Mystery result when extracting clay from soil

[RedShirtGuy]

I'm having a fiddle around with the earth on my bush block (between Clunes and Maryborough) with the long term intention/hope of making mud bricks for a house. At the moment though I'm just experimenting with samples from different locations and trying to extract just the clay to have a play with.

A professional soil test says the ground is a silty clay and I have been able to successfully process some reasonably nice clay from some undisturbed locations that haven't been deep ripped by the previous owners -- those test sites were total failures.

These problem samples though have come from the bottom of two different dry dams and from between 1 inches and 2 feet deep. They've been sifted/crushed/soaked/slaked and all the unwanted muck, shale and grit removed which, when wet, is leaving me with mud that's smooth to rub between the finger tips.

Similar to a basic jar test, when it's all shaken up in a bottle with additional water and the contents are fully in suspension then left to settle, the water never goes clear again - even after a week or more. This says to me that there's little to no clay present. BUT what does settle in the bottom of the bottle, after only a couple of minutes (and doesn't change much if left longer) is a smooth, shiny and very sticky mud that I can lightly roll into a thick sausage or ball which will air dry hard, but brittle. If I pour a thin layer of a sloppy mix of it onto cement sheet it dries quickly and crumbles into a fine powder.

So...if it's not clay...what the heck is it and why is it behaving so much like clay, but not as usable?

[Skew ChiDAMN!!]

Really fine silicates perhaps? Any 'sparkle' to it once it's dry, if you get up close 'n personal with a magnifying glass?

(Most anything will feel/roll like clay if ground fine enough and given a suitable lubricant.)

[elver]

Sounds like silt to me. Is it dilatant? Make a patty in your palm , tap the side of your palm with your other hand, if water rises to the surface its probably silt. The suspended material in the jar is clay.

Did the "soil tester" do an atterburg limits test or just a visual assessment? (most only do visual but tell you the did a "test"). If they did an atterberg plotting on the A Line chart will tell you what it is and how plastic it might be.

[RedShirtGuy]

Rightio...it is dilatant so I'll say it's silt too.

Reading back over the test report, the core samples revealed highly weathered siltstone at a depth of 600mm plus. Given that the dam bottoms I took these samples from are deeper than that, I'd reckon it's safe to say that that is what I was digging in...even if it was relatively easy digging in places (and definitely not easy is others).

So obvious, yet it escaped me until just now...I have a maximum digging depth if I'm looking for brick material. I was well over that by using the dam floors.

I can't see anything in the report about an Atterburg limits test (which might explain why it was so cheap when I got it done 4-5 years ago). It's focus is waste-water management...which now makes me think I'm going to need to get another, proper, test done if/when I want to build. Ahh well.

Thanks for the help (and a bit of learning)

[jimbur]

From the post it sounds as if your block is in the Talbot area. Lots of mudbrick houses around there, some going back quite a while. Always worth talking with the home builders there.

[Rickey Herb]

If it was me I would just make a few test bricks and see how they go. Remove any obvious top soil and then use the subsoil. If they crack then the clay content is too high or they dried to quickly. Try adding some straw or slow down the drying time.

I wouldn't get too scientific - if you can make a brick that dries and holds together, then the soil is suitable. Must of the 'gold country' soil is ideal.

We have some soil that we carted in that appears to have a high level of silicates. It really doesn't appear to contain much clay at all but makes very good mud bricks (puddled) as well as compressed earth blocks.

Check out https://www.woodworkforums.com/f245/m...ferent-156967/if you are interested in compressed earth blocks as an alternative. We aren't actually using the silicate soil for the bricks but are using the soil that was excavated for the shed and tank. It is fairly high in clay. They are certainly easier than puddled mud bricks. A big advantage is that the bricks can be stacked straight off the press and covered if need be. Our press cost just over $3K to get made.

Hope that helps

Rickey

(Made 10,000 mud bricks for our first house and shedding and just about to start on our new house)

[RedShirtGuy]

jim: Yeh, there's some nice old places around the area. The hard part is finding the people who built them. I'm a bit more interested in ones that have been built more recently and had to deal with modern bureaucracy. Not that I expect a great deal, but that's where I'm guessing most of my hassles will come from when/if I get around to building a house.

Rickey: Great work in your photo gallery. I quite like the use of the tyres. At this stage I'm just farting around and seeing what my soil contains purely to satisfy my interest. Extracting the clay serves the purposes of finding out roughly what percentage of it I could expect and provides some material for pinching out a few earthenware pots and whatnot just for fun. I was planning to knock out a few puddled bricks for a BBQ to experiment with the mixes and have a bit of a practice of the whole process from making to laying as it's something I've done very little of before. A house is a very long term project - 5-10 years at least - and still might not get off the ground at all, but while I can, I figure it doesn't hurt to have a play

[Bushmiller]

RSG

Just a couple of comments from somebody who nearly built a mudbrick house (we designed it to be mud brick, but couldn't find suitable mud. I'll come back to that comment).

