You can add the ashes to a sand bath, but would need to mix it with sand or dirt. There are some older threads you can search on BYC, but here's a link from Poultry Magazine with a formula on how to use it:
I dump the cooled ashes from the woodstove in a corner of the coop. I use the deep litter method, so the birds work them right in and I'm not so worried about them inhaling ash.I've always heard the ashes are good deterrent for external parasites...I've never had a problem.
Do a search here on deep litter method....it's basically where you pile decomposable material as your bedding in the coop and run it similar to an ongoing compost pile.