Ferro Cement

Thoughts on using this as a building material? How strong is it? How much of a snowload can it handle? Thinking of water reservoirs, small out buildings.....

Feral

here is a good ferrocement forum and site:  http://ferrocement.net/flist/index.php 
with good design ferrocement can be nearly equal in strength to steel plate in comparitive thicknesses. there are a lot of good ferrocement building sites for houses and structures. You might enjoy www.flyingconcrete.com
kent

I've done a little bit of ferrocement. It works well for certain applications. It is a lot of work and will almost certainly require a bit of trial and error before you embark on a big project if you have never done it.

It is heavy, generally easily repairable, and pretty easy to get leakproof. Even if you get a few hairline cracks, you can paint on a mixture of water and pure cement and get it to seal up.

The main thing to think about is that it gets most of its strength from its shape. In other words, it might work pretty well as a boat or water tank, but terrible as a flat roof since it would just sag and crack under its own weight.

On the downside, it takes a lot of reinforcing steel, and is labor intensive due largely to the time it takes to tie the reinforcing layers together and other prep work with the rebar/wire layers.

If I wanted to build a water holding tank, I would seriously consider it.

I appreciate your reply, love hearing from someone who's "dun it!"

Should I seriously consider... or reconsider?

I have found a few resources online about it. Currently I have a plastic water holding tank. I would like to increase the amount of water I'm able to store (fires.. etc).

Also how would it hold up in the winter? I'm assuming in freezing weather it would break, just like any other solid container left with water in it? (unless of course it was below ground!)

Thanks, Feral

Feral,
I'm not sure where you are, but freezing could be a concern. It will flex a little bit, but I don't think it would stretch.

Of course, you have the option to flare the sides a bit which should help keep it from bursting. You might also be able to make them corrugated or wavy allowing for a bit of bending.

Also, you could mix black coloring into your cement or paint the tank flat black to absorb the suns rays. Also, you could bury or earth berm the tank.

It seems to me to be a good choice for smallish to moderately large water tanks. If the tank were too large, it seems to me it would start to act more like a flat panel and loose a lot of it's strength particularly when it was empty.

Make sure you build it where you want it. If you are successful, and take care of it, it will be there for a long, long time.

Check out these pictures:
http://picasaweb.google.com/KeithDJPcA/FerrocementTankPix02#

It was done by these people:
http://www.permacultureactivist.net/design/Designconsult.html

I think there is an article on that tank somewhere.

In my opinion, ferrocement would only be suitable for outbuildings if you could put some shape in the walls for strength and if insulation was no concern or other wise provided.

It could probably work well for a pool or hot tub.

We're considering a ferro cement tank(s) for our main roof catch/potable water system.  However, due to the intense amount of labor involved, I can't help but think that an epdm (or something similar) pond/tank that was bermed to allow for it be above ground would be much more simple.  These tanks would be ~10,000 gal each.

lhtown wrote: You might also be able to make them corrugated or wavy allowing for a bit of bending....If the tank were too large, it seems to me it would start to act more like a flat panel and loose a lot of it's strength particularly when it was empty.

Ferrocement is strong if and when there is reinforcement aligned with any tensile forces that the structure might face.

So corrugation seems likely to cause failure IMHO, but the flattening-out you would see in a large tank wouldn't make the structure less strong against water pressure. The tank sees "hoop stress," and the appropriate orientation for a wire or bar to resist hoop stress is to follow the circumference of the tank, no matter how gradual the curve.

Joel,

Good point. I was thinking about strength against external forces like if a cow leans against it or a tractor backs into it or even wind forces. If it were full, it would likely still hold, a thin  tank would likely still hold against external forces thanks to the internal water pressure, but it could be easily damaged if it were empty. You are right that corrugations of the side wall would be worse than worthless against internal water pressure. Of course, you could always make the walls thicker, but then you have poured or cast concrete instead of ferrocement!

Also, corrugations of the side wall might allow for some flexing in the event of a hard freeze that a round tank wouldn't.

All in all, we are talking theory here about the corrugations, and I really can't imagine doing it. They seem to only be practical in situations for which ferrocement isn't practical. An exception might be a barrier wall, but that isn't what we are talking about here.

In any event, my greater point is that thin flat ferrocement walls are very weak under regular stresses. For example, you could make something like a bathtub out of ferrocement that was only maybe 3/4" thick or even thinner with very good technique. A square box of similar size would with the same wall thicknesses would be a disaster with the walls bowing outward and cracking under the weight of the internal water weight. You might have to make the cement over an inch thick and still add support at strategic locations.

