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Comment by phpnode | Hacker News Reader

The video makes the point that a single bag of cement costs €20 in an area where the average daily wage is €10.

I bet peaches are expensive in that area too, because there are no peach trees.

Concrete costs about $160 USD per cubic meter both in the USA and in Zaire (first African country I cound find a price), that works out to $4 USD a 35 kg bag, but in this case it's mixed and ready to pour.

If concrete factories were more common there there, I'm sure the price would be comparable for a material that is easier to work with, requires far less labor, etc etc. But they don't, and their traditional techniques work well for the area they're in. The moral to this story is, use what's local and does the job, and I feel like the only thing I got out of the video is some cool visuals of dudes building with bricks.

Of course, clay has a lot of benefits over concrete. It's lighter, insulates better, they can dig it out of the ground!

> The moral to this story is, use what's local and does the job

The content of the video is specifically directed at people of the developing world:

> this is the catastrophic reality I say in developing countries we have to go back to using natural building materials. historically we have a very rich examples of vernacular architecture that still stands we have to go back to our traditions to learn from but in the same time keeping up with the immense scientific progress so that a person from the 21st century can enjoy modern life commodities examples from South of France and Germany

Promoting locally available building materials for building houses is very different than saying one shouldn't incur any debt when building a home.

I guess titles for any documentary are going to be at least a bit intriguing, which could be the same as clickbait? But the full YouTube video title does specify it's talking about/to Africa:

"i'd rather build my house with my own earth than go into debt, Green Architecture, Africa"

I don't know quantities here - how would a bag of cement compare to two days' worth of hand-making bricks in terms of building materials?

I think a bag of cement would go a very long way for making mortar for a rock wall. Why make bricks when you can just use rocks and stick them together with a little bit of cement.

Bricks were made for uniformity so you could have it as a known quantity and spit them out of an assembly line. If you're making bricks, you've already lost this game.

The video at 6:11 briefly touches on making mortar and stone construction (along with visuals):

> binding material or mortar should be of the same constituency as the brick or stone white gypsum and sand mortar go well with sandstone mortar made of lime clay and sand is suitable for our newly developed mud bricks

https://youtu.be/f_q1pYl80pc?si=sP1GwbWT3UfFVsBW&t=371

Very favorably. Think of how big a bag of cement is. Using a timber mold like the one used in the video you can leave 100s (if not 1000s) of bricks to dry in one day. You need some materials like clay soil, straw and sand, some which might be sourced on-site. It might take a day or two in hot sun for the bricks to dry, but this can be done in large batches with enough space. They also can be fired in a kiln for extra strength, but that would forgo some CO2 benefits.

You know cement is not used to make the bricks right?

On one hand I'll refer you to the comment I was replying to:

https://news.ycombinator.com/item?id=37927320

On the other I'll point you to this common structural building material:

https://en.wikipedia.org/wiki/Concrete_block

25kg of cement is roughly 12L of 'concrete. 12L is 20cmx30x20cm (8x12x8 inches for the freedom loving folks)

From a quick Google search: 1m3 of concrete = 150l water + 250kg cement + 700kg sand + 1200kg aggregates.

Even if you used just cement and water I think you would get more than 12L from 25kg.

True, I meant pre-mixed bag of cement + sand.

>Even if you used just cement and water I think you would get more than 12L from 25kg.

The thing will crack very soon. The density of concrete is around 2.4g/cm3

a lot of that would be transport costs. So unless there are to produce the brick locally (and w/o a kiln - which would require something to burn), they are to experience similar issue with costs of the bricks.

In the video they are building the bricks on-site. I've done this before. And also built a kiln on-site with mud bricks (with a small team), though it takes a good design to get it to the high temperature required. Rammed earth is another natural building alternative where a formwork is built in-situ, infilled, and tamped down, once again with on-site materials. And from what I've seen it's absurdly strong, and can be polished such that it reflects like marble.

For extra challenge, any idea if a solar kiln could be practically used for mud bricks?

You need a temperature of about 1000°C to fire bricks, but more is better to get the moisture out. From cursory googling around it seems that a solar kiln wouldn't cut it, unless perhaps a very large solar collector was used... which upon further cursory googling yielded this:

https://helioscsp.com/concentrated-solar-power-for-high-temp...

https://cordis.europa.eu/article/id/421794-the-next-solar-re...

Interesting, thanks. :)

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