With their second album, Rio Grande Mud, ZZ Top uses the sound they sketched out on their debut as a blueprint, yet they tweak it in slight but important ways. The first difference is the heavier, more powerful sound, turning the boogie guitars into a locomotive force. There are slight production flares that date this as a 1972 record, but for the most part, this is a straight-ahead, dirty blues-rock difference. Essentially like the first album, then. That's where the second difference comes in – they have a much better set of songs this time around, highlighted by the swaggering shuffle "Just Got Paid," the pile-driving boogie "Bar-B-Q," the slide guitar workout "Apologies to Pearly," and two Dusty Hill-sung numbers, "Francine" and "Chevrolet." There are still a couple of tracks that don't quite gel and their fuzz-blues still can sound a little one-dimensional at times, but Rio Grande Mud is the first flowering of ZZ Top as a great, down-n-dirty blooze rock band.