Earth floor question.

I recently saw a video in which a family first leveled the ground. Then basically tossed dry concrete on top. They then used a tiller to mix the concrete and dirt. Another person was sprinkling water over the top after it was all mixed they went back over and tamped (sp?) It back level.. Has anyone tried this? If so how many bags would be used for a 10x10 area?

Paging Travis...

Hi Christina, welcome to Permies!

That description rings a bell for me, but I'm not certain where I saw it...  Was that video of the family in Arizona who built a bunch of Superadobe (continuous earthbag) cottages?  Could you post the video here?  If you get a link from Youtube or Vimeo, you can use the buttons to embed it.  

I'm very curious!  I'd like to see how it worked, held up, and what the ratios were.  If this method worked while only being tamped after being tilled (which it seems would mess up any tamping they did to the base first...?), that would be very interesting.  I would have thought that method would need to be mixed separately, then applied, leveled and tamped.  Rather than mixed in place.  Curious!

Your best bet might be to write them and ask how theirs turned out and how much cement or concrete (and what type specifically) they used and what soil composition they were working with.  And consider making some test plots first.  I've worked with a bunch of different types of concrete for somewhat unusual applications (flooring, wall covering, showers, and making gradients), and the test batches my husband and I did turned out incredibly valuable.  Sometimes it didn't behave the way we expected or were told it would.  This also allowed me to try out multiple different types of sealers and see what happened, too.  Like linseed oil versus tung oil versus walnut oil, that sort of thing.

In what sort of a structure are you considering installing an earth floor?  What will the structure be used for?

Phil Stevens wrote:Paging Travis...

Thanks...

Yes the technique is called "Earthcrete" and it works. Actually water is not even required because eventually the moisture in the soil will harden the cement/earth mix. Still, you can use water so that finishing the surface can be done nice and smoothly.

How much Portland cement you use (pure cement and not pre-mixed cement) depends on the strength. High strength concrete uses 5-6 bags to the cubic yard. For less strength you use 3-4 bags to the cubic yard. Myself, I use 5 bags to the cubic yard.

From here on out it is just math.

You never said how deep you want your concrete pad, but assuming 6 inches thick, I can do the math for you.

10'x 10' x 6 inch pad would be 50 cubic feet. Since there is 27 cubic feet in a cubic yard, you are looking at 1.8 cubic yards, so you will need (9) bags of Portland cement.
Now, Portland cement is getting harder and harder to find because few people mix their own anymore. But you will know it is what you want because Portland Cement is found in bags weighing 94 pounds. 80 pound bags are pre-mixed with gravel...you do not want that!

When I did my sheep farming classes, I talked about earthcrete a lot.

For concrete pads a person can just directly use the rototiller, but they could also use the rototiller for other applications. Like they could mix up the mix and then shovel the mixture into paper bags to stack up into concrete blocks. Again, due to moisture, the bags will eventually harden into concrete blocks. A person can let nature deteriorate the bags, or after they have hardened, light the paper on fire to get rid of it...assuming it is safe on many levels to due so.

But a person does not have to use gravel or earth, they can use sawdust for a light weight concrete, drywall powder for another lightweight inside concrete, or paper for a insulating concrete, etc.

I see people mix up cob a lot, and see them shoveling their guts out and wonder why they do not just mix it up on the ground with a rototiller? To me that would be a lot faster and easier, but I hate shoveling, and I do not know anything about cob, maybe a person has to mix it just so?

Question for Travis - how big can you go with this method before it wants to crack up a lot?  Could you do a garage floor over very sandy soil?  Can it support a car or SUV?

I want to build a Superadobe garage (vertical walls) as a test building for a future superadobe house.  I have been debating different options for the floor.  Superadobe bags on the floor is an option, but then it's lumpy unless you cover it.  And that is a lot more work.  I don't actually want to use concrete for ecological reasons...but we may want the floor in this building to cleanable, which makes concrete appealing.  We haven't decided if that's a necessity yet.

My husband and I were talking about just using a gravel floor and making a small concrete threshold for the garage door to seal against.  It's very important to us to make this garage mouse and rat proof, that's the prime reason for the garage.  Rodent-free vehicle storage.

Thoughts?

I like concrete only because I have a gravel pit, and for very little money can do a lot of projects with it. For instance my countertops are concrete, so the cost was $48 if I remember right. Most people think that it is slate. But the biggest reason is, I have a saying, "Do as much for yourself as you can, and so for me, making my own concrete is something I can do.

As for concrete...or any "crete" derivative, it is essential to know that concrete is made by a chemical process. For instance, if you take a bag of cement, throw it in a lake, in a few days it will be as hard as rock, even under the water. Again it is a chemical reaction.

So with strength, it is not the size of the pour, but how many bags of cement you have in the mix. A 10 bag mix...meaning (10) 94 pound bags of Portland cement to make a cubic yard of concrete is going to be really, really strong over that of a (5) bag mix. But a person could use nothing but Portland cement and water, and make concrete.

The reason gravel is typically used is that it is a strong filler. Broken as it is, it is consistent. What you are doing by adding the Portland cement in larger quantities (bags) you are adding more chemical to make the bond to the gravel better.

With Earthcrete this is a bit of a problem because it is not gravel...it is earth, so it is inconsistent. A person thus has two options for higher strength earthcrete:

1) Add more bags of Portland cement to counter the inconsistent soil that is being used. (Go with a 6 bag mix instead of a 4 bag mix as an example)
2) Use gravel instead of more cement

I do the latter because I have a gravel pit. But even if a person does not, buying a load of gravel is cheap and easy. Here anyway, I can buy a truckload (14 cubic yards) for $150. It does not take a big earthcrete pad to make buying gravel, cheaper then buying bags of Portland cement.

