This low-cost floor idea goes back to India and the writing of Ken Kern. CountryPlans Admin Glenn Kangiser has further developed and experimented with this system in his Sierra underground home. Here is a new report where we consolidate this information into a web page: Plunger Pile Floor System

Please use this thread for questions and comments.

This really looks interesting.  It's hard to believe that so little cement will be so strong.  It seems counter-intuitive.  We're told that we have to build everything bigger and stronger and thicker with more and more rebar.  Amazing that this works.

I'm not really clear about the cement material that you are using.  In one place you describe it as mortar/stucco and others cement and sand.  Not being that familiar with cement work I'm not sure what if any difference there is.  Could you clarify?  

When using pilings is it the same mixture?  And how big are those holes (diameter)?

I was thinking of building a small pond in my yard.  I wanted to built it out of concrete (I hate how this EPDM liners look).  I wonder if this system would work for that.  I'd probably have to cover the surface with surface bonding cement to seal it though.  I could also go much thicker than 1/2 or 1".

I think fiber reinforced concrete has some great potential as a new composite material that, much like carbon fiber in aircraft, can combine great strength, light weight and surprising flexibility. That it can be worked up with simple tools and materials should mean lots of interesting experiments.

I will let Glenn speak to the other good questions.

Thanks, John.

Quote from: archimedes on February 17, 2011, 06:29:45 PM
This really looks interesting.  It's hard to believe that so little cement will be so strong.  It seems counter-intuitive.  We're told that we have to build everything bigger and stronger and thicker with more and more rebar.  Amazing that this works.

I'm not really clear about the cement material that you are using.  In one place you describe it as mortar/stucco and others cement and sand.  Not being that familiar with cement work I'm not sure what if any difference there is.  Could you clarify?  

When using pilings is it the same mixture?  And how big are those holes (diameter)?

I was thinking of building a small pond in my yard.  I wanted to built it out of concrete (I hate how this EPDM liners look).  I wonder if this system would work for that.  I'd probably have to cover the surface with surface bonding cement to seal it though.  I could also go much thicker than 1/2 or 1".

Ken Kern discovered this floor in India where the people are too poor to waste resources and often they experiment with cheaper but still durable technology.

Concrete easily reaches a compressive strength of 2500 PSI but many times especially with cement  rich mixtures it reaches much more that in it's normal complete cure time of 28 days (It can cure for a lifetime actually but the major curing is complete in 28 days  - code work allowed in 7 days).  Reinforcement of steel or other fiber gives it tensile strength keeping it from pulling apart.  Concrete without reinforcement may crack and separate.  

The cement in concrete readily attaches to the jute, hessian, burlap or fibermesh making it a strong composite material somewhat on the order of fiberglass.  One piece of reinforcing fiber may take 50 or a hundred pounds to break it... multiply that times hundreds or thousands and that gives you an idea of where the strength of this material is achieved.

The US military successfully experimented with bamboo reinforcement in concrete for bridges though they did use special procedures.  They have also built house shells spanning wide areas in India using similar techniques and materials.

A tractor can easily sit on a 4 inch concrete floor.  As an example, a human or a bunch of them no where near reach the weight of a tractor.  

Cheap but good low tech methods do not sell lots of materials or increase the tax base, hence you will not hear any of this from domestic sources in the US.  

My use of different terms is just an effort to get people to understand what the material is.  Since it is not in common use in the US few understand the concept or materials.  Stucco is about the nearest thing we commonly use in the US that is similar to this floor, but it is sand and cement with some lime used over a steel wire or mesh reinforcement.

In my experimenting with this material I find that the steel mesh or chicken wire as used in stucco does not perform as well as the jute reinforcement.  Don't limit steel out - it may have it's place in one of your projects or is great in ferrocrete and stucco, but for the floors the jute performs best,  The steel likes to poke up and spring back when you trowel the sand/cement mix onto it.  Wetting the jute makes it lay flat and readily bond with the cement in the sand/cement mix.

Stucco is a sand, cement, lime mix used for concrete walls on buildings in a lot of California and other places, and was invented in Rome around 2000 years ago as I recall.

Note Kern first mentions that the floor is 1" thick, but in another couple sentences he mentions that it is a lightly reinforced concrete floor consisting of two layers of concrete 1/4 inch thick --- total actually, not including the sand below it is 1/2 inch concrete.  I find that the 1/2 inch is sufficient with the jute reinforcement and especially if Fibermesh is added.  Even if you go 1 inch - you are saving 75% over a 4 inch floor.

