Rammed earth bricks inside a waterproof building

[Catweazle]

I'm looking for a way to convert a steel skinned building into something that doesn't suffer such extremes of heat and cold. My original thought was to build a lightweight aerocement block wall inside, directly onto the substantial concrete floor, but this will be expensive. I can afford to lose the space the wall would use. My second thought is to build a press to make rammed earth blocks and build a wall with them instead. I have a 20 ton press and can fabricate a mould. Using linkages I could increase that 20 tons a few times if needed. The space used by supporting pillars will not be a problem, the building is large. Construction time is not a problem, there's no hurry.

My soil is sandy clay, which from my first tests seems suitable.

Does anyone have any suggestions or links that might help ? Google finds rammed earth made in forms or car tyres, but not so much info about making building blocks.

[BritDownUnder]

I think you will need a binding agent and a fibrous material to lend strength (compressive and tensile perhaps) to the block. The word 'sandy' does not inspire a lot of confidence.

Back in the olden days animal excrement and straw were used in such methods of construction. Indians and Africans have been making mud bricks for ages.

Not that I am trying to put you off - quite the opposite. Without research and development there will never be any progress. Keep trying.

[Catweazle]

Apparently sandy clay is suitable, and I have a patch of it conveniently far from the house that I don't use. Squeezing a handful together makes quite a firm ball. I'm not sure of what happens when subsoil is "rammed", but somehow it bonds together quite strongly. Optimum pressure ? I don't know, I'll bet the peak pressure when soil is bashed into a mould with a sledgehammer is surprisingly high, I'd prefer a less labour intensive method using hydraulics if it's possible.

Adding 5% cement to the mixture makes a waterproof brick that is also a lot stronger, but not so green.

[kenneal - lagger]

You can make earth bricks with a hand lever press: you don't need an hydraulic press nor huge pressure.

Test the soil for clay content by placing a sample in a glass jar, half full will do, and fill it almost to the top with water. Shake it up and leave it for a few hours to soak and break up then shake it up well and leave to settle over night. You can then see the different layers in the jar. Sand and stones will be at the bottom, then silt and finally clay at the top. Clay should be at least 25% of the soil volume.

Another test is to moisten the soil so that it sticks together and then take a pinch and roll it out to make a worm in the palm of your hand. If you can make a worm 3 or 4mm thick you have enough clay in the mixture to bind the soil.

If the soil has enough clay spread some out on a tarp, saturate it and add a covering of straw. Put another layer of soil on top and add more straw and a bit of water then tread the whole lot together. When it is well mixed and spread out roll the tarp over so that you get a sausage of soil. If any bits are still dry, add more water and some straw on top and tread again. Roll and repeat a few times until you have an homogenous, moist mix. Fill you mould, press the brick, push it out and place somewhere to dry slowly. The dryer you can make then the sooner they will be dry enough to use and the less they will shrink. Try to keep the moisture content of each batch similar so that the bricks end up the same size.

To lay the bricks make a thick slurry of the sieved soil and use that as a very thin mortar to bond the bricks. Do not use cement anywhere as it will inhibit moisture movement through the wall. I would add a layer of insulation between the steel and the earth to reduce heat movement into the internal space and also ensure that there is a movement of air up the inside of the steel skin and out at the top to remove any moisture from the structure.

You will be able to enrol in the CAT course on earth building that I probably run there next year very soon if you wish for some hands on experience. Apparently it sells out quite quickly, I was told at this year's course.

Alternatively you could build an insulated timber framed wall inside but again ensure that any condensation from vapour movement can escape the steel skin. There are a number of ways that the roof can be treated including insulating over the current roof and laying a new roof over that. Again allowing for vapour escape is essential.

[adam2]

Earth bricks or blocks will need some form of fibre reinforcement. Traditionally straw or animal hair was used, modern alternatives include polyester fibres from shredded tarpaulins or woven sacks, or teased apart scrap rope.

Another alternative is to add Portland cement to the mix, as little as 5% will greatly improve the blocks. But even 5% cement adds significantly to the costs, both enviromental and financial.

Edited to add, Kenneal, whom I understand is professionally qualified in such matters, has cast significant doubts as to the wisdom of adding cement, see following posts for details.

[kenneal - lagger]

I must disagree, Adam. Adding cement will not greatly improve the blocks. It will greatly impair their utility and is not required at all.

[adam2]

I must disagree, Adam. Adding cement will not greatly improve the blocks. It will greatly impair their utility and is not required at all.

Are you certain ? Earth bricks with a little cement are very widely used in Ghana and seem to give satisfaction.

[kenneal - lagger]

The cement kills the ability to pass water vapour and reduces that water absorption ability of the brick. This is possibly not a problem is tropical Ghana but could be a problem in colder and wetter here.

[adam2]

I have edited my post to reflect your expertise in such matters.