Where'd you read that? A lot of folks use peat moss in chicken baths, either alone or mixed with other ingredients.Curious, I googled peat moss for chickens… it’s not recommended- something about the bacteria and it’s too clumpy.
Mine love just plain dirt, kicking and wallowing in it. I add wood and (junk mail) paper ashes plus paver sand, even vacuum cleaner dust. A 2 x3 spot underneath the coop is ‘their’ dust bath hole. But they create holes everywhere in the run with just dry straw too!
It's not clumpy in the slightest as long as it stays dry, which is possible in either super dry climates or in a climate protected spot. As I get a lot of rain I have mine in a plastic sand box so the chickens only get access when it's dry out, but they get super excited when "the pool's open."