Clarification on the concrete.  I hesitated to call it concrete because most think of concrete as having rock.  It is not really mortar or stucco as they usually contain lime making it too soft and weak for this application.  It really is a concrete but no aggregate bigger than sand is used.  That is why we use the cement rich mix of 1 cement to 3 sand (Not specified by Kern that I noticed - found by my experimentation). Sand is rock, - just very small rock.   Kern touched on a lot of things but did not always go into great detail on some of it.  There is more to glue together than if there are rocks in it, so I richened the mix.  Possibly less cement would do upon further experimentation but I am happy with that mix.

I use the same mixture for grouting the pilings, usually making the holes through the jute reinforcement then filling the holes before putting the first layer on top of the jute.  You could experiment with filling the piers before applying the jute but it works for me.  I just knock the top level with a wood float if I mess up the sand.

I have successfully used holes of varying depth to even no holes on hard ground or soft ground where I wanted the patio floor to just follow the ground if it settled around the above ground pool.  I was interested in drainage there anyway.

I use a post hole digging bar with about a 3/4" to 1" end and repeatedly forcefully hit the same spot with it until I reach undisturbed soil then fill the hole with grout.  I usually do about an 80 square foot area at a time sometimes putting permanent wood partitions in to level with.  That is not essential though.  

I would try this method for the pond though you might want to change to chicken wire (usually 3 or 4 layers wired together against the sides of the pond in the shape you want) and a bit thicker for it due to possibly having a bit more moisture and possibly rotting the jute. The jute is cheap and you could put a layer of it against the ground as a separation from the soil and additional reinforcement.  I use a rubber tile grout trowel for irregular surfaces - the slick flexible black ones - not the spongy ones.

Fibermesh could be used and will not rot as it is a type of poly fiber.  Fibermesh makes it easier to plaster with.  Using the multiple layers of chicken wire makes it into ferrocrete.  I have been told neat cement will seal it (cement powder and water to make a paste).  Even thicker cement will leak without a sealer.  

Sani-tred, Thoroseal or Moxie all make sealers, though it will likely not leak enough to worry about and it will eventually pretty well seal with algae and other materials.  Rinse it out with vinegar water - remove it then put fresh water before putting plants or fish in it.  Concrete is highly alkaline when first poured or plastered.

I have successfully instructed others on making a 400 gallon septic tank effluent reservoir from ferrocrete and the county approved it.  It has worked several years with no problem.  Actually it was a lady who built the tank as she wanted to learn to make the ferrocrete herself.

Texas Tornado posted an interesting thread with a video on a shell building using alternative reinforcement.

http://countryplans.com/smf/index.php?topic=10295.new#new

I really like the patio, Glenn



I saw this link posted here and wondered if the Basalt Roving would work in place of the jute for reinforcment

The price is sure affordable


http://www.monolithic.com/stories/monolithic-ecoshell-built-with-basalt-roving

Thanks, Windpower.

I have searched in vain for a reasonable priced supply of Basalt roving.  I only found one place with a price of $5 per lb.

I will be looking for the material at a reasonable price if anyone finds it.

In the meantime, I have read of the people in India using the Jute reinforcement for very wide shells for houses.  In the air I would not worry about decomposition of the jute especially if the shell was waterproofed on the outside.  

They built temporary frames, wet the jute and stretched it to tension it snugly then applied the cement allowing it to cure.  Seems theirs was more like burlap or hessian.  

For those who want to try, As always... use extreme safety with experimentation so you will live to experiment another day.

For those who didn't follow John's links above here is one pix from the pool patio info



and a lot more info about how the floating pier-less pool patio floor was done  here....

http://countryplans.com/smf/index.php?topic=151.msg62452#msg62452

I'll try to locate more links to my other experiments later.

Lost forum discussion from the very old forum I found on the Wayback Machine.

http://web.archive.org/web/20041022004957/countryplans.com/bbs/messages/7250.html

Glen,

I'd be interested to here how you constructed the septic tank?  No rebar?

How think was the concrete on that?  How did you connect the walls to the bottom and the lid?

I can only imagine how the permitting people were scratching their heads.   

This was just an effluent holding tank to put the lift pump into though the septic tank could be done that way too with proper holes - baffles etc.

I supplied the knowledge and the lady client supplied the manpower.... I mean, woman-power....

First I dug a hole big enough for the desired capacity -roughed out with the backhoe - around 400 gallons as I recall.  She then rounded the hole to shape and smoothed the bottom.

After that several layers of chicken wire - 3 or 4 were cut to fit the bottom and rolled to diameter to fit the sides the tied tightly together with wire in many places to hold the shape.  It was fit snugly to the inside of the hole.  Heavier 6-6-10-10 could be used as an armature frame if desired.

