Ferrocement Water Tanks?

Hi Jan,

With any cement tank, you have to make sure that you are not in a bush fire prone area. Poly tanks are actually better at surviving a bush fire than concrete based tanks. The reason for this is that poly tanks will melt down to the water line where thermal mass stops the tank melting further than that.

Concrete based tanks on the other hand tend to collapse, because water always infiltrates the concrete and during a bush fire, the water gets hot, turns to steam and cracks the tank with often disastorous consequences.

There is nothing inherently wrong with burying a poly tank in the ground unless the ground has subsided around the tank. You probably should not drive a vehicle anywhere near that tank as it will be compacting the soil and may deform the tank.

I'd probably dig it up and place it above ground. Hopefully the poly tank - and we use food grade UV treated polyethlene here - has been treated for UV protection which is a serious issue with outside plastics in Australia.

Regards

Chris

I, too, have built a ferrocement boat many years ago.  It would seem to be a fairly easy task, especially since a tank wouldn't normally be of compound curves or need to look good in a coat of shinny paint.

I built a boat of Lloyd's specs and was 35 feet long and 1/2 inch thick.  It was built of 3/16th mild steel rods (easy to bend) and two layers each side of 16-guage square welded high-tensile mesh.  This is much stronger and thinner than the chicken wire version.  Easier to get cement through, too.

I would probably build a bottom first, maybe with some rebar to strengthen the bottom.  Then lay up the outside bottom with enough overlap to go up the sides.  You could then lay this in a hole and finish the rest.  This is very old technology, well tested.  The drier the cement the less porous and the stronger, especially with 30-day water curing.  Then leach the lime out of the microscopic tunnels left by the water escaping and seal.  Typical sidewalk cement rates around 2000psi.  The boat I built had concrete that measured, at the end of the 30-day cure, 20,000 psi.  A direct attack with a sledge hammer had no effect more than a surface blemish.

Hi Jan,

Ferrocement tanks have several advantages over tanks made of cocrete or brick like they are
usually cheaper to build and require less skilled labour, they are able to withstand shock better, as ferrocement is more flexible, small ferrocement tanks are portable.

Hi Jan,

You should check this guy out.  www.annesley.wordpress.com

He is doing some amazing stuff with alternative building including domed roofs with built in catchment and ferrocement cisterns.  He broke the cost down to about 30 cents a gallon for his cisterns and he goes into some good detail.  He built multiple tanks rather than one big one for a couple of reasons; the smaller (1,000 gallon) tanks do not need to be as strong and he has multiple tanks in case he needs to repair or clean one and thus preserves the bulk of his water supply. Opting for resilience over efficency. He writes a bit on the idea of constructing a cistern our of earthbags and a 20 year "pond liner." 

I have one other thought.  I need a tank yesterday but limited mortality, time, and finances have me looking at a "temporary" solution.  You can buy a replacement swimming pool liner really really cheap if you shop online. (Under $100.) I assume they come with ports for filters and such and there are some that are designed to just hang over the edge of the frame.

I have seen "temporary" tanks that were liners in a (very very sturdy) wire frame.  I am seriously considering getting one of these with the added benefit that the "frame" I build becomes part of the structure of a future ferrocement tank.  (I do so hate to waste.)

There are many sites about ferocement boats.  If it can hold the water out in rough seas, it will be able to hold the water in a tank.  Using layers chicken wire tied into a frame of light rebar and then mortar forced into th mesh is pretty simple.  A vibrator of some sort helps to get rid of air pockets.  The mix is rather dry compared to mortar for bricks as the steel does not soak up the moisture like bricks do. It does take a bit longer to get good strength and for a few days, you must mist a water spray on it. 

I helped with a 55 foot FC boat about 25 years ago.  Last heard, it was still afloat. Hope this helps.

Lindy

About twenty years ago, I built three ferrocement rainwater cisterns, with the largest being about 15 feet in diameter and 5 feet tall.

I did all the labor myself, and it was pretty exhausting. I used 1/2" rebar (#4) that I bent by hand, and then covered the inside and outside of the rebar with galvanized steel lath (the type you use for plastering). I pushed mortar mix into the mesh from both sides.

After applying an interior coating of a cementitious waterproofing compound, the cisterns held rainwater for many years without any leaks.

 It seems like a good technology to carry into the future we'll be living in - requiring only cheap, easily available materials combined with a lot of manual labor. 

Hi Jan,

Reinforced concrete water tanks are very common in rural Australia and have been in use for many decades. Lately, though, poly tanks have been taking over, as they are cheaper and easier to handle. They seem to have a pretty good life span too, but I don't know how they compare to concrete. Certainly cement is an easy repair, although poly tanks can also be plastic welded.

There are many commercial suppliers of concrete water tanks in Australia, but I believe they construct them much like a concrete swimming pool - that is, steel reinforcing mesh formed into a central skeleton, then wooden form work built on either side. The concrete is then poured in to fill the gaps.

I reckon a post to the appropriate forum at http://aussieslivingsimply.com.au/ would get you replies from people with hands on experience.

As an interim, have you considered digging up your existing tank and using it above ground?

Best of luck,

Homesteady