Southeastfarmer,

In my humble guestimation, if there ever were a size of tank that was ideal for ferrocement, it would be in the 10,000 gallon gallon range.

Just sitting here thinking about it without ever having done a tank over about 300 gallons, it seems like a tank with a diameter of maybe 5' to about 25' would be the most ideal for ferrocement construction.

I'm learning more and more about ferro cement. I may end up not liking it because it may be too labor intensive... and I'm LAZY!!! however, I also tend to enjoy and find relaxing things that are repetitive, so it may be just the thing for me, I'll have to try it!

For those experienced with Ferrocement:

I use Zeer Pots to cool food with in the summer. Is unsealed ferrocement porous enough to where a ferrocement container could be utilized for a big zeer pot?

Feral

Feral wrote:I use Zeer Pots to cool food with in the summer. Is unsealed ferrocement porous enough to where a ferrocement container could be utilized for a big zeer pot?

Still only talking theory here, but I'd worry about corrosion.

It's important to have a good barrier between carbon steel and the elements. In most concrete, this is a thick layer of cement & aggregate. I believe with ferrocement, the strategy is to seal more carefully, so as to get away with a thinner layer.

If it's porous enough to wick out a constant supply of water, dissolved substances will be carried along with. That include ions dissolved from the material itself, potentially including minerals that would have protected against corrosion, or iron ions themselves. It will likely be obvious as rust stains before it destroys the structure, but I would hesitate to risk it.

Normally ferrocement is impervious to water. Sometimes hairline cracks will develop when it dried, but they won't generally leak. Normally ferrocement is completely waterproof without any kind of treatment or coating. In any event, small cracks can be sealed up in a new construction by mixing some cement with water and painting it on.

If you wanted to make it porous, you would probably have to use an aggregate that would impart that property. Joel makes a good point about the wire rusting. You would probably want to use something besides galvanized steel for reinforcement.

If you are really into it, search around for papercrete and let us know if you come up with anything. I can't imagine much reason to mix the two technologies, but they are both fascinating.

I've never built a ferrocrete structure, but I read a really enjoyable book by Art Ludwig on the subject a few months back:

Water Storage: Tanks, Cisterns, Aquifers, and Ponds
For Domestic Supply, Fire and Emergency Use
Includes How to Make Ferrocement Water Tanks

http://www.oasisdesign.net/water/storage/


I got it from the library, but once I get some cash flowing in, I plan on purchasing it, as it is chock full of good information.

lhtown wrote:
If you are really into it, search around for papercrete and let us know if you come up with anything. I can't imagine much reason to mix the two technologies, but they are both fascinating.

If I can answer my own post... I thought of a reason to mix papercrete and ferrocement. I think it could have a practical application in making an insulated holding tank. Make the liner of ferrocement, form up papercrete around it to the desired thickeness and if you need a more durable outer shell, tack on a couple of layers of chicken wire and ferrocement the outside.

Oh, and if anyone tries it, post back and let us know if it actually works...

Glad to see the recommendation for the Ludwig book. It's on my "to order" list.

If I go ahead with a ferrocement reservoir next year, I think I'll stick with the plain ferrocement initially.  I can see where the papercrete may be insulating and that would be a good thing where I live at. So... we'll see what next year brings! I've got too many projects to try it this year.

Following up:

I think the best gigantic zeer pot might have a ferrocement frame, with windows of something more porous that hold the sand in but allow water to pass.

I've never worked with Ferro Cement.  Suppose one wanted to build domes or barrel vaults.  Do you think Ferro Cement might be superior to other types of form work?

The magic of domes and barrel vaults is that a good design might potentially eliminate any tensile load on the material. They can be built from masonry with no reinforcement.

The distinguishing characteristic of ferrocement is the high fraction of reinforcement used. Typically, so much steel is used that  gravel is eliminated from the concrete recipe. This large proportion of reinforcement gives tensile strength beyond what one would expect of masonry; properties more like one would expect of a brittle metallic material.

Boats and water tanks (unless they're shaped like dams) need to handle tensile forces, but I think it's usually better to design your masonry structures so as to avoid that need, or to have a moderate-enough amount of tension that only reasonable quantities of steel are necessary.

I've done a lot with ferrocement, including vaults, domes, water tanks, buried homes, etc.

