Ferro-Cement

My experience with ferro-cement started as a young man, by reading about how to build ferro-cement boats. The idea of using chicken wire and cement construction is not at all new. The old timers called houses with this type of construction "Chicken wire & cement houses", which pretty well described them. The main difference between the old "Chicken wire" walls and the "ferro-cement" is the amount of chicken wire used. In the old type of construction, only one layer of chicken wire was used and this was just to hold the cement to the side of the wall. With ferro-cement, 2 to 5 layers of 1 inch mesh chicken wire are used, depending on where they are being used and what strength is required. Cement is the strongest when it is less than one-forth of an inch away from steel reinforcing. In ferro-cement, the overlapped chicken wire is the reinforcing, and all of this wire is what gives it its great strength and ability to withstand stress. By having several layers of chicken wire, with the cement being forced to fill in all the spaces, a very strong cement structure is the result.

If this is sounding pretty simple, it's because it is simple...but it works. There are many ferro-cement boats, still in service that are over 50 years old. Think of the stresses these boats have to endure while on the high seas. Hopefully your house or barn will never be subjected to this kind of stress. If it ever is, I don't want to be in your neighborhood! If the use of chicken wire and cement for outside walls has been around for such a long time, how well does it hold up? Even with one layer of wire, the walls work well. Many walls never had any sort of "sealer" applied and many were never even painted, and yet most lasted for as long as the house was used. Many did develop cracks and had to be repaired from time to time, however. This was not due to flaws in the cement work, but from the house settling as it aged.

While we were paying off our land in Florida, we had very little money for building. We managed to get enough 2x4 s and 2x6 s to put up a shell of a room and we got plywood for the roof and a neighbor gave us some asphalt roofing. At this point we had very little money left and could afford only "tar paper" to cover the outside walls. We literally had a "tar paper shack". We looked into plywood and siding for the walls, but both were too expensive. Northern Florida is not "blessed" with building stone and most of the trees on our land are too small for log construction. The soil here is almost all old beach sand and unsuitable for adobe. Did I say beach sand? Sand like you mix 4 to 1 with "Portland cement"? ;) There was our answer, right under our feet all the time. We had some 1 inch chicken wire already, so we attached it to a part of the wall (leaving the wire out just a bit from the wall, so that the cement could get behind the wire) and mixed up a couple of wheel barrels of cement and forced it into the wire. The cement held fast to the wall and was pretty easy to put on.

The next two days, we waited to see how this was going to work. Many of the old "chicken wire" houses had boards behind the wire for support, but all ours had was the tar paper. Once the cement had well set up, I put it to the test. I hit the wall between the studs with my fist, and then drove several nails into the cement, to see if it was likely to crack or break. My wife and I were both impressed with the strength of the work that we had done, so we continued to cement the wall. We later got to test these walls in hurricane "Opal's" winds and they held up just fine.

Our next ferro-cement project was a water storage tank--possible "hot tub"--in our "plant starting room". The idea was not only to have water storage, but by the water heating up during the day, it would help keep the potting room above freezing at night. I laid down several layers of chicken wire on a section of cleaned ground (sand), for the bottom and foundation of our tank. I turned the edges of the wire up and filled the bottom with cement. Once this had set up I came up with several layers of wire and filled this with cement. We then painted the finished tank with pool paint and it has held water ever since. It holds about 500 gallons, is plumbed for turning it into a hot tub, and has a drain at one end.

We were not keeping good records at the time, but we guess that the whole thing, including the pool paint, but not counting my labor, cost us less than $ 50.00. I went ahead and put the pipes into the tank, in case we ever want to turn it into a hot tub, because otherwise, making holes for them would be next to impossible once it was set up. For those interested, the wire on the bottom is 5 layers (I did not want any cracking), and the wire on the sides is 4 layers. I could have used less on the sides, but I was building the tank-pool more or less "free form" and needed the wire to keep the cement in place. Our tank is irregular shaped, 2.5 foot deep and about 6 foot by 4 foot in size.

With these ferro-cement experiments behind us, we went to Arkansas to try to rebuild our old retreat. In Arkansas, not only were we working on a tight budget, but had the added problems of being 35 miles from town, with only a small car for transportation. We needed to repair the roof on the old rock house, and on one section the old tin was completely gone and the rafters rotted away. We had no reasonable way to get lumber to our property, so we used native timber for the roof rafters in this section, but still needed a covering for the roof. I thought of the ferro-cement walls we had done in Florida and decided that, after all, a roof was just a wall laid flat. Because we don't normally walk on our walls, the roof would have to have more layers of wire. We used 2 layers of 1 inch chicken wire for walls and we used 5 layers for the roof.

