, I am highly interested din the results.

I like your separating method, it seems pretty efficient. I have done it small scale by filling a bucket 1/3 with soil, 1/3 water, then rolling the bucket or shake it or stir with a stick until the water is muddy, then pour off into another bucket, and repeat until the soil is mostly clear. I was trying to isolate sand, not silt/clay though.

I am wondering with your soil settling overnight if you are getting much clay, or if you have mostly silt?

If you take a handful of the clay-goop and roll it into a ball, hold it in the palm of your hand then smack the side of your hand with the other hand, does water come to the surface? (This would indicate it's mostly silt)

If you dry the goop a bit, then roll it in your hands, can you get a pencil width snake without cracking? That would indicate a high clay content.

i'm not sure i would recommend it, i prefer the more organic stuffs you are already experimenting with, but some thoughts - one of the benefits of STYROCRETE ( made with free recycled styrofoam ground up) is that it's extremely lightweight. generally though styrocrete is more a cement/ concrete  mix with styrofoam.

another thing you might consider experimenting with - manure.
lime may be better utilized in the mortar matrix around each block to put them together or as an outer layer.

now i dont understand it well enough to explain it, but as i understand it, with hempcrete the lime reacts to something very specific in the hemp, which i do not think is present in most forms of straw.

i agree with above posters that say you will get something stronger and better by compressing it.
when light clay straw is used as an infill wall, it is done by slip form, with a necessary step being compressing the "slipstraw" down into your (moveable) form.

Thanks for all the comments and insight.
The mix we’re using is about 90% rice straw, so I’m pretty sure they would be categorized as LSC. Here is a look at them up close.

I also just did a water test and the float, so that would lead me to believe that they have a fairly good insulation value.

It’s likely that there is some silt still in the processed clay for sure. However we live at the bottom of a valley.All of the local farmers complain about the “clay soil”. When I dig into the earth I get stuff that peels out like scoops of hard ice cream. Pretty sure silt won’t do that. I’m also pretty sure I could make earthen wear pottery out of the processed stuff. I took pottery classes in school and it seems to me to be very similar inconsistency to what I used then.

I have looked into using the seaweed glue but that requires me to buy more materials which I would like to avoid. Use what I have available as much as possible.

Peter

Hey Leila

Didn’t see you comments before posting the last one. Probably want to use as little styrofoam as possible.
Thanks for the point on the lime as well.

We are planning to use the slip form infill process for wall cavities. At present the block experiment was really just for me to get a better understanding of the materials and how they held together. Most likely going to use blocks in some fashion when insulating the roofing area of a new small building.

Cheers Peter✌️

yes, i have only done small experiments, making paving stones for walkways, with styrocrete.

it's actually also a drag to process the styrofoam, though it is a free easily obtainable material, does have very lightweight and insulation properties, and the idea intrigues me theoretically =)

but some ideas anyway.

i think the idea is good, i think it can work ok, if you were to make a bunch to mortar them into a wall.

as far as stacking them that's a good idea too, and then they are not permanent. as infill, and not load bearing, light clay straw works well, but with the bricks you may be able to make load bearing walls, where most of the stregnth would actually come from the mortar matrix, which is quite strong. so the blocks would be like mini in fill, inside the load bearing wall supported by the mortar matrix between the bricks.

Peter, I have spent time experimenting the way you have.
If we dont we have less knowledge about what we are doing.
Have you thought of making wall panels on the ground, lined on one side with plywood and then filled with you mixture.
When it dries you can stand the panel up and install it into your wall structure.
If you plan it correctly you could eliminate additional timber wall studs by using the panels as a structural item.
You may see the term, SIP- structural insulated panel.

When building, if you can get a roof up with minimal effort you will have a good area to work under and store items out of the weather.

Thanks John,

I had a look SIP. That might be one way to do the ceiling panels. I’ve got lots of timber to work with so extra studs are not an issue and can alway use for wall fastenings and shelving etc. This tiny house project was pretty last minute and we are trying to do with as much salvaged materials as we can. Maybe even use some trees from our property in round timber format.

Have another tread started under the tiny house category if you’re interested. Gonna start digging my first foundation ever tomorrow by hand. Should be interesting...

Thanks again for the feed back.

If we don’t try we don’t learn...

Cheers, Peter

This thread is now a bit older, but would be curios to hear about any progress - what are your conclusion of the different mixes? Are the last batches of blocks lighter?

Also on the topic I can recommend the book "Light Earth Building: A Handbook for Building with Wood and Earth" by Franz Volhard. It is the main book on LSC in the german speaking area and talks about different types of loam/earth and pure clay one  can use as well as how to get to different densities and insulation values for both blocks and the wet fill method. I have not read the whole book yet, but from what I can see he talks of at least 200-300kg/m3 for mixes that use loam/earth very high in clay or possibly pure clay and for more normal earth/loam mixes (i.e. less clay) at least 600kg/m3. So these values should give you good indicators of what weight to expect of your blocks dependent on the density. Also he does not recommend adding lime to the mix but he can recommend using urine (best from the horse) instead of water for mixing the clay slip.

Thanks for the info!

To be honest I’ve kind of abandoned the experiment. In the end I could seem to find any reason to use this as a form of insulation in our present situation. Did learn a bunch about the binding properties of clay however. In the long run, lime may not be a good additive, but it was one of the only samples that did not exhibit any signs of mold during the drying process.
Adding wheat paste was not a good idea.

Thanks for showing interest and best of luck in all your endeavors.

Cheers, Peter

No worries - just for sake of completeness, I read now that lime for LSC mixes with very high clay should be ok and can help with reducing cracks. It was more in mixes with lower clay where lime might be unhelpful. And another addition he can recommend is very small amounts of sodium carbonate (Na2CO3) or tannins as that way one can reduce the amount of water up to 50% and therefore reduce the drying time of the mix.

Again, you might not be needing this information anymore, but might be useful for others or you might still find it interesting: I saw now in your tiny house thread that you talked about LSC underneath the floor and potential issues. I don't have any practical experience but in The Light Earth Building book there is a small section on floors and it does talk about using LSC or LSC blocks as part of the underfloor when using a wooden or tile floor. The cob builders handbook also talks about LSC optionally underneath an earthen floor (above a base layer) and that it is important to dampen down/compress an initial layer of 3-4 inches to 1 inch.

Also thanks for sharing all the progress you made, it has been very interesting to read.

I'm inspired by your experiment to get back into the world of light clay. I've done some building in light earth and found that not compressing it still produces a very strong wall, but much lighter and with better insulation. Of course there is a sweet spot which will depend on the earth, the type of straw and the insulation/ thermal mass properties desired, but I would suggest doing more experiments to see how loosely you can pack the blocks and how lightly you can coat the straw with clay slip without losing too much strength. I've been thinking of doing these experiments myself after watching a friend make hempcrete blocks.

Hi guys,

Do you think these LSC Blocks can be used to make Masonry wood burner stove, the ones like Matt Walker's designs?

Thank you,

Hi Tuananh,
I don’t think the blocks can be used for any wood burning device.
They are light and insulating, also potentially flammable or at least damaged by high heat.

The part of the masonry heater where the wood burning happens, also called the core, needs insulation, but at very high temperature. Firebrick or fiber board is usually used there. Straw bricks would burn out and deteriorate quickly. Even normal brick can not handle the heat very long.

The heat storage part needs heavy conductive material, the opposite of these bricks. Normal brick is good here. Also cob, stone, concrete.