Upon the sale or conveyance of an apartment, all unpaid assessments against a co-owner for his pro rata share in the expenses to which § 55-79.13 refers shall first be paid out of the sale price or by the purchaser in preference over any other assessments or charges of whatever nature except the following:
(a) Assessments, liens, and charges in favor of the Commonwealth or any municipality for taxes past due and unpaid on the apartment; and
(b) Payments due under mortgages duly recorded.
1962, c. 627, § 15.