I stapled tar paper right on to the roof rafters and laid down several layers of chicken wire. That is, I did this for as far as I could reach from the side of the roof. I gathered "road sand" from along side of the dirt road into our land and mixed it, a little rich, with Portland cement. I then forced the cement into the wire and waited until it had set up. I could then stand on that section to put the next layer of tar paper, chicken wire and cement down. I did this until the whole roof was completed. With 5 layers of wire and cement, we had a strong roof, but the process was pretty slow going. Once the roof was finished, we painted it with a concrete water proofing and it had no leaks. To get the most strength from the wire, I had to twist the ends together, on each new section, as I went and this was time consuming. Also the ends of the wire would sometimes stick my fingers, if I did not bend them down enough.

When we had to go back to Florida, to try to sell our sailboat and the land there, we found a section of old roof on the house, over the kitchen, that was starting to leak. This section was had almost no pitch and the water would sometimes stand there after a heavy rain. The whole section could be removed and rebuilt, or a new roof, with more pitch, could be built on top of the flat section. Both options were costly and time consuming. Why not ferro-cement? I laid down the wire and I hauled the cement mixture up in buckets, using a rope. With being able to do the whole section with the wire and being able to walk around, the job went much faster and the new roof is strong and water proof. I was even able to give the roof a little more pitch, so that water doesn't stand after a rain.

Recently a neighbor, who is a master carpenter and had been watching us doing our ferro-cement work, decided that he needed to build a 24' by 16' building, but lacked the money for siding, along one side and both ends. He came to me with a lot of questions about ferro-cement. "How long will it last?" He knew of one ferro-cement roof that is over 40 years old. "How does the cost compare with tin or plywood and asphalt roofing or siding for walls?" "How long would it take the two of us to do the cement work on his planned building?". We made a barter, I got to use his rototiller if I would help with the cement work on his building. (We don't like to rototill our garden, preferring raised beds, but some "care takers" (who did not "Care" but sure did "Take") had rototilled our raised beds into the ground, so that at least for this year we would have to rototill.

In one day we did all but one end of his building (he kept that end open so that he could put in plumbing for a shower and toilet). The walls of this building are treated 4"x4" landscape timbers, set every 4 feet, with "furring strips" (1"x2" strips) nailed to the timbers and the tar paper and wire fastened to these strips. As he could afford only one layer of 1 inch chicken wire for his walls, I was a bit unsure of how strong the walls would be. The finished walls surprised me with their strength. Maybe the old timers knew something when they only used one layer of wire?

Okay...Maybe you are now ready to consider using ferro-cement? "What does it cost?" 150x3 feet of one inch chicken wire cost me $27.00. Portland cement costs me $5.60 for a 94 lb. bag and here the sand is free, so I don't know what sand would cost. I have been quoted that a cubic yard (3'x3') of sand would cost about $30.00 and this would pretty well fill a pick-up bed. Tar paper runs about $8.00 a roll. You can buy the premixed cement, but be sure not to get the "Concrete mix" with rocks in it or the "Mortar mix". The price works out a little better if you get the Portland cement and the sand, and mix your own, plus you will know exactly what the mixture is. On that 24'x16' building, we mixed the cement a little rich. The normal mixture is 4 parts of sand to one part Portland cement. I usually mix 3 to one for ferro-cement.

Let's do some figuring. Say that you are doing a wall 25 feet long and 8 foot tall and that you want two layers of wire. The 150x3 foot roll of wire will cover the wall with just a bit of over-lap where the sections of wire meet. You would need about 4 bags of Portland cement and the right amount of sand to cover the wall. The cost for doing the wall with ferro-cement would be $22.60 for Portland cement, $27.00 for the wire, $8.00 for tar paper and about $15.00 for sand. (I am not even going to try to figure out the cost for staples and roofing nails to hook the tar paper and wire to the wall.) The costs come out to $72.60 You would need 7 sheets of "T-1-11" siding, or plywood, to cover the same wall. Even if you used the cheapest (1/4 inch), plywood, the cost is around $ 10.00 per sheet and this would still need to be covered with something to protect it from the rain. "T-1-11", which is much better siding, costs $20.00 or more per sheet. You could go with only one layer of the wire if you had to. The savings on the roof is not quite as good, because you need to use at least 3 to 5 layers of wire, but then you have a really strong roof that should outlast the plywood and asphalt type.

