How to make ferrocement garden beds

No-dig garden beds with ferrocement edges all finished

Ferrocement (sometimes called thin-shell cement) is a construction technique where cement is thinly applied to a sturdy steel or wire frame. It is very cheap and relatively quick to do, and produces extremely strong structures.

While it does involve cement, which has quite a large energy footprint, the resulting strength-for-inputs equation means it is a suitable and ethical option for some structures, particularly those requiring great strength.

We’ve been wanting to have a play with ferrocement for years, but weren’t quite sure how to go about it, or what to build. Recently our friend Tom arrived at Milkwood armed with the right knowledge however, and suggested we update the kitchen garden at basecamp by incorporating some new no-dig beds with ferrocement edges.

Ferrocement watertank construction in progress. Photo by Darren Doherty

As always, when trying out a new technique, it’s best to start small. So we held off on making a ferrocement boat, watertank, house or grain silo, all of which ferrocement is (apparently) commonly used for around the globe.  We thought we’d just start with a garden bed or two, and take it from there.

The possibilities of ferrocement are endless – if you can make a frame to the shape, cover it in chickenwire and pat a thin veneer of cement onto it, you can make it out of ferrocement.

For our basecamp kitchen garden, we decided to keep the existing contour beds (which needed a bit of love after winter anyway), take them apart and enclose them with ferrocement edges about 30cm high. This means the edges of the beds will be better defined, the ferrocement edge gives us something to lean on when we pick from the beds, and the beds will be able to retain a certain amount of water at the bottom of the root zone in dry periods, rather than that water wicking into the drier paths.

The ferrocement edges also mean we can build up the deep mulch in these no-dig beds higher than if they were just heaped up from path level, which will help with evaporation here in our high and dry summer climate.

Completed ferrocement garden beds with herbs, mulch and lots of summer seedlings

So. Here’s what we used to make our ferrocement garden beds: we were able to make these out of mostly recycled materials and they turned out beautifully.

Materials

  1. Various lengths of recycled “rebar” – the reinforcing bar usually put in a concrete slab – any scrapyard would have some.
  2. Scraps of recycled chicken wire
  3. “Rebar ties” to wire the chicken wire to the Reo Bar (because we already had them) – but you could just use bits of wire
  4. Sand mixed 3:1 with cement (three parts sand to one part cement)
  5. Wheelbarrow for mixing cement and something to mix it with
  6. Water
  7. Gloves

Defining the edge of the beds

First of all, we clearly defined the beds, dug out the paths and created a small channel around the outside of the beds where the ferrocement would go.

Propping up the rebar against the beds to check for length

The next step was to define how much rebar we needed. We laid it out around the beds.

Andrew cuts the rebar to size and removes the bottom cross-bars

Then we cut the rebar to size, and took the crossbars off the bottom squares. This meant the vertical bars of the bottom squares could act as spikes to hammer into the ground, keeping the rebar edge vertical.

Whacking the pre-bent rebar into the ground to stabilise the structure

Next we bent the rebar to the shape of the bed, and hammered it into the ground.

Andrew and Tom attaching the chicken wire to the rebar structure

Next we covered the rebar in our scraps of chickenwire and attached them with the rebar ties.

Andrew and Tom. Who needs a cement mixer when you've got a wheelbarrow!

Time to mix the cement. Apparently the recipe is 3 parts sand to 1 part cement, and then add water slowly, stirring all the while, until you have something the consistency of ice-cream, or until a line drawn with a finger lightly through the mix only just falls back in on itself.

Tom pat-pat-pats the cement onto the structure... a bit slow going, this part!

The application of the cement to the wire took a while. Lots of pat-pat-patting. You get the hang of it after a while. We did a first rough pass followed by a smoothing second pass.

Alexe applies oxide with a paintbrush to make the garden edges look lovely

Once the cement was semi-dry, we brushed on some oxide (cement coloring) mixed in water. The cement drinks in the oxide and this way you get an aesthetic finish which doesn’t involve any paints.

