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Adobe brick making #1: Trial mixes

Blog entry by daltxguy posted 02-04-2009 12:41 PM 9070 reads 1 time favorited 13 comments Add to Favorites Watch
no previous part Part 1 of Adobe brick making series Part 2: Some adobe brick abodes »

Several years ago now, my partner and I took a 1 week course on building with adobe bricks/cob. We are lucky here in New Zealand that some hard working people developed approved building standards for adobe brick construction. Our instructor, Richard Walker was one of the people responsible for this standard.

Our forest property sits on some ideal clay soil and we are interested in sourcing our new construction entirely from materials found on or near the site, so adobe should figure somewhere into our plans.

We did some experiments to test the suitability of our clay and the contents of our soil ( I wasn’t going to cover that here unless someone is interested but suffice it to say that 1 simple test is to fill a jar 3/4 with your soil sample add water and shake – when it settles out measure the layers of sand vs silt vs clay and determine the ratios of each). We determined that our soil was upwards of 50% clay and so was well within the range of suitability.

We made some test bricks about 1 1/2 years ago. A simple quality test we ran after about 8 weeks of drying our bricks – a drop test onto the corner of the brick from about 3 feet up onto a hard surface – indicated that our bricks were weak. It formed cracks along the entire length and the true benchmark was that greater than fist size chunks broke off.

Our conclusion was that we have too much clay in our soil, so this summer we wanted to try another experiment to determine a proper mix.

We got another load of soil from where we would most likely be digging our soil out. The location is ideal for brick making because it is flat ( it’s our logging skid site), open to the sun ( for drying bricks) and near a creek ( for a source of water). We dragged it back however to our current house and prepared 4 different mixes:

  1. Clay and extra straw – we thought maybe we didn’t have enough binder so we added extra straw this time.
  2. Clay and straw and some sand. We found a source of sand near the river which runs adjacent to our property, grabbed a couple of buckets of it and added 3 handfuls per brick to the mix from #1.The sand cuts the percentage of clay in the mix. The amount wasn’t very scientifically derived but we figure if we see a difference then we may try another experiment with varying amounts of sand.
  3. Clay and wood chips. Because this area is not known for much wheat or grain production, any straw we would use would have to be transported from across the country. As this doesn’t quite meet our criteria of sourcing from onsite or nearby materials, we thought we would try woodchips. There is a mill in town and they have mountains of these woodchips. We got a good tubful for our test. We’re also hoping that the woodchip brick might be a tad lighter and have better insulation properties.
  4. To #3 we again added 3 handfuls of sand per brick and made two more test bricks.

The bricks were formed with our wood form. I have to say the woodchip mixes were the easiest to form, but this may also be because by that time the form had been well soaked. I definitely recommend presoaking the wood mold. On our course we used a metal mold. I might just weld up a metal one and see which one we prefer. I think though the steel one is less sticky and therefore the brick comes out cleaner and easier.

We now have the bricks drying. Since February is our driest, hottest month, it might only take 4 weeks or so for the bricks to harden up and dry out, but we’ll probably leave it for 8 weeks.

We formed the bricks on a concrete pad which is inside a shed in the back of our garage.

Next entry will explore the results.



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daltxguy

31 posts in 4066 days

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13 comments so far

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MRTRIM

743 posts in 4245 days

posted 02-12-2009 04:38 AM

quite interesting post . are they actual building blocks ?

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daltxguy

31 posts in 4066 days

posted 02-12-2009 07:53 AM

Thanks MRTRIM.

Yes, these would be actual building blocks. It’s the standard size used around here – just under 12”x12”x6” so that when it is placed on the wall with mud mortar, each brick is as close to exact 12×12x6 as possible. This size makes it easier to estimate the number of bricks and produces a 1ft thick wall.

The mold size takes into account the shrinkage of the bricks when they are dried. This was established by making a test box filled with mud, measured after fully dry. I think we had quite a large shrinkage factor due to the amount of clay in our mix ( I think it might have been around 7%).

You can make larger bricks too, but then it becomes a matter of weight. These already weigh on the order of 20kg (44lbs) apiece. We make 1 1/2 size bricks for the corners, so you can create a locking bond pattern.

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MRTRIM

743 posts in 4245 days

posted 02-12-2009 01:07 PM

so your building something with these blocks ? id like to see a pic of something built with these . what keeps weeds and grass from growing out of them ? id sure hate to have to mow my lawn and my house too ! lol

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daltxguy

31 posts in 4066 days

posted 02-14-2009 10:57 PM

Hi MRTRIM,

These blocks are only being used for evaluation but these are the very blocks I would use for any building I would do. The beauty of earth blocks is that when your experiments are over, you just bust up the block and put it back where it came from.

