Concrete
Fortress Material
<&recipe>Concrete is a very hard and resistant composite material. It's cheap to craft and makes for an excellent use for the excess slag produced by the <link;crude_blast_furnace;Blast Furnace>.
<&partial>Concrete can be cut into slabs of varying thickness using a §2Stonecutter§r.
You can also use that machine to make slabs and stairs of concrete, as well as concrete tiles which are smoother and more polished.
<&leaded>Leaded concrete is a reinforced material, which is highly resistant to explosions. It may also afford protection against radiation, if that is something you worry about.
<&liquid>Liquid concrete can be produced in a <link;mixer;Mixer> by combining half a bucket of Water with §2Gravel§r, §2Clay§r and §2two pieces of Sand§r or §2Slag§r. When emptied onto the ground it will spread like water, before solidifying after some time.
<br>Multiple buckets can be used to fill a larger area by placing it at key locations. Note that if it spreads too thin, the liquid will dry into slabs instead of full blocks.
If the concrete dries while a creature is standing in it, they will be trapped and unable to move. You can also fill a <link;chemthrower;Chemical Thrower> with liquid concrete in order to create improvised platforms or immobilize enemies.