Cast In-situ Adobe Construction

You can make adobe blocks directly on the wall with molds to save time and labor.
You can make adobe blocks directly on the wall with molds to save time and labor.

Typical adobe construction involves making adobe blocks by digging and mixing mud, filling molds with the mixture, drying the blocks in the sun, turning the blocks every so often, moving the blocks to cure under cover, and then moving them to the jobsite where they are often moved several more times in the course of constructing the wall. A typical New Mexico size brick is four inches thick, ten inches wide, and fourteen inches long (4x10x14). A brick this size will weigh about thirty pounds. Obviously building with adobes is a slow, labor intensive process. (Despite the drawbacks, adobe is still one of my favorite natural building methods due to the low environmental impact, widespread applicability, relative simplicity and beautiful finished appearance.)

But what if the adobes could be cast directly on the wall and never moved? Ahh… this would cut out numerous steps and greatly speed the process several fold. You could make your own forms or buy pre-built forms by a company such as Formblock.

“FORMBLOCK is a wall building system in which stabilized earth, or concrete blocks are cast in-situ to produce a solid load bearing wall. In use now for over 15 years in a range of conditions throughout Australia and New Zealand, it has been thoroughly tested by professionals, architects and owner builders.

The FORMBLOCK Wall Kit is designed in 300 millimetre modular units that is easily assembled to produce a course of blocks, each 600 mm long, 300 mm high, 300 mm thick, it fits neatly with other conventional building systems.

The FORMBLOCK method significantly reduces the labour required to produce an earth wall to only fraction of that compared to adobe (mud brick) or pisé (rammed earth) methods of earth building. As the handling of the earth material is minimised, by the in-situ nature of block making. Once the blocks are poured, the wall is effectively complete, with no further need of on going maintenance, making the FORMBLOCK system a cost effective and affordable method of masonry wall construction.

The FORMBLOCK Wall Kit requires no expert skill, it is easy to use and simple to understand and is ideally suited to tradespersons, owner builders, and handypersons, alike.

The FORMBLOCK Wall Building Kit conserves natural resources. By producing earth-based blocks, you will contribute in saving global energy otherwise used by industry to produce other building materials, such as fired bricks, etc. as well as the thermal properties of the walls giving you ongoing savings in heating energy.

Less reliance on timber, means less deforestation. The FORMBLOCK system is NOT a wasteful ‘once only use’ formwork, it is designed and made for long lasting repeated use.”

Estimated wall cost: Free earth plus cement using 9 parts earth : 1 part cement, equals approximately $23-$50 per sqm wall area. Check for availability of used FORMBLOCK molds. The molds could be used on future projects or sold when your house is finished.


More information:
There’s a risk of cracking in cast in-situ adobe walls, so take care to test the soil mix carefully.
Other materials such as hempcrete, and gypsum and lime-stabilized soil could be used. Hydrated lime can be used in place of cement.
In-situ adobe is ideal for curved walls, which can be made with curved sheetmetal molds.
Rebar can be used inside the walls to add strength when building in seismic zones.
Nice photos of custom homes made with in-situ adobe at Ecodesign
Vene block timber molds See slideshow: Low Cost Construction
You can make your own molds. They can be very simple or made more complex.
I believe The Owner Builder Journal in Australia has articles about this building method in back issues.

33 thoughts on “Cast In-situ Adobe Construction”

  1. Thank you for posting this! im in AZ and im planning to go adobe and my home ive designed round rooms on 3 corners and plan to go up 2 stories. this is perfect for what i have in mind to build. i will be experimenting with the soil i have on location and making a small test wall and some test bricks to make sure its good. im also looking up what ever engendered “code” recommendations for thickness vs height. so im not making myself a grave lol. we are gonna test next month and play in the mud. gonna go with a portland mix and i plan to add mesh between runs maybe rebar. concrete headers for the 2nd floor. thinking i may do a run every weekend or every 2nd weekends depending on dry time. im looking forward to it. thank you again

  2. My experience with plaster of paris is that it erodes/disolves in water, so that it should not be used in contact with earth, or expected to be structural. I am no expert in plaster of paris. Maybe there is some additive that would waterproof it- don’t know.

  3. Looking for any info on cast earth homes that are part Soil, Sand and Plaster of Paris. Its pumped into freestanding wall forms which are taken down next day, leaving a house just needing a roof.

