Jamieson, Fausset and Brown on Genesis 11:3

3. brick--There being no stone in that quarter, brick is, and was, the only material used for building, as appears in the mass of ruins which at the Birs Nimroud may have been the very town formed by those ancient rebels. Some of these are sun-dried--others burnt in the kiln and of different colors.

slime--bitumen, a mineral pitch, which, when hardened, forms a strong cement, commonly used in Assyria to this day, and forming the mortar found on the burnt brick remains of antiquity.