A shed is a thought, but it would have to be at least a couple of feet taller than the tank in order to have access to the manhole on the top.

I would be doing rainwater collection off a metal roof. Filtering the runoff would keep most debris out of it. Without sunlight, there shouldn't be any algae growing in the water, and the kind that grows on the side/bottom of the tank is not a worry to me.

This would mostly be for watering the garden, and for drinking water if backup should be needed.

But 4" of concrete isn't really needed unless you're working with that watery slop that the trucks deliver. The more water added to concrete, the weaker it is.

I've been working with concrete for about six years now, and I know that when the concrete is made with minimal water, it's very strong. Most of my pieces are only 1/2-5/8" thick, and hollow. However, I am not sure about the expansion/contraction issues with the tank vs. the concrete shell.

There has been quite a lot of work done in Africa and the Middle East using Watt's ferrocement methods, and quite a bit of construction with thinwall ferrocement for roofs in temperate climates (including Alaska). The thinwall tanks do stand up to the weight of the water, but freezing temps are not an issue there, which they are here. I am suspecting that the bulk of the water (another reason for such a large tank) might offset any freezing issues for the temps we get here, but I don't really know.

Sue

Sue how hard would it be just to build it out of concrete? My friends (both in Tenn and Portugal) have concrete above ground cistern that is all concrete made simple and no plastics and have been used for water for over 30 years (Tenn one). If I ever decided to build one I would probably go that route because:
1. I hate plastics period (chemical leaching,out gassing (learned that about food grade plastics from Nasa) etc..)
2: Simple to build
3. Highly reliable (from what I've seen)
4. Extremely Durable
5. Most (over 99%) of the places I visited in Portugal (on the island) are depending on concrete cistern as their only primary of water with all new houses are built with them and they have lasted for more years than I know of.

I always like to go with a reliable system that I can build it and spend as little maintenance and have the best reliability and durability and I don't care for plastics (did I mention I hate plastics,hate the taste as well)

Here's one outside of the place we stayed at (wife's parents) and she was born in this house and it's been there for a long time (she would kill me if I say how old it is because it may reveal her age )(hint it's wy older than the Tenn one) but needless to say it would last a lifetime with little maintenance and all concrete.

Sue, How rocky is your soil? Could you use a track hoe to dig the hole, yes i know that you are trying to do this as inexpensively as possible but you can rent a TLB or a excavator for $300-500 for a weekend. And you can not only dig the hole you can use it to put the tank in place. Of course if the rocks are the size of cars this still is not a good idea. If you decide to do this be sure to call your local underground locating service before you dig.

If you cover the tank with concrete can you put styrofoam or some other insulating material between the tank and the concrete. Don't know if the concrete has enough insulating value to keep your tank from freezing where you are at. I have seen structures made with made with styrofoam blocks and concrete on the outside. The concrete adheres well enough to the styrofoam to be shipped, stacked, and the blocks joined together on site.

For your thin concrete work are you using fiber admixtures to increase the strength? Or are you using just portland and sand with just enough water to achieve hydration?

Susan,

A home made ferro-cement tank is a lot of physical work and takes plenty of planning, but is possible.

Ferro-cement vessels are not new. During WWII some liberty ships were made of ferro-cement. As you probably know, cement theoretically never finishes drying. This factor was made clear when those liberty ships kept settling lower and lower in the water. The last I heard, which was along time ago, those ships were still being used as a breakwater somewhere along the southwest coast. The problem was the cement used in those ships had a soluble chemical that was released as the cement dried. Over time that chemical was displaced with water. Making the ship heavier.

Back to the subject. Ferro-cement is a combination of ferric metal, usually rebar, and cement. The strength of a ferro-cement structure is the metal and the glue and filler is the cement. Before there was precast structures, I designed structures used underground in all the various soil types. As you stated, for standard cement, to much water weakens the mixture. But with less water, it is harder to work. The actual design to strength of the structures I specified were fairly thin, but it was physically very difficult to make the thick cement mixture flow to the bottom of the form around and through all that rebar. If we over used vibration techniques to get the cement mixture to flow to the bottom of the form, we would have the heavier aggregate settle below the fines which weaken the structure. Inadequate flow resulted in voids. To combat this problem, I changed the design to make the forms wider. This increased cost and weight but it worked.