Next a concrete plaster was made similar to the above floor mix.  About 1 cement to 3 plaster sand.  Fibermesh added to this mix will be beneficial to help grab the wires and reinforce it.  It is plastered on with a swimming pool trowel or or rubber grout float --- or whatever tool you may prefer to those.  There are plaster sprayer plans online that would work great with this too.  

A good method is harling -- Al should know a bit about that - it is a Scottish method of throwing the plaster into place, that sends it through the wire and makes it stick to it.  It is not imperative to cover everything on the first coat.  Things will firm up the second day and another coat can be applied.  Trowel enough to get the concrete plaster to go through the wire and a bit out the other side.  As it hardens the wire will become entrapped and reinforce the tank in all directions.

She continued adding layers of cement plaster until the wires were all encased and the inside was smoothed into a very nice looking tank.

We molded the top on the ground with a lid with angled edges spaced out with 1x4 wood right in the tank top, but it was taller than the tank top so it could have the wood removed and sit into the hole without falling in.  Chicken wire was used in the top as well as some rebar around the perimeter and through the top for strength and also some for lifting it were added.  I set the top in place with my crane truck and she plastered it on from the inside.  

The opening was a manhole size so the pump could be put in and serviced.  An extra outlet was put in the side for the uphill effluent line and for electrical wiring.

Surprisingly the health official was happy with whatever we made as long as it did not leak.

This would be considered ferrocrete and I think we had some other discussion on it a long time ago.

Since water can be very heavy,  how thick would you guess the walls were?  Was any add'l waterproofing used in this application?

Very interesting, thanks

The walls were not over 1 inch thick except where there were irregularities in the digging of the hole.

The chicken wire provides the tensile strength - steel is average 50000 psi tensile strength.  The concrete is roughly 2500- 3000 psi compressive strength.

If we have an average of 4 wires per inch at 50 lbs each that is 200 lbs tensile strength per inch or about 2400 lbs per foot.

Water has a pressure of .433 lbs per square inch per foot of head or 2.31 feet per lb.  A 4.62 foot tall tank would have 2 psi at the bottom, well covered by the strength of our reinforcing wire.  As tanks get taller and bigger more reinforcement can be added but you could build any size tank you desired.

Note that we did not add any sealer to this tank as we were trying to get rid of the water anyway, so a bit of dampness passing through was not a problem and likely it would seal up after a short time anyway.

Here is a link to one of my earlier experiments with the CBRI floor where I used aviary netting - steel small chicken wire for reinforcement.  I was not as happy with the performance of this wire as I was with the jute netting.  It did not seem as strong and as I mentioned before, the wire does not like to stay down as well as the jute.

http://countryplans.com/smf/index.php?topic=151.msg7536#msg7536

Note that it starts there then skips up a couple pages for the finish of that experiment.

Here is the second half of the story.

http://countryplans.com/smf/index.php?topic=151.msg8269#msg8269

That floor is still there and working today but I think I may not have had the mix rich enough - there was a little bit of spalling.  Easily and cheaply repaired though if I want to.

Great report Glenn. That was over 5 years ago.

Thanks, John.

Sassy agreed that I may have cut down a bit on the cement in the mix at the time causing the spalling.  

Here is another one I did in the master bathroom.  This one has piers that are up to 18 inches or more deep under the bathtub only.  We have the same floor in the rest of the bathroom but it was done earlier as we had planned on putting a shower in there.

The floor is still flawless, but there is one thing I don't like about it.  I tried to make it look like stone work under the tub shaping sections into individual stones with the edger and trowel.  This leaves places that are much harder to clean requiring vacuuming or wet mopping once in a while.  We have settled on the smooth floor with the color variations  rather than physical edges and separations due to the greater ease of cleaning.

For more of the story and other pix see here.

http://countryplans.com/smf/index.php?topic=151.msg21571#msg21571



The rocking chair is on the older part of the CBRI floor.

Interesting stuff Glenn.  thanks for posting

An old time concrete guy once told me that spalling is usually caused by too much water in the mix.  I don't know if it's true or not (don't have enough personal experience)  but that's what he told me.  He seemed like he knew his stuff though.

Could be that I added too much when troweling the top smooth too.

How has the Basalt roving changed over the years, price-wise? Is that still what you recommend for newer projects, or is there something else that's come out that you now like better?

Thinking that I could start playing with this even in the city, maybe make a patio out back? I don't plan to drive any tractors around in my 1/6 acre back yard... 

Leif