    • The main information is on Kelly’s Green website. This would be a fantastic way to build except the inventor is keeping the formula to himself and charging unreasonably high fees. Consequently, only a handful of buildings have been completed in decades. Tip: I know a science professor who said he thinks he knows how it’s done. How hard can it be? It’s probably a few basic materials. If you’re really interested, consider doing small scale experiments for non-profit use.

  4. I’ve been trying to explain the pure beauty of the sand cast homes I saw in New Mexico, with striations varying with sand color changes. Now I can’t even find any on the internet. Could you please just text me the name of any contractor that works in this medium. I was told that there is sand and plaster of paris so forms can come down the same day. Any help would be appreciated.

    John Pavelka

  5. Has anyone tried this with hempcrete? Living in Canada, adobe is pretty much useless for a house, but hempcrete has great R-value.

    • It will work. Just realize you’ll still need a structural system like post and beam to carry the loads because hempcrete is non-structural.

  6. I used rammed earth with simple plywood form work, pipe clamps and 2x bracing. We put up the forms in less than half an hour fillied and tamped four feet added two more plywood sheets and finished a 18″ thuck x 6 foot wide and 8 foot tall wall in half a day. Due to earthquake requirements in our region had to add rebar and small amount of cement. But rammed earth has been effective in many regions for centuries.

    • Yes, rammed earth is one of the better natural building methods. No plaster is required, and the finished appearance can be exceptionally beautiful. Big projects are typically done by contractors with lots of expensive forms and pneumatic tampers, so I don’t talk much about it here on this blog. But your example shows how it is possible to do it on a smaller, lower cost scale. This is definitely possible. After all, people have been doing rammed earth for thousands of years using simple equipment. See this previous story about Ancient Rammed Earth Structures that have survived thousands of years. It’s amazing.

  7. Question for Owen and the group, I have a lot up in West Virginia, that I would love to use this technique to build our homestead in the making. my question is, is this building method best for arid/desert regions or would it work in the north east. my problem is that im building in WV but I live in Atlanta. I have to schedule the trip up about a month or so in advance and then my wife and I have just one week to get done what we can. In your opinion, Is Alker something that we can work on, and then be able to leave without worrying about rain/weather dissolving the walls until its under roof? I would really like to use a natural wall technique, but if I have to , I can always go with dry stacked block. if rain doesn’t bother Alker , it would be awesome to be able to make a trip to WV, pour what blocks we can get done in a week, and then come back to Atlanta. then repeat until the house is done.

    • It’s never good to leave a building exposed to the elements. I suggest building a post and beam frame and getting the roof finished. Then you can work a little at a time using whatever wall technique you want. Maybe even use 2-3 methods for visual interest and experimentation. See the blog post the other day about recycled wood post and beam buildings. Then study the Dunne family’s project that we profiled.

      • Thanks Owen, I’ll check out those post. I was actually thinking of doing post and beam, but I was a bit worried about the building setting there with no walls filled in through the winter. Specifically about wind lifting the roof. We have the rubble trench in, I just need to pour the grade beam, and I’m ready to start building. That is if I can pick building medium…
        Thanks again, I sure do love reading your posts!!

        • It’s very unlikely the roof would blow off if you use the appropriate type and number of hurricane ties.

          Make sure to provide adequate roof overhangs to protect the walls.

    • Similar but different. Poured earth is poured into large forms. It uses a proprietary (at least at this time) formula. It lends itself to larger contractor jobs.

      Cast in-situ is much simpler, lower tech and lower cost. You can do a little at a time at your own pace.

  8. This type of wall construction would work well with a foam concrete we made with New Mexico blow sand and foam cement.
    We made test samples which weighed 35 # per cu. ft. and had tested at 800psi compression strength. The mix was one part cement, one part blow sand and 6 parts foam. The high air content in the mix leaves an insulated wall instead of an energy sucking solid adobe or concrete wall. The material is soft enough to carve, and would need a stucco finish inside and out.
    The foamer is very inexpensive, but the cement needed is the same as normal concrete.

    • Very good. Thanks for sharing. If you have photos (even 1-2 good ones) and more info we’d love to turn this suggestion into a new blog post.

