Whenever work is done or material is furnished for the improvement of real estate upon the employment of a contractor or some other person than the owner and such laborer, mechanic, contractor or materialman shall in writing notify the owner of the furnishing of such labor or material and the amount or value thereof, the lien given by § 29-5-20 shall attach upon the real estate improved as against the true owner for the amount of the work done or material furnished. But in no event shall the aggregate amount of liens set up hereby exceed the amount due by the owner on the contract price of the improvement made.