Abstract. This research work investigates the bonding characteristics of metakaolin-based geopolymer mortar with Portland cement mortar by conducting several destructive tests such as the slant shear test, the split tensile test, three-point bending test, on mortar-to-mortar specimens. Other tests were also done to assess the flowability, and compressive strength at various ages (7, 28 and 56 days) for both Portland cement and metakaolin-based geopolymer mortars. Portland cement mortar substrates’ surfaces were prepared with two levels of roughness at the interface, smooth or rough, overlaid by Portland cement or metakaolin-based geopolymer mortar. Flow values for both mortars were found alike at around 17 cm. Compressive strength results revealed that geopolymer mortars exhibit superior values compared to Portland cement mortar. Slant shear tests results have shown that geopolymer mortars overlays, compared to Portland cement mortars overlays, exhibit shear strength with cement mortars substrates, at least 2 times higher, namely at early ages. Results have shown that substrate surface roughening improves significantly shear bond strength (up to 1.5 times higher) but does not contribute to the tensile bond strength. Split tensile tests and three points bending tests have shown better results when GPM is applied as an overlay on cement mortar. Overall, results showcased that metakaolin-based geopolymer mortar has extraordinary bond properties compared to Portland cement mortar for several conditions of mortar-to-mortar bond.