How to make concrete or mortar that can harden underwater, from scratch.

 

Have you ever wondered how people made concrete before there were bags of ready to mix cement? Well good news, you're about to learn.

 

Concrete is one of the strongest, and most versatile building materials that mankind (or womankind, I irritate them, but I don't discriminate against them) has at its disposal. It's instant rock. "Just add water". Kind of like the Wal-Mart brand corn tortilla mix, only it doesn't smell funny. The problem with concrete is the price. The high price tag stems mainly from the fact that industrial concrete plants require massive amounts of energy. This is no less true of homemade concrete however, due to the smaller scale, it's more manageable. That said, you really need one heck of a bonfire for this one.

 

The main ingredients of cement are quicklime (which is made from limestone), sand, and aggregate, which is normally gravel. To make "hydraulic cement" (cement that can set underwater), you'll need terra-cotta in place of sand.

 

Making Quicklime. Limestone, seashells, bone, and chalk are all made of calcium carbonate. Any of these materials can be used to make quicklime, although limestone is more readily available in large quantities. Limestone occurs all over the world.  You may well have limestone on your property and not even know it. After all, it makes up about 10% of the sedimentary rock this side of the Earth's crust. It is also available at most lawn and garden/home improvement stores relatively cheap for use in landscaping. But with limestone, remember that the whiter the stone the more pure it is. Purity is especially important if you plan on making hydraulic cement. If you only need a small quantity of hydraulic cement, I suggest using chalk for that reason.

To make quicklime, you’re going to need to build a really hot fire. You're going to have to get your material glowing white-hot for this to work.  This is easier in a kiln, but can be done with a bonfire. Take your limestone, seashells, or chalk and place them in the fire. Be sure to keep the fire burning hot around them, while also raking coals around them to get them as hot as you possibly can. If you're using powdered chalk or small pieces of limestone, you may want to place a steel plate in the fire to place your limestone on.  The calcium carbonate (CaCo3 ) will go through a chemical reaction in which carbon dioxide (CO2) will be cooked off, leaving calcium oxide (Ca0), a.k.a. quicklime. Once your quicklime has cooled, use a brush to remove any impurities it may have picked up in the fire. It's important to remember that although you can store quicklime in an airtight moisture-free container, quicklime is highly caustic (so use gloves when handling it) and unstable. (Relax, it's not gonna blow up. I'm not going to teach you how to make anything that blows up for three reasons. One: I'd rather teach you something useful. Two: my family made me promise not to.  In the words of my mother, "Please, don't put some poor parent through what I had to go through when you were growing up". Three: It’s just too easy. So, if you are one of the small contingent of people who know what I do for a living, and are waiting around for me to teach you how to make a bomb….You're a moron, grow up). By unstable, I mean is difficult store to for long periods of time without it slaking.

When water is added to quicklime, it becomes slaked lime. This creates an exothermic (that's fancy talk for it gets hot) chemical reaction in which the water is expelled leaving behind a solid rock. (The hissing and bubbling are not a part of the chemical reaction. That's actually black magic, so draw a cross on your forehead to keep the devil from climbing in through your butt and taking over your body.) This is where the magic happens. By adding aggregate and/or sand, you can create a concrete wall mortar to suit any application. Again, use gloves.  This stuff can take your skin off.

I'm going to give you recipes for several basic mixes; however it is important to remember that different mixes work better in some areas and climates than others. To find out which mix work best in your area, you can look it up on the Internet. (Unless you get extremely lucky, this won't work). You can do some small-scale experiments of your own. The best way I have found to do this is to ask an old-timer. I'm serious.  They have done all this stuff before. In most cultures, the elderly are held in a place of honor. One of the many downfalls of our culture is that we toss them away in "homes" and stop listening to them. They’re old.  They are not children, nor are they stupid…unless they were stupid before they were old. Anyone who is interested in homesteading, survival, self-sufficiency, gardening, building or hell, anything else for that matter, can obtain a wealth of all but forgotten knowledge for the price of a cup of coffee.  Oh wait, most places give seniors free coffee!  Knowledge is, without a doubt, the single greatest resource humankind has access to. To ignore those who have almost a century of that knowledge is completely, and utterly asinine. Young people, let's not forget that they were at one time farmers, construction workers, sailors, soldiers, housewives, welders, cooks and doctors. They were brilliant inventors, brainless jocks, dirty little schoolgirls, and they were that weird guy that everybody likes and nobody understands. They were the loved, the hated, the strong, the weak, the courageous, the cowards.  They were us.

Before we get into actual recipes, it's important that we first discussed the mason's paradox. It is thus, "The more water you add to the mix, the easier it is to work. The less water you add to the mix, the stronger the final product will be." You have to add enough water to get the entire mix at least damp. But beyond that, the choice of how much water to add is up to you.

Basic Cement Mix

1 part quicklime

3 parts sand

3 parts aggregate

Slake the quicklime the first, then add your sand and aggregate.

Basic Mortar Mix

1 part quicklime

3 parts sand

Slake the quicklime first, then add the sand.

Hydraulic cement, or mortar, is a cemented wall mortar that will harden underwater. It's not quite as strong as normal cement or mortar, but when you need hydraulic cement not much else will do. This is good for preparing swimming pools, building ponds, cisterns, or dams. It is important to note that your quicklime must be incredibly pure for this to work. Also, instead of using sand, we will be using crushed terra-cotta. If you don't have enough terra-cotta or really like your flowerpots, you can use fired clay instead. Either way, it must be crushed into a powder.

Hydraulic Cement Mix

1 park quicklime

3 parts crushed terra-cotta

3 parts aggregate

Slake your quicklime, then add your crushed terra-cotta and aggregate

Hydraulic Mortar Mix

1 part quicklime

3 parts crushed terra-cotta

Slake your quicklime, then add your crushed terra-cotta.

 

I'm going to build a concrete Darth Vader statue. But you can build a castle, or dam, or something useful like a patio. Whatever you build, please tell me about it. As always, I hope this tutorial has taught you something and sparked your imagination. I hope you put to use.