No chance of grass growing out of the blocks because there are no seeds in the mix. The binder is straw or woodchips and the blocks are only ready to be made into a structure when they are completely dry. Add sufficient water to a mud brick and it becomes mud again, so the most important aspect of mud brick building is keeping the elements off of the bricks.

In mud brick building, they say “good hat, good boots” is the key ( as it should be for any building method really), so care is taken that there is a good barrier between the foundation and the bricks and that the eaves are sufficient size to keep weather off of the walls ( usually a min of 3ft eaves for a single story building).

The other thing which can be done is to further waterproof walls is applying a lime plaster. This provides a breathable membrane but prevents water penetration. No water = no chance for anything to grow on the walls including algae or moss which is more likely than grass. These are basic principles applicable to any house building.

On the other hand, if your lawn and house were covered in grass, it would be the ultimate in green building :)

I’ll post some pictures of some structures built around here with these kinds of bricks later. You will see that they look like ‘normal’ houses!

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PaBull

694 posts in 4191 days

posted 02-16-2009 05:28 PM

Daltxguy, we like to see the building, what are you putting together…

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MRTRIM

743 posts in 4245 days

posted 02-18-2009 02:13 PM

thx guy , im finding this quite interesting . thx for sharing it .

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dennis

90 posts in 4245 days

posted 02-19-2009 06:33 AM

It sounds familiar. My strawbale house is finished (someday) with a layer of cob. Yes Mrtrim it is not easy to run the lawn mower up the outside walls so I make my wife do it. Actually They are pretty weed free.

-- http://woodsongsfurniture.com

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MRTRIM

743 posts in 4245 days

posted 02-19-2009 01:13 PM

ha ha dennis thats why i was concerned about it , im not married ! lol

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PaBull

694 posts in 4191 days

posted 02-20-2009 01:37 AM

My wife is getting behind with mowing our house.

View dustygirl's profile

dustygirl

321 posts in 4032 days

posted 02-21-2009 04:46 PM

Very interesting post.Thanks for sharing it.I too would love to see the progress of this project.
Ha ha good one Dennis and PaBull.

-- Dustygirl Hastings,Ont. Life is too short to sit around doing nothing

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Radicalfarmergal

10 posts in 3324 days

posted 10-12-2010 03:16 AM

Hello Steve! I did not know you were on HR as well. I just stumbled on your adobe posts. Very interesting. How did your second batch of bricks turn out? Have you tried any more? If your adobe bricks don’t work out, you can also look into earthbag construction as an alternative. Using the polypropylene bags to hold the soil means that your filling material does not have to be as strong as the adobe bricks need to be.

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daltxguy

31 posts in 4066 days

posted 10-12-2010 09:44 AM

Hi Robin,

Ok, well I left the brick for longer than 8 weeks – more like 88 weeks. Those bricks were made when we still living in Christchurch and making the permanent move to Murchison – so the bricks were 250 miles away. Then it was the move and last summer was spent insulating the house for the winter just past.

So the bricks are still there and the tests haven’t been completed. I can say that it looks like adding extra sand has improved the mix. The addition of both woodchips and sand has produced a strong and lighter brick. In the end it’s not a question of if they would work, it’s just a question of getting the right mix.

Earthbag construction has attracted my interest as it is a earth product but I have rejected it as an option for me for 3 reasons: 1. You need a lot of polypro bags, which I don’t favor because I don’t want plastic in my walls or oil based products. 2.Usually earthbag construction uses cement reinforced earth. In my opinion, this takes away the very properties which make earth a good building material – the earth loses its’s ability to absorb and release moisture 3. Our earth building standards in NZ does not cover earthbag construction, meaning that slightly more engineering needs to take place ( earthquakes being the primary concern). With adobe bricks, rebar reinforcement can be built in as you build.

Having said that, I am now favoring roundwood timber framing construction ( timber framing with whole logs) and using adobe brick or earth plaster infill ( ie: as non load bearing walls for interior only walls mainly for radiant heating and as a solar flywheel ). There are many reasons for this but it makes better use of our materials onsite with less processing, and it appeals to my woodworking obsession too.

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PaBull

694 posts in 4191 days

posted 10-12-2010 04:44 PM

Thanks for picking up the thread again!

Are there any pictures of your Christchurch?

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