We introduce a construction of adding cells to a CW complex preserving homology groups. As applications, we recover the following cases: Quillen’s plus construction, Bousfield’s integral homology localization, the existence of Moore spaces M(G, 1) and Bousfield and Kan’s partial k-completion of spaces. We also use it to generalize counterexamples to the zero-in-the-spectrum conjecture found by Farber and Weinberger, and by Higson, Roe and Schick.