I have spent a great deal of time working on this question yet, I have no solid answer to go on. I tend to enjoy acquiring a skill set which would be very useful come TEOTWAWKI (the end of the world as we know it). I am far from a prepper, however I still entertain a slight possibility and see no problem with learning how to do a little more than cope. These skills extend from knowing where to grow, gather, and how to store penicillin to simple things like a yeast starter 100% from scratch. Brewing and distilling are also handy because it makes a great trade item. These are all things you never see in the Walking Dead or any other TEOTWAWKI cinema. One of the more important skills I believe would be conjuring fortress walls from rocks in the form of a little thing we know as concrete which we all take for granted. Now I could mix portland cement and filler with some water all day long and make a pretty cool fortess, but seriously. All the home depots in my state wouldn't have enough quick rite for that. So today I wan't to know what general rocks and minerals (that you can find in nature) can you combine to make cement. I know there are all kinds of fancy names for these, but what I really need is some good old generalities. Tell me to go outside grab a handful of clayish dirt, but it in a kiln with some lime and grind it up. I'm not looking for top of the line stuff here, this just needs to be able to hold a general form for a few years and be a little bullet resistant. This is for a crude fort, not the tallest building in the world or the hoover dam. A simple mortar would also be nice, although there really aren't any stones around to put together, bricks aren't super hard to make with as much clay as we have in our soil. So join me and maybe I will put together an instructible on all the skills you actually need but don't have!