I'm not sure what material was on the chimney before, I know it was individual planks. That material and the wood on the chimney was rotting and needed to be replaced. The same think happened in the front entryway and hardiboard was used and looked like what was originally up there. This new contractor used backerboard (I'm hoping I'm using the correct terminoloy). It was the same stuff that my tile guys used in the shower. He said they were out of the hardiboard at HD. I'm kind of a regular there, I don't see how this is possible looking back on it, but aesthetically it is just ok. I'n just wondering if it is going to function properly.