Wood ash works best as a preventative not as a curative.
Permethrin powder should be dry, not wet. Get the spray kind to spray.
I have had good luck with Ivermectin cattle pour on for northern mite. The poultry dust slowed them down (noticeable upon contact), but I had a population explosion this summer due to extremely long dry warm season such that my normal poultry dust regiment was not keeping up.
Three treatments of Ivermectin, couple drops at base of neck, couple of drops at base of vent.
You will need to do that 7 days apart to get rid of most lice/mites as the adults are killed but the eggs will remain.
After first Ivermectin, the population was vastly smaller. Second treatment hardly any left. Third treatment gone and not back (yet).
Clean out coop very well, spray with deterrent. Permethrin spray is most effective but I've had good results with Orange Guard (orange oil). Then sprinkle poultry dust...either permethrin or sevin...dry underneath bedding so that it will stay dry.
Then keep an eye out for the next couple of months.
If it is red roost mites, you will need a different treatment plan as those are especially resilient.
Edited by Lady of McCamley - 11/13/15 at 9:40pm