Additional strength in concrete can be had by adding rebar, which adds some tensile strength to it. However when using a rototiller, that is not possible because the tines would gnaw into the steel rebar mat. That limits how strong earthcrete can be, but for the most part it does not matter. Concrete in a concrete slab is pretty darn strong. I drove my bulldozer over my concrete floor in my barn without an issue. A BULLDOZER, pounding away on the 6 inch thick slab, and it never cracked...it never even marred the concrete's surface.

If you wanted too, a person could dig trenches and make a nice rubble-filled foundation with a concrete grade beam. That would be cheap and easy to do. Then a person could infill the inside of the grade beam with crushed rock or something. I have thought about doing that. That way in a few years if a person wanted a concrete floor, they could dig up a few inches of the rock and pour a concrete floor over it with no issues.

Is it rodent proof? In a word no, but is anything?

With some floors like wood, you get the rodents IN the wall, where they might get in and pull out insulation and cause cold spots. With a concrete slab, it forces the rodents to tunnel UNDER the slab. Either way, if a person has rodents, they have rodents, and must deal with them. And I will not lie to you, yes I have rodents too.

Of course a person could always go with a hybrid floor. Put down a modest 2 inch thick concrete slab to keep out radon, keep out the rodents, but then put a wood subfloor in, insulate, and then cover with sheathing and then a floor.

As for warmth, the rubble-filled/grade beam/ crushed rock floor would be the warmest. Earth lets the heat come up through because the ground is always 57 degrees. When it is 10 degrees outside, 57 degrees is warm! But a concrete floor is not as warm.

Myself, I prefer concrete slab floors. They are very energy efficient, and I am pretty sure Katie would divorce me if I ever tried to go with anything else. Warm in the winter, cool in the summer...what is not to love?

I love our concrete slab floors in the house we are in now, too.  The place we are moving to has brick floors over sand, probably doesn't keep out the radon, but it is working for rodents.  The walls of that house are concrete block, so that helps.  We are hard surface floor converts!  They are so nice and low care.  The brick one is harder to care for though, as it can't be as easily washed.  The bricks just sit on sand without grout.

I will clarify that "rodent-resistant" is my goal.  Living in the country all my life, wild rodents have been the bane of my cars' existence.  Right now we are in the desert SW without a garage and that is a huge packrat risk. My husband made a track of solar lights to park over top of.  Lighting the vehicle has been the most successful strategy for people in our area thus far.

Thanks for the ideas!  I hope the OP got her question answered...seems like it.

> rodents

Yeah, I sympathize. I recently developed something of a real attitude, in fact. <g>

They chew through light concrete; stones, gravel ditto. So do rodent research and likely use a strong concrete slab. To discourage rodents and provide dry, long lived walls, put garage walls on an 18" concrete stem wall.  Place the wall structure at the exterior edge of the stem. Cinder block works, but the voids can provide a wild life home/highway unless filled, and even then... Put a termite barrier on top the wall, then the PT wall plate. You can  retrofit these stem walls. BTDT, nothing particularly complex about it; in my case it was because of termite damage.

Putting the stem wall 24" into the earth on a footing discourages rodents taking up residence _under_ your slab. But 1-1/4 rock foundation, 18" wide 24"+ deep would do much the same. Beneath an enclosed garage stays about 40d or more which is really attractive to burrowers in cold winters or hot summers.

Detail everything with tight joints, including the roof at the top of the walls; caulk everything with _good_ caulk to discourage bugs and birds. Keep the edges of the roof in _very_ good repair. I favor closed eves to keep the surfaces simple to hose and blow clean. Keep 24" clear around the outside of the building. Walk the building once a month, try to spot any "interest" from mother nature. The more open and the more often people use a space, the less welcome to rodents. "Outside" cats and dogs help. Leaning material against the exterior walls for weeks, months, years is an open invitation to gnaw and enter...

Snap traps, checked regularly provide some warning if when there's instrusion.


Regards,
Rufus

Kim Goodwin wrote:I love our concrete slab floors in the house we are in now, too.  The place we are moving to has brick floors over sand, probably doesn't keep out the radon, but it is working for rodents.  The walls of that house are concrete clock, so that helps.  We are hard surface floor converts!  They are so nice and low care.  The brick one is harder to care for though, as it can't be as easily washed.  The bricks just sit on sand without grout.

I will clarify that "rodent-resistant" is my goal.  Living in the country all my life, wild rodents have been the bane of my cars' existence.  Right now we are in the desert SW without a garage and that is a huge packrat risk. My husband made a track of solar lights to park over top of.  Lighting the vehicle has been the most successful strategy for people in our area thus far.

Thanks for the ideas!  I hope the OP got her question answered...seems like it.

I am a convert as well.

I have only lived in (3) houses my whole life, and they are within 500 feet of each other. As I joke, I am moving south, but at Glacier Pace...517 feet in 26 years!

But last year we moved into a Tiny House that we have, and it had a basement, and was it ever cold. Now we are back into the big house again with concrete floors and it is amazing how much warmer this house is.

Last year I did not heat this home, and it was vacant while we tried to sell it, and the geothermal heat, as well as the super-insulation of this home, kept the heat to 44 degrees. That is not bad considering it was UNHEATED, UNOCCUPIED, and -7 degrees below zero (f) outside! It b=never went below freezing inside the house all winter.

But Rufus makes a good point. Where I live we do not have termites or poisonous snakes, so how we build is quite different from the rest of the country. For instance you could ride blindfolded across this country and know you were in New England in a second just from seeing houses with no gutters on them. As soon as you cross over from New York State into MA, the gutters are missing from the houses. Our winters knock them off in about a year.