S.C. Code Ann. § 29-6-50

If a periodic or final payment to a contractor is delayed by more than twenty-one days or if a periodic or final payment to a subcontractor is delayed by more than seven days after receipt of periodic or final payment by the contractor or subcontractor, the owner, contractor, or subcontractor shall pay his contractor or subcontractor interest, beginning on the due date, at the rate of one percent a month or a pro rata fraction thereof on the unpaid balance as may be due. However, no interest is due unless the person being charged interest has been notified of the provisions of this section at the time request for payment is made. Nothing in this chapter shall prohibit owners, contractors, and subcontractors, on private construction projects only, from agreeing by contract to rates of interest and payment periods different from those stipulated in this section, and in this event, these contractual provisions shall control, provided the requirements of Section 29-6-30 and this section are specifically waived, by section number, in conspicuous bold-faced or underlined type. In case of a wilful breach of the contract provisions as to time of payment, the interest rate specified in this section shall apply.