I have used barn lime for years, we used to use when we had a dairy farm to control moisture, and generally keep things cleaner.Here's a limestone ? for you. I hear varying opinions about using limestone to sweeten the deep litter in the coop, and to sprinkle a bit on the soil or DL in the run. I also hear that certain types of limestone are "too hot" and will damage the chicken's feet. Following that discussion, I picked up a bag of Agricultural lime, though I'd have to go down and look at it to know what it is specifically. I'd love your feed back on what is an appropriate grade/type of limestone to use in coop and run.
My flock is on layer feed as well (usually fermented). I offer oyster shell, though not all the time. When egg production goes up, or I see eggs with rough shells, I put out the OS. IMO, they will eat it when needed, and leave it if it's not needed. I think some birds do not metabolize calcium as well as others, therefore their needs are higher.
Excellent question.
We now use just the same in our chicken pens, on the concrete floor, on the poop board, in the nestboxes in the summer, and even in the run. I haven't seen any problems from it's use. It definitely doesn't burn and can help with keeping external parasites under control because of its drying ability. Make sure it's barn lime, around here the main brand is called Mighty White.