I am building a box in the ground and need it water-proof.Whats the best mixure cement/sand, or should I use concrete?What differs cement/concrete? And how do you make it strong from cracking without steel enforcement?
Technically, cement is what hold concrete together; concrete is an aggregate of sand, cement (usually Portland cement) and gravel. You can use pure cement as concrete if you want to, say, to fill cracks, same way you might use wood glue to seal up cracks where pieces of wood come together. Generally, fully cured concrete is stronger than cement by itself. I need to know more about the backyard box to recommend a specific approach. How big, how deep, above ground/below ground...etc.
About the only suggestions I can give you is to put a descent amount of granite gravel in with the cement and to mix it a little on the dry side. If you notice, old concrete from around the 1940's and earlier tends to hold up better than newer concrete. If you look at the old concrete in relation to new concrete it has larger gravel in it and it has more granite gravel in it. You don't want to put gravel such as limestone in it. Limestone will cause the concrete to break up during winter. A trick I learned off of a friend of mine who worked for a concrete company is to mix concrete on the dry side. A dryer concrete mix instead of a soupy one will tend to be stronger and last longer.
