Ferrocement drip irrigation

Most people make ferrocement to hold water. I want to do the opposite: I want to make it thin so it drips water for irrigation.

I recently made a ferrocement bath for my pigeons. I was quick and sloppy, and when I finished it dripped dry in 24 hours. I put another smooth coat of cement on and took care of that problem.

But it gave me an idea: how about a long level trench, say 10 inches wide, 4 inches deep, coated in thin ferrocement, fill it with water every few days, and call it a drip line! It would be way cheaper, and besides, I can't even get drip line in the country where I live.

But, cement is, you know, fairly permanent. So I want to make sure I think it through real well first. Any thoughts?

I suspect that it will eventually get plugged up with algae, dirt, minerals, etc.

However, I'm a big fan of Empirical data, so perhaps you could build a small scale trial/experiment and see what actually happens.

Sounds like a big version of an olla. Keep us posted!

Why ferro? Why steel, rebar or mesh or anything includes iron? It is not going to carry any loads. As I understand, you want porous (or pervious) concrete.  As iron oxidize and since rust has more volume than iron itself, it will fail. By fail, I mean it will not serve the purpose intended. And since concrete lets water through, it will not protect iron. Why not pour concrete in sections with no reinforcement (max 1.5-2m lengths, though I would recommend max 1m to rule out settlement issues). You can build them as they do sidewalks, first odd  numbered sections, wait as much as you can afford (like 1-2 weeks or more - to rule out shrinkage of concrete) then pour even numbered sections.
Two problems might arise in the future: roots follow water and they will devour concrete. The other problem might be evaporation. Olla's work since they have a small opening, and water inside is not under direct sun light. Channel, on the other hand, will be under direct sun and most of the water might evaporate before passing through concrete.
If you don't have drip pipes, any flexible pipe, even the lowest quality or cheapest will do. Just put the pipe, seal one end and stab it with a needle (or pushpin) wherever water is needed. Those small needle holes might get clogged in the future but another stabbing tour the following year will do. Cover it with sand or soil or anything to protect plastic from direct sunlight. It will do the trick for the next 4-5 years and I believe it will be a lot less labor intensive (and possibly cheaper) than pouring cubic meters of concrete. I really liked your idea and it is interesting. The main problem is that you can easily lay down more than 300 meters of pipe in less than 30 minutes.

You can make a trench by having some hession or cloth cut to size and dipped in a slurry of cement and water, with some fine sand.
Make the mix like cream.
Dunk the cloth in the mixture and lay shaped into you small trech and let it dry.
You could make a mould from ,say a 4 inch pipe or log, and lay your soaked cloth over that.
When it dries lift off and place in another trench.

s. ayalp wrote:Why ferro? Why steel, rebar or mesh or anything includes iron?

My thought was that if I don't have reinforcement it would crack up--seeing as my point is to make it pretty thin. Say if somebody stepped on it...

John C Daley wrote:You can make a trench by having some hession or cloth cut to size and dipped in a slurry of cement and water, with some fine sand.

That is a fascinating idea. And suddenly I'm thinking of all kinds of applications for that technique too.

Nathanael Szobody wrote:

s. ayalp wrote:Why ferro? Why steel, rebar or mesh or anything includes iron?

My thought was that if I don't have reinforcement it would crack up--seeing as my point is to make it pretty thin. Say if somebody stepped on it...

John C Daley wrote:You can make a trench by having some hession or cloth cut to size and dipped in a slurry of cement and water, with some fine sand.

That is a fascinating idea. And suddenly I'm thinking of all kinds of applications for that technique too.

They make fiberglass re-enforcement, should last a while without deteriorating.

Neat ideas!
I have idly considered irrigation  ponds for individual trees, or  irrigation  canals running through a food forest.
By selectively finishing the inner surface of thr pond or canal,  the plants can have access to water a little at a time.
This could also be a way to make large ollas.
A huge olla could be kind of like an infiltration basin,storing water that would otherwise leave the land.
A purposely porous pipe could store and move water.
A big olla at the lowest spot in a yard,could be a shallow well.

I think you could do it with terracotta pipes? Like ollas, just pipes instead...

I envision putting the ollas IN the canal, the opening of them flush with the bottom of the canal. Wherever there is an olla, a tree is planted. The rest of the length of canal is planted with smaller species. Preferably fast-growing ones to shade the canal and minimize evaporation. In my climate moringa, chaya and pigeon peas should do the trick. Add some cucurbits for good measure.

