I have an interesting thing happening to my brick chimney. We noticed that two of the bricks, their faces, kind of crumbled off. Not the white powdery residue but actually powdered off in the same color as the brick. Looking for a reason why this might be happening. We live in Missouri (St. Louis). In the pictures the picture labeled “Brick 2” is what the effected brick looks like. The other picture is a typical smooth brick on our chimney.