One thing I can tell you is that IT IS NOT WATERPROOF.  That's right folks, it will leak, or at least, seap.  But, depending on the water source, the leaking can actually cure itself, as minerals get deposited in the cracks/pores, and the leak eventually stops.

To make it completely water proof, you need a final coating of Thoroseal or just cement, water, and acrylic.

Very fine sand and/or fly ash helps with the waterproof issue.

Cold joins are the biggest problem with water tanks, you need to reduce them as much as possible. 

Mangudai wrote:
I've never worked with Ferro Cement.  Suppose one wanted to build domes or barrel vaults.  Do you think Ferro Cement might be superior to other types of form work?

The magic of domes and barrel vaults is that a good design might potentially eliminate any tensile load on the material. They can be built from masonry with no reinforcement.

In order to pour wet concrete into an arch a formwork is necessary.  I was wondering if ferro cement could handle the weight of all that wet concrete, and if this is better (simpler, cheaper) than a temporary wooden form. 

Ferro-cement could take the weight of the wet concrete, for sure.  BUT, if you have ferro-cement there already, why are you pouring concrete on top?

Here's some good info for formwork:
http://www.flyingconcrete.com/movableform.htm

http://www.flyingconcrete.com/vreinforc.htm


Formwork doesn't have to be made of wood, it can be mesh covered with old tarps or anything else.

I've used cheap builder's plastic as formwork many times.  It works great.

Some folks even use inflatable formwork.

velacreations wrote:
I've done a lot with ferrocement, including vaults, domes, water tanks, buried homes, etc.

One thing I can tell you is that IT IS NOT WATERPROOF.  That's right folks, it will leak, or at least, seap.  But, depending on the water source, the leaking can actually cure itself, as minerals get deposited in the cracks/pores, and the leak eventually stops.

To make it completely water proof, you need a final coating of Thoroseal or just cement, water, and acrylic.

Very fine sand and/or fly ash helps with the waterproof issue.

Cold joins are the biggest problem with water tanks, you need to reduce them as much as possible. 

You usually don't "poor" concrete in ferro-cement.

That being said, I have done it.  I wanted a thicker more insulated wall.  The frame is wire, vertical, 6 inches thick.  The frame is covered in burlap soaked concrete and acrylic mix, weaved in and out with wire (free) to hold burlap on and give it more strength.  Wire also used across the 6 inch width to hold the sides together.  This then gets filled with a mixture of recycled foam (peanuts and packing  foam) and concrete mix....and a few beverage cans .

Ferro-cement is usually thin.  it is stucco'd not pored.

It is labor intensive, but I love it.  The hands will burn and peel if you don't wear gloves. 

pores, as in small holes.

You don't want the concrete very thick on ferrocement, the reinforcement is best utilized when it is within an inch of the surface of the concrete.

Laminated ferrocement can be a big improvement on quality, mostly because you put the mesh into the mud, instead of the mud into the mesh.  So, you avoid small cavities, "pores", or other imperfections that you get when you apply the mix to the mesh.

What you really want is a panelized system, like what they use in India:
http://ferrocement.net/flist/index.php?topic=126.0


They make small forms, pour a stable, thin panel, cure it well, and then place it on the building.  It comes out cheap, quick, transportable, and much more durable than metal.

If you are interested in Ferrocement, be sure to read
http://ferrocement.net/

We've done a lot of ferro-cement, especially for roofs. The Ferro-Cement discussion list mentioned above is a very good resource. We did our house's barrel vault roof with ferro-cement. See:

http://flashweb.com/blog/2006/12/first-layer-of-roof-on.html
http://flashweb.com/blog/2006/11/taming-trusses.html

http://flashweb.com/blog/2006/12/inner-scaffold-down.html

Also see our dog house:

http://flashweb.com/blog/2007/09/dog-house-bottles-roof.html

We've done other animal shelters and things with it. Currently we're working on building a ~40'x40' on-farm slaughterhouse and butcher shop which will a have ferro-cement roof. For our cottage we hand lifted 1.5 cu-yds (6,000 lbs) of in buckets up a ladder to the roof. This produced a 1.5" thick roof. For the slaughterhouse we'll use a pump truck!

Cheers,

-Walter
Sugar Mtn Farm
in Vermont

I built a ferrocement koi pond 10 years ago, it works great, holds water and has a nice patina on it now that looks beautiful.  I would advise spending some time building a sturdy frame, and making sure that you apply your cement mixture in even layers to prevent cracking.