Ferrocement garden beds in progress, with permablitzing PDC students to right. Note all the tomato stakes sticking out of the newly made ferrocement walls

One thing to note is that we wanted to ensure that water could exit near the bottom of the ferrocement walls, to prevent waterlogging of the beds in a heavy downpour. To do this we stuck a bunch of tomato stakes through the rebar before applying the cement, and pulled them out once the cement was all in place. This created a series of holes low down in the down-slope wall of each bed.

Ashar and Adam hanging out in our new kid-friendly kitchen garden

Ashar and Adam (Milkwood intern) hanging out in our new kid-friendly kitchen garden

And once they were done, we mulched heavily and now we’ve been busy planting our spring seedlings, packing our new-fangled beds through of good things to grow and eat over summer.

In retrospect, this technique has both pros and cons. The good things about it include the cheapness and accessibility of materials (which is probably why it’s used in hard-to-get-to locations around the globe), and the not so good things include that its relatively labour intensive. So, like any construction technique, it’s perfect for some scenarios, and not so much for others.

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Would we use it again? Well, we’ve been trying very hard to figure out how to do a large wicking bed system for our Milkwood kitchen garden. We definitely want to use wicking beds, but we definitely want to avoid plastic, so we need some other sort of water-holding reservoir for the bottom part of the wicking beds, which is also very strong. Ferrocement might just be the answer – we’ll keep you posted as we finalise that design…

Ferrocement resources:

Big thanks to Tom Bell for his energy, enthusiasim and knowledge. Big thanks also to our fabulous interns Andrew, Adam, David and Alexe who got into it and made it happen (especially Andrew for his photos). Our future vegetables and herbs, and all who will eat them, tip our hats in your general direction!

8 Comments

  1. Sam H
    Posted November 8, 2010 at 10:41 pm | Permalink | Reply

    I saw some ferro cement wicking beds in Hay. I’ll take a picture and send it to you.

    • Posted November 9, 2010 at 9:11 am | Permalink | Reply

      That would be awesome, Sam. Much appreciated – were they working well?

  2. Joe
    Posted December 1, 2010 at 11:33 am | Permalink | Reply

    Make a ferrocement reservoir no higher than 12 inches, 10″ might be better, can’t have it too high or it won’t wick up enough. This will be placed in the ground, the top of the reservoir will be at ground level, below your raised bed garden. Lay a black perforated 4 inch plastic pipe length ways( or make a concrete pipe if you don’t want to use the plastic )along the bottom of the reservoir and up to the top of the finished raised garden bed. This is how you fill the reservoir with water after all of the compost has been put into the bed and the reservoir has been covered up. When it rains water will over flow from the reservoir and out of the raised bed as long as there is a drainage hole provided for that purpose. The reservoir can be filled with screened compost, small wood chips, or pea gravel, anything that will allow water to wick up to the plant medium. After the wicking material has been put in the reservoir, fill the reservoir up with water and make sure the wick material is completely soaked and is firmly packed down. Next, fill the raised bed with plant medium (ie. compost). It is better to wet all of the plant medium before you put it into the bed. Make sure the plant medium is something that will allow water to wick up to it or the wicking process won’t work properly. I use 1/4″ screened compost that I make myself with cow manure.
    This should get you started.

  3. Anna Lee of LuLuLand
    Posted February 13, 2012 at 4:24 pm | Permalink | Reply

    I am loving this discussion of wicking beds using non-plastic materials and especially the concept of ferrocement projects. One thing for sure, if you use ferrocement structures you had better make sure you want them for keeps! They are amazingly strong and you won’t want to take them down!

    I used 1/4 inch hardware cloth wire mesh for some of my beds. I folded the cloth over to double it which achieved two things: the top edge was not sharp, and the mortar didn’t pass through to fall out the other side as easily. Makes the process a whole lot faster. The 1/4 inch size is more flexible and can easily be shaped whimsically, such as my kidney and heart shaped beds. A whole mandala of shapes and verticle structures could be made this way.

    These structures are simply sitting on the ground and could conceivably be lifted and moved as one to another location if need be. I’ve had no trouble with drainage this way and we do get some monsoon type rains here.

    We have beautiful red clay/sand mix here in the north Florida area. When the cement dried I mixed portland cement with my clay/sand soil and painted it onto the surface. That way I had a beautiful color and natural materials for achieving that. One could also use an outer layer of cobbing mix. If one has the desire, mosaic tile or glass pieces can decorate the outer walls.

