Tips on a cement stabilized earthen floor?

Hi all

Im going to be pouring a small 10x12 pad for a shed and would like to mix native clay soil with cement. Has any one done this before? Tips on the procedure and mixture ratio?

Dear Sir,

Your posting said your building a "shed" ?

If the building will be exposed to the weather, a clay/sand/cement mix
is not a good choice for this use, because of the moisture it will be exposed to from open walls.

Now, conversely if your doing the "shed" like a home - closing it in as a dry building and raising the level of the finished floor above all possible rain levels, upon a proper moisture barrier & gravel base and again crafting the "shed" totally inside and out of the weather; then a 70% Sand, 25% Clay and 5% Portland Cement mix ( just like adobe or rammed earth mixes are made from ) should make a fine finished floor if installed properly.

The process is fairly widely published on the internet as well as on the Permies Green Building
Topic area, to give you the basic understanding of how to do it - just go do a small area , perhaps a dog house pad 1st , or something, just to get the feel of the work involved before starting a place you will be walking on for a several years to come and always work on your floors, in sections , with proper expansion joints, to separate the work spaces & your process so the finished sections will look uniform in their appearance . No reason to become over worked, due to trying to do a large pour, at one time all by yourself.

I hope that helps you some !
Happy Building !
Joe Woodall, Rogue Eco -Architect & Managing Partner
Georgia Adobe Rammed Earth & Renewable Energy

Location, location, location! portland added to earth will work well in dry warm climates, but in those climates earthern floors do not need cement. In my workings, portland added to earth/cob only helps against erosion and water damage-it does this well, but against freeze/thaw it does little if there's moisture in it.What's the climate in your location??

The building will be protected from the elements and is built a foot off the ground on a concrete stem well.
Im located in the San Francisco Bay Area, mild climate, doesn't freeze.

My ideal is to use the native clay on site and not bring in more material. Ive done a test before mixing the clay with cement and it came out well; was around a 4:1 ratio

My thought was that portland cement would create a harder floor (more damage resistant) and help it dry quicker

It sounds like you don't need portland, but if use use it, do 10-1 or less. 4-1 is a very rich  mix. I never go more than 6-1 in normal concrete. I've gotten very strong results at 15 or 20-1

I will be the first to admit I have no idea what I'm doing  Advice appreciated

I did read in a natural building book where they mixed vermiculite with cement in an 8:1 ratio

Bikemandan, Portland Cement (PC) will not give any advantage as far as keeping the floor dry.  PC loves to hold onto water and this is why it will mold.  The best material to use for keeping an earthern floor dry is Magnesium Phospate, which is more expensive than PC but at the ratios needed for an earthen floor, it could be do-able.  Check out www.geoswan.com if you would like to learn more about this material.

Thanks for the tip, I'll look into that

What about depth? 4"? Would it benefit from welded wire mesh like concrete?

Some type of reinforcement will be necessary to minimize cracking.  All concrete contractors I've talked to openly admit that all concrete cracks, to some degree.  Wire mesh and/or rebar help reduce this, as does proper curing.  One of the things that help concrete cure properly is to slow the process down. Keeping it moist does this.  Tarps and daily misting with water works though it is time consuming and work...but worth it if one wishes to have a quality floor.  Also, I have come across some information about wire mesh and rebar rusting and eventually weakening a concrete slab or foundation.  The alternative to metal reinforcement that I am aware of is fiberglass rebar.  It is claimed to actually be stronger than steel.  I don't know enough about it but you may want to do a google search.  I do know that it cannot be bent, in the field, the way that steel can.  Each application has to be pre-engineered to the specific requirements of a given job.  I have also read that the fiberglass rods have to be roughened up a bit before the pour in order to facilitate adhesion by the concrete.  I am about to (in the next month or so) have a concrete floor poured for a shop/garage.  For my living quarters though I am leaning heavily toward an earthern floor, or at least not a poured concrete floor.  I would like to have footings form the retention wall needed to contain a packed, washed gravel type subfloor and then use Magnesium Oxide or Mangesium Phosphate board placed over that.  Detractors would probably argue that this will be prone to shifiting and buckling of the Mag boards and they are probably correct.  There would probably be some shifting or buckling.  But I would rather deal with this than a cracking, rusting, Portland Cement floor that is prone to mold, and would have to be jackhammered if any of the plumbing encased in it failed.  At least with the model that I mentioned above, if any problems did develop I could pry individual Mag boards up and dig up the gravel without a jack hammer. 

Oh, I forgot to mention that, yes, my shop/garage will have a 4" depth concrete floor with rebar reinforcement.  The edges will be thickened to 6" and the piers that the I beams will sit on will be a full yard of concrete: three feet deep, and three feet square, from the plan view.

Also, no matter what you choose to use, it is good practice to use several inches of washed gravel, with no fines, as a base for drainage and also to use a vapor barrier (plastic sheeting at least 6 mil, the thicker the better) to keep your floor dry.  This is very important if you are going to use Portland Cement concrete.  It needs to be kept dry as possible once it has cured.