This is the follow-up to my video on rammed earth, the world's healthiest building material. That one got flooded with hundreds of questions I didn't have all the answers to, so I contacted my friend Mercedes from Seal Construct and drove out to one of her build sites, where she educated me on the details. What follows is her answers to the questions you sent, plus the parts I could answer myself.
Will It Survive Where You Live?
The first pocket of questions all centered on whether it survives where you live specifically, and how it performs in other climates. A lot of people were concerned that because it's made out of dirt, it's just going to wash away whenever the weather comes.
Mercedes' answer was about the mix behind the wall we were standing next to. Her team has gone to all the different quarries around, selected the material, and worked with SIREWALL, who she says creates the best mix designs. That particular wall is sitting at 4,000 PSI. In her words, it's going to be all right: it's not going to crumble and it's not going to deteriorate. On the inside they're also using pneumatic rammers, which run on compressed air.
What's Actually In The Mix
I asked what percentage of a rammed earth build is actually earthen material versus cement versus stabilizer.
It varies based on your mix design. The better you can get all those pieces to come together, probably the less cement you need to bind them efficiently. The wall we were looking at, at 4,000 PSI, is about 10% cement.
Some people try to use less because they're trying to be more environmentally conscious. Mercedes' view is that this is something to discuss with the architect and the engineer. If lowering cement is the goal, maybe you don't have the walls be load-bearing, and other load-bearing members support the weight of the roof instead. But maybe where you are, the materials are just what they are, so you might have to increase the cement, or whatever your binding agent is.
The Tetris part
She describes creating a mix design as playing the best game of Tetris you can with your sands, your aggregates and a little bit of cement. You're trying to get all the pieces to fit as tightly together as possible. If the mix design isn't correct and you have too many large particles or too many fine particles, you won't get good compaction. She showed it with the rocks she was holding: you can squeeze them together all you want, but there are gaps in them. You need other elements of other sizes to go in and fill those gaps. Maybe it's a 50/50, maybe a 1-1-2, maybe a 1-3. A little bit of cement fills in even the finer stuff and gives you the chemical binder you need.
It's Not A Mud Hut
There was a bit of confusion around whether this is like a mud house, and whether it could erode over time.
Here's the distinction I want to give you. It's not a mud hut. It's earthen material, so it's more like gravel and sand and different types of materials that all fit together. And the really big distinction is that it's not organic material, it's inorganic material. There's nothing with life inside the walls. There are other alternative building methods where you do have life inside the wall. This doesn't have that, and for that reason it's much stronger.
It's still very important when you're building a healthy home that it can shed water. That means really good roof overhangs, so the wall isn't just being hammered by the weather nonstop, especially if you live in one of those climates where that's more possible.
If you hire a builder rather than doing it yourself, there's going to be some percentage of cement, usually sub 10% or right around 10%, and then there's the added silicone mix as well.
The Additive
The additive goes into the mix while you're ramming. Mercedes had me watch what happens when you splash water on the finished wall: it bounces off and just runs, with really good even coverage all the way around. It almost looks like glass to me, like a finish on the exterior of it.
But it isn't just an exterior treatment. It's mixed into the entire mix, so it isn't something you come back and redo like a concrete sealer. What she likes about the SIREWALL additive is that it's incorporated into the whole thing, and it's non-toxic. It also stays breathable. With a concrete sealer you're kind of blocking off the breathability. Here you still get that open vapor barrier, but it pushes the water out.
Freeze And Thaw
Some people asked about colder temperatures, and whether freeze and thaw is going to make it crack.
You can definitely get some cracking, but Mercedes says the majority of that will probably happen with the lower PSI rammed earth. What she explained to me is that as long as you're not building in freezing temperatures while you're doing the actual build itself, once it's cured it should be totally fine.
Humid And Tropical Climates
The next question was whether it can actually be mold resistant in more humid or tropical climates. The answer is yes. These types of builds actually perform extremely well in humid climates, because they buffer humidity. As long as they stay vapor open, which means the walls can breathe, the wall sucks up the humidity in the indoor environment, and then as humidity comes down it gently releases that moisture back into the environment.
That's the whole point of building with rammed earth: it's mold-proof and it's lower toxin, if not as low toxin as you can be. Those two things are the two most important elements of having a healthy home, because in the modern world we're spending more and more time indoors, so we need our environments to be as healthy as possible.
Pests, Termites And Rodents
You don't have to worry about any of that, because there are no wall cavities. And usually when you build rammed earth, you build it on a slab. So it's slab, then earth and wall, and nothing in between. Nothing can get into those walls.
Earthquakes And Tornadoes
Rigid mass wall performance will always come down to the mix design. SIREWALL always shoots for 3,000 PSI and above, and that'll hold up pretty well.
