Owner’s duty.

After notice shall be filed by said party employed under the original contractor and a copy thereof served upon the owner or his agent as aforesaid, the owner shall be bound to retain out of any subsequent payments becoming due to the contractor a sufficient amount to satisfy any indebtedness due from said contractor to the said subcontractor, or other person so employed by him, secured by lien as aforesaid, otherwise the said party shall be entitled to enforce his lien to the extent of the amount so accruing to the principal contractor.