Hello,as per your problem you have thick scales over scalp.this occurs not only in dandruff but there are other skin conditions which cause such type of thick greasy scales.in such conditions shampoos containing coal tar with ketoconazole preparations help.which should be used every alternate days.leave it on scalp for 10min and then rinse.if condition is severe other topical lotions like mometasone with salicylic acid should be used for certain period.
Next Steps
consult dermatologist for correct diagnosis of your condition and for management.