In doing this type of cement work, you will want to experiment with how much water you add to the cement. If your mixture is too thick, it will be hard to get it to completely fill all the spaces in the wire; and if it is too thin, it won't stay on the walls well. For roof work, you can mix it thinner. If your first coat is not perfect (they seldom are), you can later come back once the first coat has set up, and put on a finish coat. The best tool for this work is a "stucco" trowel and there are some that have a corrugated edge for making lines in the cement. What is the difference in ferro-cement and stucco? The ferro-cement is stronger. By starting at the bottom of the wall and working upwards, the cement will stick to the wall. In hot weather, mix the cement a bit thinner and you may want to spray the wall down with water before you start the cement work. You will also want to spray the wall down before doing a finish coat when the first coat has set up. This makes the second coat stick to the first better. Otherwise the dry first coat will suck the water out of your finish coat.

You can put designes in your wall, or leave it natural. For paint, we prefer the soft browns that give the house an adobe look. This could be used to build above or below ground pools, water tanks, the walls of root cellars, etc. When in doubt about strength, put on another layer of wire. When laying one layer of wire over another, make sure that the second layer overlaps the holes in the first layer (cuts the first hole in half). Using heavier wire like "Hog fencing" won't help, because it is not the size of the wire, but the number of strands that count. The tools that you would need to do this type of work are a wheel barrel to mix the cement in, a shovel for measuring the sand and Portland cement, and a hoe for mixing and a stucco trowel. You will want the cement to end up on the wall and not on the ground, so put a good amount on the middle of the trowel and place the bottom edge of the trowel against the wall and work upwards. Most of the cement that falls down will come around the ends of the trowel, so don't try to put too much on the trowel at one time. Press firmly as you move the trowel upwards to force the cement into the wire. It should stick to the wall. If you have a few places where the wire is still showing, you can come back a little later and cover these, or do them on the finish coat. If you can do a really neat job the first time, there won't have to be a finish coat, but it is often faster to plan on a second coat.

The dust from the Portland cement is bad news if you breath a lot of it into your lungs, so try not to stir up too much of this dust. Once it is mixed and wet down, there is no hazzard. It is difficult to do much cement work without getting some on your hands. Unless you have really sensitive skin, this will not cause any problems. Until I got a stucco trowel, I was putting the cement on with my hands. After you are done and have washed up, you might want to rub some hand lotion on your hands. You will want to wash all of your tools when you are done to get the cement off them. Pour the water from washing the wheel barrel some place where you don't want grass to grow. It helps to have a bucket of water handy and put your trowel in it when you are not using it. You can also wash your hands in it from time to time.

If you have cement work that you want moss to grow on, try mixing some potting soil and fertilizer in with the cement before you put on your finish coat. The potting soil, fertilizer, should take the place of one shovel of sand in the moss-growing cement mixture. This of course will not have the strength of regular cement, so it should only be used for finish coats. If something suddenly comes up and you simply have to drop everything, add more water to the cement mixture, so that it doesn't start to set up on you. Cement work that has set up for even a few hours will not be hurt by a light rain, but you need to try to plan your work around the weather. Don't test the strength of your work the day after you did it. Give it at least two days curing time, before you push on it or walk on it. Once the ferro-cement has set up, pounding nails into it won't usually crack it, but pounding nails into or around fresh cement may make it fall off the wall.

Ferro-cement walls and roofs are fire resistant, and once sealed or painted, weather proof. In very hot weather, small cracks may occur as the wall dries. This usually means that the cement mixture did not have enough water in it when it was applied. If this happens, wet the area down well and apply another coat of well watered cement. The second coat should be thin enough to enter and seal all of the small cracks. If, after you have finished the first coat and allowed it to cure, you still don't think that it is strong enough, you can put on another layer or two of wire on and another coat of cement. You may have a bit of a time nailing the second wire to the wall, but it can be done. For roofs, the cement mixture can be mixed up with more water and this will make it easier to get it to fill in around all the wire and make getting a smooth finish easier.

We think that "for the money", especially when you consider how long they should last with little or no up keep, the ferro-cement walls and roofs make good sense. Before putting the ferro-cement roof on our kitchen, I was up there every few months putting sealer on leaks. The thickness of a 2 layer wall is only about one inch and the roof with it's 5 layers is only about 2.5 inches. Ferro-cement can, if thick enough, support it's own weight. Our old kitchen roof tended to sag in places when I walked on it, and now with the ferro-cement it no longer does this. The only "down side" that we can think of with ferro-cement is that such a wall or roof would be very difficult to take down if you ever changed your mind. For an experiment, I plan on building a ferro-cement roof and then taking the roof rafters out, leaving the ferro-cement roof supporting itself. That should show people just how strong this stuff really is! If you have questions feel free to contact me.

Ken Davison
dragon@phonl.com

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