You might enjoy this site:  http://www.shambhalavillage.com/   They are buiding almost exclusively with ferrocement.  They have a number of interesting videos, as well.

pubwvj wrote:
We've done a lot of ferro-cement, especially for roofs. The Ferro-Cement discussion list mentioned above is a very good resource. We.....

-Walter
Sugar Mtn Farm
in Vermont

Nice.
That is a LOT of work. I am impressed.

-------
For the others...
I also want to add that when you apply the ferocement with a trowel you work it.
You push and pull at the trowel and it moves back and forth and then suddenly it goes smooth. When it does this, a layer of wetness forms on the surface.

It will still crack if your mix has too much water in it, but there is this kind of internal change that takes place when it is finished.

jeanna

Thanks for your generosity in sharing your information with the world wide web.  I happened upon your posts, and feel that they've changed my life!  Well, we'll see after I make the first real ferrocement structure, but there is real hope now for sure.  Current plan is to make an Earth Bag house with ferrocement on the outside of it.  The ferrocement appears to compensate for any building code problems that the Earth Bag structure would otherwise have because of its terrific strength.  We will unfortunately have to build it to code as our lot is within county limits, but the ferrocement is what will make the Earth Bags possible.

My family and I have always had housing problems for whatever reason like all of the other Americans( foreclosures, evictions), and the ability to use ferrocement for making a house of our own will really change everything for us. 

I went to ferrocement.com and spent about $28.00 at Home Depot for some Portland Cement, sand, and wire mesh.  They also sell 12 inch rebar so you can make a model ferrocement house to see how the material works and what it can do.  Hubby and I made a sample foundation and roof using wire mesh, burlap, and ferrocement over it.  We stuck the rebar into our mini foundation to see how it stood up and followed the curing process for the last 24 hours.  It is really hard!  We are amazed!  Can't wait to see what will happen in a couple weeks. 

Keep up the good work with the posts.  We will be watching for more!

I have read some posts that folks think that the ferro cement structures will last thousands of years and others seem to think that metal in cement will rust and cause the cement to break up... so how old is the oldest ferro cement structures and how long do they last?

I don't want to build something and then have to rebuild in a few years.

there are at least a few ferrocement boats that are many decades old.

There are ferrocement boats that were built in the mid-1800's that are still in excellent condition. Ferrocement lasts. Those were old style. Modern ferrocement utilizes more advanced techniques and materials that were learned from the mistakes of the last 150 years so the new stuff is even better. There are additives to the cement that make it more waterproof, self healing, reduces oxidization, new fibers that last better than steel, improved application techniques.

Additionally, don't limit yourself to just ferrocement. We used a variety of masonry techniques from stone work to steel reinforced concrete to ferrocement to brickwork.

Thanks. What type of cement is it that has the qualities you mention? What type of steel is best to use?

ronie wrote:
Thanks. What type of cement is it that has the qualities you mention? What type of steel is best to use?

Unfortunately the question is too complicated to answer in detail here but here's some things to look into:

Start by learning about cement.
Note that cement is not concrete.
Concrete is a cement binder with or with out additives used to bind together aggregate.
Concrete by weight has very little cement and is mostly stone.
Ferrocement has little stone, but rather sand and more steel than RC (steel Reinforced Concrete).

Then there are additives. There are a LOT of additives. Starting with the old time volcanic ashes and onward. These harden cement faster or slower, stronger or weaker, air entrain it, waterproof it or make it otherwise behave differently.

Then there are reinforcing materials such as steel, glass, resins, polymers rods, meshes and fibers that give tensile strength to the concrete. Remember that concrete is a compression strong material.

Then there are coatings such as epoxies, fiberglass and such that are used with concrete.

Then there is the shaping to optimize the structural elements. Thing arches, vaults, beams, trusses, decks, etc.

Well, that was concrete 101, page one intro.
Google those topics and start reading. Enjoy!

One of the things I'm working on that is intimately related to all of this is how to put our very cold winters into a bottle so I can drink that cold all the year. Well, not drink but rather use it to cool our 736 sq-ft walk in cooler for our new on-farm butcher shop. Electrical usage for chilling and storage is a big cost. Since we're building from scratch we're doing some interesting things to bottle winter. After it has been running for a few years I'll write up results.

Cheers

-Walter
Sugar Mountain Farm
Pastured Pigs, Sheep & Kids
in the mountains of Vermont
Read about our on-farm butcher shop project:
http://SugarMtnFarm.com/butchershop
http://SugarMtnFarm.com/csa

Walter, are you going to build a pop bottle icehouse, as described a few months ago?