    • I have been looking into the foam concrete and I cannot find a inexpensive machine to make it. Do you have a link or an address so I can make an inquiry?

      • There are no inexpensive machines for making the foam, but I would sell you mine for $2000. These are metering machines that can deliver the correct amount to a concrete truck or pumper.
        For diy you can use a bucket or 30 gallon drum, put the foamer in, and use a high speed drill with a circular brush on the end of a long shaft to create the foam. This then gets added to the correct cement/water/sand for the final product.
        We did this for my roof insulation in mexico.
        I have also made the foam with a home made foamer tube and compressed air. The tube is 1″ diameter x 12″ long stuffed with stainless steel wool. The foamer gets sucked into the tube via a venturi .
        I should put together a some plans for these.

  9. Owen

    Is it reasonable to use Alker technology instead of cement with a Scoria base to get a solid wall that is insulated as well? Or would a lime cement be better. I know the gypsum in alker sets up fast but if you are one person doing a block at a time you should be able to pour the mix into a mold before it sets up, basically doing a batch per block. The quality control should be easy as you are doing a small amount of mix each time and sticking to the same formula each time.

    Would it be true if you built a round building you should need basically only one type/size of form as no corners or weak points.

    Would it be better if a mold has keys or notches to interlock the surrounding blocks together as well? The thinking was you would never has a straight path for air to leak in if there was a shift in the blocks or a crack in a seam formed. Here in New Zealand we are seismic active so you have to think about these potential future issues.

    Sorry for all the stupid questions but I have pondered on this type of building for a long time.


    • The Formblock molds have an interlocking feature. That’s just one of the advantages of that system.

      You could add scoria to an Alker mix or similar mix, although you won’t gain much insulation before it starts to weaken the blocks.

      The ability to pour one block at a time is a key advantage for owner-builders. Note the comment above where poured earth requires large forms, concrete pumping equipment, etc.

      This would work great on roundhouses if you can build the molds.

      Everything changes though when you start factoring in codes. They won’t let you build your own molds and use an unproven design.

  10. We built our first home is a similar fashion, with home made forms like that. We have them bolt together, 2 people could set up in a few minutes, have them pop off just as quickly. We made the form come apart from the sides, so we could use remesh to reinforce the wall.

    We eventually migrated to a more refined version, called the T brick (info on this page:

    With T bricks, the form was shallower, and the mortar space between the lower course was a bit wider. Also, because of the flaps, they were mostly self-leveling. The adobe sets up up quick enough in the T bricks in a few minutes to take the form right off and pour the next set of bricks, making it go much faster.

    We had a neighbor in West Texas that put a form on a long arm and did insitu adobe blocks to build a cylinder. A similar approach could be done to do a dome, but you’d want each layer to dry a decent amount before attaching the next layer. In straight walls, you don’t have this issue.

    • Great suggestions. Abe’s homestead is like a living laboratory. I’ve been reading his site for years. Are the T form building details in your new book? I haven’t studied this lately so can’t remember if the website info is clear enough to build from.

      Also wanted to add that Abe’s experience (very well documented work in Texas) is more proof of concept of cast in-situ adobe. This subject is worth more research since adobe is probably the number one most common building method in the world. Countless millions of people live in adobe houses. They like their homes and it’s affordable to even the poorest people.

      • No, the new book is solely about food, but the Tbricks are on the link I posted. They are pretty simple, really.

        That house in Texas is now a decade old, doesn’t even have plaster, and it’s still standing without issues.

        in-situ adobe can be done a lot of ways, and it really is a move in the right direction.

        • Thank you very much Abe. This is interesting and encouraging information. If you have time, can you tell me approximately how much faster your T block system is than regular adobe? It sounds like it’s several times faster, correct?

          • To be honest, I don’t know, because we never did a side by side test.

            But, with regular adobe, you mix it, make the blocks, and then cure the blocks for 28 days. Then you make the house.

            With Tbricks, you pour right on the wall and they cure in place. So you save at least 28 days. You also don’t have to lift the material multiple times, so you save a bit of your back, too.

            The mixing and pouring will be similar time for both methods.

            The Tbricks are faster than bigger forms, like the FORMBLOCK systems, because they just slip off after a few minutes after the pour. This also allows you to have less forms, because you don’t need enough to make a whole level, just a few bricks.

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