Mercedes said that if you live in a place like California, you definitely might want to consider putting some rebar inside to give it extra support. My own caution on that is if moisture gets in and the rebar starts to rust, it can expand and crack the stone. Instead you might want to opt for something like basalt fiber, which can't rust but will still give your walls that extra support, especially if you live somewhere with a high likelihood of earthquakes.
Radon, And Where The Material Comes From
A lot of people asked whether using earthen material means you should be concerned about radon. Mercedes' answer went to where the material comes from.
Most rammed earth builders in first-world countries, where there's a lot more thought and intent and design going into it, aren't building with the materials from right behind you. They're not using what's in your own backyard, because there are so many organics in there. She quoted SIREWALL on it: we love organics in our body, but not in our wall. Organics break down, and in nature that's the beauty of it. Grass decomposes, trees die. But if that's in your wall and it starts to break down over time, now you have weak spots in your wall.
I asked her what an inorganic wall actually means in practice. There's no life in the wall. No living organism, nothing that was living in there that can decompose and break down. The 2x4s that are in our houses will eventually decompose and break down.
Plumbing, Electrical And HVAC
The next pocket of questions all centered on the logistics. Once the walls are built, what about plumbing, what about electrical, what about HVAC?
Her answer: there are two ways to do it, depending on how much access you want to have:
- Run it inside the wall. Before they start dumping dirt in there, you get your trades in to run whatever pipes or conduit you need beforehand.
- Use a more exposed method, like a secret panel at the bottom or the top, where the pipes are hidden right there in the wall behind a baseboard or a piece of trim.
Hanging things on the walls
She says you can think short-term or you can think long-term. Long-term, you install some kind of track at the top of the wall that lets you change things out on wires, for picture frames and things like that. Short-term, you just drill right into it, just like you would with concrete.
The Rest Of The House
Is the whole thing made out of rammed earth? Mercedes told me that usually you're not going to be building a whole home out of rammed earth. Usually it's just the walls, so most of the time it's going to be some type of hybrid.
That's something to think about if this is what you want to do. Make sure you're getting the healthiest roof possible, the healthiest floors possible, and the healthiest materials you can for anything else that might be a really integral component.
Can You Modify It Later?
Not really. It's extremely challenging, so it's basically permanent, and there are pros and cons to that. Once you build it, it's going to stand the test of time. It's going to be there forever and it's not going to decay. That's kind of the magic of rammed earth. But you also need to be clear about what you want, knowing that you're making almost a lifelong commitment.
What It Costs
Mercedes wasn't able to give me a cost for building a whole home, because she just focuses on the walls. Here's how she ballparked the walls themselves:
- Doing it yourself, bare bones, nothing fancy: she thinks you could get it down to $180 to $250 per square foot. That's per square foot of wall, not cost per square foot of the house.
- Hiring people to do it: definitely around $250.
Permits, Loans And Insurance
Not every town and not every city is quite so loving with the word rammed earth. They don't have rammed earth written into their code, and Mercedes says that's okay. Her team can try to send it back through as an engineered dry pack concrete: very similar ingredients, different proportions, different outcomes.
I asked whether that's consistent with getting a loan too, not just permits. You're definitely going to want to talk to different banks, and they're all going to have different feelings about it. But they're going to feel a lot better if you have provable PSI from a crushed cylinder test, showing something with the same strength as concrete. It also helps to come in with some visuals, because you can say the words rammed earth over and over again and a lot of people still need to see it.
On insurance, she was straight with me that she hasn't had to explore it. She's hoping it's fairly comparable to concrete, because you have a product that's fireproof and pest-proof, and you could probably drive a car into the wall and it's not going to make much of a dent, so she thinks the risk side is pretty good there.
Why Rammed Earth Over Adobe, Cob And Straw Bale
I got a lot of suggestions in the comment section to look into other building methods, and I am, so there'll be more videos coming. But Mercedes made an important distinction that I think you need to hear if you're considering building a healthy home.
Growing up in New Mexico, she'd seen adobe houses. When she looked at adobe, cob and straw bale, frankly she didn't like the aesthetics of them. They looked a little bit too hippity-dippity to her: nothing that's going to be resellable, nothing that's really going to make people go wow and want to put it in a magazine. When she found rammed earth and saw the strengths those walls were able to achieve, that connected with her more morally. It was very strong, it was going to be long-lasting, and it was going to be able to take a beating in all different types of weather and still stand.
With some of those other methods, you get hit with too much rain and it really is going to wash away, or you run into a mold factor. I asked if that's because of the organic material in adobe, and her answer was that they've all got some kind of straw or hay or something in them.
My Take
As you can see, building with rammed earth is not a simple process. But I still think it's one of the best options out there if you want to build a healthy home.
