familiar implies "a familiar usage"
A brick (Un ladrillo) in a familiar usage, it's something heavy you have to carry, literally or not.
examples
cosa pesada y aburrida (familiar):
-El discurso de Obama/Fidel Castro/Chávez fue un ladrillo
The lecture of Obama/Fidel Castro/Chávez was long and tedious
heavy (familiar)
-mi nuevo móvil es muy ligero, el anterior era un ladrillo
My new mobile phone it's feathery, the old was big and heavy
You can say both in a familiar way, but it's not a proper word to write.
saludos