You might try the ferro-cement boat building technique of forming the tank with rebar. The bottom, sides, and top all at once. Don’t forget the input and output fixtures as well as the access lid and provision for a ladder. There are many books on ferro-cement boat building techniques. Now for the really hard part. Get a number burley men and on both the inside and outside of the tank have them force the thick fairly dry cement mixture into the rebar tank structure between them, similar to a riveter and his helper. It is best if this task can be completed in one day for the bottom and sides. The top can be cemented later. Just don’t be the one on bottom of the top pushing up. It is very tiring and messy. Remember, neatness counts. There are chemical adhesives that let you continue between successive days if you can’t finish in one day but it is second choice. You won’t have a problem with different expansion rates between rebar and cement with such a small structure. Remember for every foot height of water in the tank the pressure per square inch increases by 2.31 pounds. So, a seven foot high water tank will have a force of 16.17 pounds per square inch at the bottom of the side walls.

There are a number of coatings you can use to line the tank. Some have been used for thousands of years. Ceramic tile is one of them. Don’t think that bacteria, mold, and algae will not grow without sun light. Every pore in the cement will harbor nasties and will be difficult to clean. All concrete pipes now used for water distribution are ceramic coated on the inside to avoid this problem.

Also familiar yourself with confined space safety procedures. I have a good video on the subject but it is for commercial applications. The best procedures can be condensed into three steps. Purge, test, and ventilate. Rent a ducted ventilator and an explosive gas detector. Once you determine the cubic volume, there are tables that tell how long you should vent the tank. Then test for explosive gases. Once your inside the tank, keep the ventilator on full time. You don’t want to fall victim to inert gas narcosis. Don’t throw in a lit match to test instead of using an explosive gas detector. I saw an idiot do that in down town Salem, Oregon during rush hour one morning and watched as successive manhole covers blew off for blocks in four directions.

If I can help further, if you call this help, let me know.

A local landowner wanted to have a pond. He rented a backhoe and dug a hole roughly 75' in diameter and about 25' in the center. He ran into a bit of rock outcropping that was too large to shift so he moved the pond over about ten feet from his original location. Once dug he had a construction supplier dump in a few cubic yards of builders sand. This was spread and roughly compacted. Then he rolled in a thick black plastic membrane. Took about a day and a half.

He runs a pump to aerate the water and limit algae growth. His kids and black lab swim in the water and it stays mostly full just from rain. If it gets too low he tops it up with well water.

It has been there for about fifteen years and it is still kicking.

I priced out the tanks as we want to get one too.

2500g is the tipping point where price goes up significantly. I believe 2 x 2500g tanks are cheaper than 1 5000g tank.

Can you not just put it under some trees?

I think a shed would be cheaper and easier than concrete, and you can make it a bit larger to store other goodies inside too : )

Please, if you do this post pics and info I would love to do a 2500g tank this summer.

To tell the truth, I really prefer the ferro-cement tank idea. Like Falcon, I am not fond of plastic, and I know the concrete tanks have worked very well for many years in many, many parts of the world. Even here!

After I posted, it occurred to me that I could make a couple of smaller tanks instead one one huge one.

Ray, I've seen earthmovers work in the soil here, and the sheer number of rocks drives me crazy! It's taken me several years to get the surface rocks collected so I can mow the back field (2/3 acre), and I am sick to death of picking up rocks. That's why I want to put it on the surface, to hold the darned rocks down! ;-)

I have fiber for the concrete, but I haven't used it yet for anything.

Turbo, that all sounds like good advice. After reading your post is when it occurred to me to make smaller tanks. I recognize the problem with getting the concrete completely worked into the wire (etc). I've worked with a single layer of chicken wire, but not multiple layers, heavier mesh, or rebar. And I hadn't thought of lining the tank... a new idea.

And thank you for the info on the gas problems. No matches, eh? Right! I'll use my lighter! *grin*

Art, the problem with ponds is the liability, permit and insurance issues. I really would like to have a pond, but... Of course, if I could remove all the rocks, the top of the soil would probably drop at least a couple of feet.

Thanks for all this info. I'll have to ruminate on it.

Sue

Same thing here: once you get rid of the rocks, you have to go buy dirt to fill the hole in...or put an outhouse on top of it.

There was an earlier thread about Cisterns on here that deserves a look at.
It had comments about underground and about above ground water storage tanks.

http://forums.equipped.org/ubbthreads.ph...true#Post162331

Western Washington is full of Glacial till, full of Basalt and Granite. As one who spent a good amount of my childhood working in the "Rock Pile", which is what we called our yard, I can say firsthand digging in that soil is costly. When our neighbor put a pool in his backyard, we were offered $45 for every tiger tooth we could find that was broken off the bucket of the excavator they were using. When they dug out the foundation for our home, they left a row of granite boulders along one property line, which we covered with fill soil and planted shrubs in.