These are either poored concrete forms or super huge pavers and they've been here at least 20 year's... maybe a hundred, IDK. But they arent moving or setling anymore, 4 inches thick, and currently have a maximum of 1/2 inch of height difference between block's. I've never done a reface but obviously it would be wet construction. What do you use? Thinset? Thinking of facing this with 1/2 or 3/4 inch flag. I dont think it's nesessary to remove them.