A person who is not primarily in the business of making realty improvements and regularly employs persons for the purpose of repairing, maintaining or making realty improvements for his own use and who repairs, maintains or makes a realty improvement for his own use with his regular employees is not a prime contractor and is not liable for the tax herein. Source: SL 1984, ch 92 , § 7; SL 1985, ch 93 , § 1; SL 1988, ch 108 , § 7; SL 1988, ch 120 , § 3; SL 1993, ch 101 , § 2.