Make a mould and keep testing soil samples in a brick. There is a balance between sand and clay. Too much clay and it will crack and more significantly be unworkable. By that I mean it will be too sticky and won't come off a shovel or other implement. Too sandy and it will not hold together. Sandy soils are more suitable for pise (rammed earth).

A mud brick works by the platelets in the clay being brought together (and holding together) by vacuum as the brick dries. Ricky Herb is correct when he says if the brick holds together it is suitable for use. There is a qualification to that in that it has to be reasonably resistant to moisture. there is something that is called an "accelerated erosion test" to evaluate that.

Straw often needs to be added to mud bricks, although it is unclear as to why this works exactly: It just does, but is not always needed. There are theories around reinforcing and absorbsion of moisture, but nobody knows for sure.

The big decision is whether you use mechanical methods or hand methods to break down the soil prior to adding water. The soil needs to be broken down into extremely fine particles before use to ensure maximum saturation. If you cannot find suitable soil consider trucking material in. About two tipper loads would be enough for a house. In fact a house site excavated to 600mm will provide enough material for the mudbricks.

In our case we should have trucked material in, but in those days I was too much of a purist to even consider it.

The bottom two courses of mudbricks are often made in a different way in that they have a cement component to improve their durability. However, as with a pressed budbrick, they perform differently in that they are more pourous. Pressed bricks are considerably quicker to make and less labour intensive.

Oops, that was more than my "couple" of comments.

Regards
Paul

[RedShirtGuy]

Couple shmouple


I've already made up a metal mould for the BBQ bricks (which aren't as thick as house bricks would be because of the other cinder blocks I'm using for the BBQ) and yeh, the plan was to try a few different mixes to find a good one. As part of my playing around I was going to simulate the two erosion tests (one by droplets, one by spray) myself just to see for myself how different things in the mix effect the results.

As I've understood it the straw helps to wick away moisture from the middle of the brick for more even drying, and the long fibres of cereal stalks (or rice husks) give it a bit of strength. But yeh, it's not always necessary.

If the time comes where I'm actually going to go ahead with a house I was hoping to have piles of the separate materials ready to go for when it came to brick making time. That's something I can build up over time and could fill in those long winter nights...I've been quite enjoying sitting out in the peace and quiet sifting and mixing what I've been digging up. There's also the option of just making some bricks, having them approved and storing them for either building with or selling off.

Besides my goal for anything I make to be an example of sustainable building I also want to try and do it as cheaply as possible (who doesn't) and my current and future life situation has me with huge amounts of 'free' time to put in the manual work myself - it will only ever be me, myself and I doing this. The time-frame I'm looking at also allows the work to be spread out and a lot of preparation done before anything is really even needed.

Just recently I had a thought about using huge bluestone blocks for the bottom of the brick work. I haven't investigated it yet, but the idea is there. I can also get bricks of a different mixture for the bottom rows fired by a pottery mate. Again, I haven't looked into it too much and have just been playing around.

This has all been something I've wanted to do since I was about 6 years old and I've spent much time, on and off, researching and planning. The only thing that's holding me back is finances. I fear I'll spend more on permits etc than I will on the actual build...not that that matters now because I barely have two cents to my name...but when the time comes it will be interesting to see where and how I save the most money compared to an off the shelf house built by tradies and not DIY.

[jimbur]

Now a warning. Mud brick building seems to put a great stress on marriage. Know quite a few couples who broke up in the process or soon afterwards. It seems it's a long hard haul and a great strain on relationships. I suppose a dream is hard to maintain through years of mud, dust and hard physical work.
ps you've made me realise how old I am. I'm talking about thirty years ago and more.

[Bushmiller]

Now a warning. Mud brick building seems to put a great stress on marriage. Know quite a few couples who broke up in the process or soon afterwards. It seems it's a long hard haul and a great strain on relationships. I suppose a dream is hard to maintain through years of mud, dust and hard physical work.
ps you've made me realise how old I am. I'm talking about thirty years ago and more.

Jim

The effort required in house building is inversely proportional to the cost. Seeing as how the mud is dirt cheap ( ), the physical input is humungus. We lived in a small, very basic shed for some years with three children and you are absolutely right. It did put a strain on the relationship. In fact my daughter ( 9 years old at the time) moved out and lived in the tree house for the last six months of our time there. We were a bit too much for her ! She is not your average female .

Everything is OK while ever both (all in our case) parties enter the project with their eyes wide open.

Regards
Paul

[RedShirtGuy]

Heh yeh. I hear renovations can have the same effect.

Unfortunately, (or for this purpose only, fortunately), my marriage has been an unmitigated disaster. So while I'd rather circumstances were different, I can get back on the chase for this little dream of mine and not have it make things any worse. It's the silver lining I guess