    I have made many structures with cement and bottles and cement and soda/beer cans. Now I am thinking of how to use these materials for making wicking beds. I am working on several water containment structures, two of which are can and cement construction a la Michael Reynalds Earthship designs and one with various wire and cement.

    For these to contain a good deal of water one must be cautious about the strength and design shape of construction and the internal coats of cement for keeping the water from winnowing its way through and causing leaks/cracks and eventual failure.

    But for the wick beds you are not so concerned to the same extent bcause you are not dealing with the same volume of water, degree of pressure on the walls, and the necessity of retaining all the water. You allow for drainage/overflow and are mainly concerned that the majority of the water is retained by virtue of not only the integrity of the structure, but also by the materials in the bottom of the bed.

    Rocks and heavy mulch have been mentioned for the reservoir, and for some folks rocks are readily and cheaply available, but I try to limit the costs and use as much recycled materials as possible. Some folks are using aluminum cans which can themselves contain water and some good thinking might come up with the best way to configure the cans for this purpose. However, I don’t like aluminum coming into contact with my water and soil…maybe just a prejudice on my part.

    So I am thinking of glass. The ideal would be the cut off necks of bottles which would hold a certain amount of water themselves, and would not rot or rust, and cause no harm even with their cut edges as they are well underground and out of reach in this instance. They would not offer the type of surface that rocks would for engendering certain bacteria, which could be seen as either a plus or a minus. The bottoms of the bottles could be used for glass bottle brick wall construction, or cut an inch long or so and turned over to line the soil at the bottom of your wick bed with spaces filled in with mortar (or even clay) to create a fairly water-proof bottom liner.

    If you then used the ferrocement wall structure of your choice for the wall portion and set in a cement seam at the juncture of floor and wall, you would have a fairly water tight structure, I think, and one that would last a long time.

    As with the rocks, the glass bottle pieces would offset enough space compared to a purely water filled container to make the question of water pressure not a concern even if all of this were above ground..

    I realize that digging a hole for the reservoir portion of the wick bed makes sense in many ways, precluding the need for a wall aside from the earth until one gets to the garden bed portion. However, the idea of a much taller raised bed makes a lot more sense from the perspective of the ease on ones back in tending to the garden. So the entire structure could be made as described above with the reservoir starting at ground level and the side walls coming up two feet or better.

    The additional height would not be a problem for the wicking question if one had strips of cloth coming down into the reservoir and reaching the cloth that separates the reservoir from the bed which would then wick laterally along the cloth itself as one possibility. One could also deepen the reservoir portion and assume the water table would be kept within the reach of the soil section at any given height.

    The “tube” that delivers the water from the surface into the reservoir could even be made with glass bottles where the bottoms have been cut off and the remaining body joined to the next bottle and not sealed so that water leaks through the joint as it does through the holes in the pipe aforementioned. Of course, if one has the time, holes can be drilled into the bottles.

  4. Posted March 10, 2013 at 12:44 pm | Permalink | Reply

    Thanks heaps for the great idea! Can’t wait to get started on a ferrocement herb spiral!

    • Posted August 8, 2013 at 8:50 am | Permalink | Reply

      And it turned out GREAT:

      Thanks again for the recipe guys :-)

  5. Esbjorn Aneer
    Posted June 17, 2014 at 5:41 pm | Permalink | Reply

    Thanks for the article, great! I have been looking for info on this. Want to make a grey water treatment system from ferro-cement tanks.

    There seems to be an issue with the links in the ‘resource’ section… I can activate the first 4 only if I hold the mouse over the ‘F’ of the line/link. The last one I can’t seem to activate at all.

    You are doing such great work sharing the things you do! Thank you.

2 Trackbacks

  1. [...] (often used in rendering outside earthbag installations) – ferrocement garden beds in the Milkwood Farm kitchen garden, and an earthbag seat project using [...]

  2. […] solution came in the form of ferrocement!  Thanks to a post by Milkwood Permaculture my dilemma of stopping grass invasion whilst maintaining curviness was solved.  I’m not a […]

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