Cool OT sidenote about this. I live in an adobe house, and I wondered for a long time what the difference is between concrete blocks and adobe bricks, in terms

Cool OT sidenote about this. I live in an adobe house, and I wondered for a long time what the difference is between concrete blocks and adobe bricks, in terms of their physico-chemical structure. Adobe has comparable compressive strength to concrete blocks, but unlike concrete will dissolve in water. I always found this a bit mysterious. Turns out that the most significant difference is that in concrete (or any cementitious material), the important molecular bonds are covalent. In adobe the bonds are ionic. Consequently, adding water to adobe easily disrupts the structure by interfering with the ionic bonds (just as it when salt dissolves in), but does essentially nothing to the covalent bonds in concrete. Even cooler, perhaps, is that as the wet adobe dries out again, the same bonds will reform, and you get back to the original state again.