•Combined lime-cement structural injection grouts were designed.•Time evolution of the grout setting process was monitored by proton NMR spectroscopy.•The grout setting process is significantly slowed down relative to the cement pastes.•Compressive strengths of the grouts are appropriate for historical buildings repair.•Swelling agent lowers the compressive strength of the grouts to an unacceptable level. We present design and properties of combined air lime-white cement structural injection grouts containing 17.5% of air lime, 7.5% of cement and 75% of limestone filler, using white Portland cement. Time evolution of the grout setting process during hydration from early to late stages was monitored by NMR spectroscopy and compared to pure cement-paste control samples. The grout setting is significantly slowed down (by more than 10 days). The compressive strengths of the grouts were found in the range 1.5–2.5 MPa, making them efficient materials for the strengthening of historical masonry buildings in Slovenia.