Now my son just got an aquatic turtle and wants me to build a pond for it. I'm inclined to acquiesce. So at one end of the canal is a leaky turtle pond feeding two papaya trees. Irrigating everything consists in throwing the hose into the turtle pond every few days until it overflows with nutrient to the food forest through the canal, filling all the ollas on its way. Eh?

Dawn Hoff wrote:I think you could do it with terracotta pipes? Like ollas, just pipes instead...

They make them too well; they won't leak properly. I can't get those here anyway.

Nathanael Szobody wrote:
My thought was that if I don't have reinforcement it would crack up--seeing as my point is to make it pretty thin. Say if somebody stepped on it...

Nathaneal I believe there are limits for minimum required thickness and they are mainly aimed to protect reinforcement from corrosion. So that there will be no water penetration. General rule of thump: for surfaces in contact with wet soil it is 10 cm (4 inch), dry soil 7cm, with air 5 cm and such. It is exactly the opposite of what you want to achieve.

What I am proposing is not regular concrete. Mostly gravel and cement and a small amount of sand. If you can choose sand and gravel sizes and proportions perfectly (aggregate) so that they will fill each voids perfectly and you will have perfect nonporous (water tight) concrete. This was how they made concrete for water tanks and similar 50-60 years ago. Nowadays, though ratios are still very important, we have additives, guaranteeing success. We want to achieve the exact opposite, limit sand ratio so that voids between gravels are not filled. Water will use those voids to pass through. So what I would do:
Increase cement ratio to hold gravels together. You would like to have a smooth surface, no big rocks sticking out, so limit max grave size to 20-25 mm's (reference). Include latex or such to protect it from frost (I believe you don't need that in Chad). Roughly 1 unit volume of cement + 3 unit volume of gravel + 0.5 unit volume of sand to increase strength (or no sand!!) (using fine sand will increase strength but limit porosity) will do the trick. Adjust the ratios for the aggregate sizes you have. Increase amount of sand to slow down drainage, decrease amount of cement to cut cost. Hold the gravel volume same for each trial, play with sand-cement ratios so that you can see the difference. I think couple of trials will perfect ratios. You would like to increase sand ratio, so that the whole channel gets filled with water first.

About thickness, it will define how much water can pass through in a certain time period. So, for 10 cm thick pervious concrete, say, 2 liters of water can pass in one hour, for 20 cm thickness only 1 liter of water will pass in one hour. I would not select less than 20 cm thickness for pervious concrete. 15 cm might do, depending on the quality but it will crack. Since it is thin, I would keep each section length to 50 cm. If you pour concrete in one go, when it cracks, it will crack wherever is the weak. Concrete will crumble. If you pour concrete in sections, a nice straight crack will form between sections. It is not going to a pose problems for your purpose.

Hope it helps.
Here are some youtube videos:

youtube video
another video

Ayalp,

Thanks that's very helpful. I will watch that video in a few months when I have a better Internet connection in the capital.  

I now recall seeing an entire defensive wall poured out of pervious concrete on a 19th century fort. The gravel was huge. Apparently it was to prevent cracking in winter because it was so pervious it didn't retain water at all. It also made it more absorbant of canon fire apparently.

Now that I know HOW concrete is made pervious, I'll see what I can come up with. Thanks!

Try the hession system first.
Its low cost, it works and does not have the issue of fibre glass which by the way I imagine you don't have readily available anyway.
Send us some photos when you can.

John C Daley wrote:Try the hession system first.
Its low cost, it works and does not have the issue of fibre glass which by the way I imagine you don't have readily available anyway.
Send us some photos when you can.

I really like the idea of this technique for a lot of reasons and applications. Particularly it makes me think of an easy way to make planters to hang on a wall for a "living wall" type garden. However, for an irrigation canal I'm skeptical that it would hold up. Imagine it getting stepped on. ..

If people are going to be walking on irrigation channels, then you have a problem.
Based on your initial issue of not having drip lines available, the use of traditional concrete structures may be over kill.

Further traditionally, earthen channels alone were used for centuries.
I have worked in the Australian irrigation industry and earthen channels are still used today.

John C Daley wrote:If people are going to be walking on irrigation channels, then you have a problem.

Agreed. But stuff inevitably gets stepped on.