Muzhik wrote:
Walter, are you going to build a pop bottle icehouse, as described a few months ago?

I think I know the reference you mean. Same sort of idea except we're using much larger containers. We have a much larger BTU load to deal with since there are fresh carcasses coming into the chill room each week. I doubt I'll be able to use it to supply all of our needs so we're going to be doing several different methods in parallel all backed up by modern, efficient electric based refrigeration which will eventually be run off of our own micro-hydro. Additionally we're taking the heat on the other side of the system and using it to preheat our hot water and administrative portion of the facility. Waste not, want not.

Where did you see me confuse concrete and cement? I know what a vault is and the value of an arch for strength.


I was hoping to get some input from someone that has experience with ferro cement that could tell me what they used as additives and what their experiences have been. If they would do it the same way again or do something different.

I was also hoping that those who have had bad experience with ferro cement would chime in with what not to do.

Also would like to hear from those who have been saying that steel in cement is not good and why they think this and if this applies to ferro cement as well.

We've done a lot of ferrocement. We don't really use many additives, but a few are worth mentioning:

Fly Ash - you can substitute a bit of cement with this.  It is super fine and really helps with water penetration.  Usually like 5% per mix, though some folks substitute up to 50% of their cement.

Acrylic - this is great for water proofing and really helping with flexibility.  Replace up to 50% of the water in a mix for a super sticky, really nice mix.  This will adhere well to even old concrete (cold bond).

Mesh - I like layering different sizes of mesh, down to something very fine.  Nylon is good, but for the main, base layer galvanized is good.  I usually go rebar, remesh, galvanized lathing, then nylon screen.

Neat cement - mix cement, water, and a bit of acrylic to a paint-like consistency.  Paint this on as the final coat for exteriors.  I like to paint it on after the wall has cured for a few weeks - months.  It helps with small cracks and filling voids.

Tools - If you can get a mortar sprayer, it makes things go faster.  For mesh, use hog ring clamps and pneumatic pliers.  You're armature/mesh eats at least 70% of your time, so get fast at tying things together.

velacreations wrote:
We've done a lot of ferrocement. We don't really use many additives, but a few are worth mentioning:

Fly Ash - you can substitute a bit of cement with this.  It is super fine and really helps with water penetration.  Usually like 5% per mix, though some folks substitute up to 50% of their cement.

Acrylic - this is great for water proofing and really helping with flexibility.  Replace up to 50% of the water in a mix for a super sticky, really nice mix.  This will adhere well to even old concrete (cold bond).

Mesh - I like layering different sizes of mesh, down to something very fine.  Nylon is good, but for the main, base layer galvanized is good.  I usually go rebar, remesh, galvanized lathing, then nylon screen.

Neat cement - mix cement, water, and a bit of acrylic to a paint-like consistency.  Paint this on as the final coat for exteriors.  I like to paint it on after the wall has cured for a few weeks - months.  It helps with small cracks and filling voids.

Tools - If you can get a mortar sprayer, it makes things go faster.  For mesh, use hog ring clamps and pneumatic pliers.  You're armature/mesh eats at least 70% of your time, so get fast at tying things together.

Thank-you Vela, I have read many of your posts, but my old mind doesn't remember much anymore. Do you usually use a 3-5 sand to portland mix? Are you saying that you use 5% fly ash to 95% sand portland? or 5% portland sand to 95% fly ash? I don't even know where to get fly ash...is it something that is easy to come by?

Have you done any underground vaults or cisterns?

SO when you layer mesh and lathe and screen do you apply a layer of cement/sand mix then add more metal lathe/mesh and then add more cement? Or just put up the rebar and all the metal at once and then spray or tool on the cement mix?

3:1 sharp sand to cement.  5% of the cement as flyash.  You can find flash wherever there are coal power plants.  It is easy to come by once you find a source.  They'll give it to you by the ton!

I have done partially buried vaults and semi-domes.  No cisterns... yet.

I usually put up all the rebar, remesh, and lathing (no nylon screen) first, then hand apply or spray the stucco (sand/cement) in 1/8" layers.  On the final layer, I either put in fibers or nylon mesh, pressed into the stucco.  After it has been set up for while, I then paint the neat cement on last to smooth things out and really seal it up.

Thanks Vela, I think I'll go look around your site - it looks like you have done quite a lot of projects and your site is pretty amazing as well.