We have a large, open shower that is tiled in 2"X2" tiles. About every 8-12 months the drain starts running slowly, and I unscrew the metal drain plate to remove the hair that invariably has built up. That is not a big deal, but what is also slowing the drain is a very white mineral(?) buildup that accumulates like a hard coating around the drain opening and down the ABS drain pipe so that there is a mixture of this material and hair cemented into it. When I do the maintenance on this drain, the coating in the pipe can be up to 1/8" thick and go down about 6"-8" in the pipe. As the pipe goes down to the water level in the trap, the coating diminishes to nothing, and does not seem to be present below the water line.

I can take a screwdriver and chip it out pretty easily. It sort of looks like hardened joint compound (with hair mixed in!), but it's harder and more brittle. I can usually keep this stuff from falling down the drain because the hair holds it in place and I can pull the disgusting mess out with a long-nosed pliers. This hard material also builds up in a few of the tile grout lines leading to the drain, and it can be removed by scraping with a screwdriver tip, but is almost as hard as the grout.

My wife thinks it is some kind of soap or shampoo residue buildup, but I'm thinking it could also be some minerals in the water that slowly deposit over time after the water evaporates from the shower. We live in a large, metropolitan area and are on city water, so I don't think there is a big problem with the water supply, but I don't know. Our house is only about 8 years old, and the plumbing supply lines are all copper.

I'm ok with having to clean out hair accumulations every once in a while, but I'd like to figure out what this mineral-like buildup is, and what I can do to prevent it, or to remove it more easily than by physical scraping. Any speculations will be appreciated.

[This is cross-post from the Kitchens Forum. I didn't notice until after posting this in the Kitchen Forum that the Bath Forum is now split off. I generally do not cross-post, but wanted to cover my bases.]