A　major　flaw　of　3D　concrete　printing　(3DCP)　is　its　weak　interlayer　bonding.　Consequently　mechanical,　bond　behaviors　and　durability　are　compromised.　The　shrinkage　because　of　excess　surface　water　in　the　extrusion　process　and　its　evaporation　promotes　the　reduction　of　interlayer　bonding.　In　this　study　a　novel　additive　mortar　based　on　calcium　sulphoaluminate　(CSA)　cement,　cellulose　fiber　and　limestone　filler　was　proposed　for　application　between　layers,　which　permits　extension　of　printing　time　interval　and　also　caters　for　breaks　in　construction　printing.　The　mortar　was　applied　on　substrate　filaments　whereas　the　overlaying　filaments　were　printed　at　60　min,　90　min　and　120　min　print　time　intervals　corresponding　to　initial　and　final　setting　times　of　the　3D　printing　concrete.　Its　effect　was　verified　through　accurate　measurements　of　interlayer　tensile　and　shear　bond　strength　on　cross　bonded　samples.　Microstructural　investigation　of　interlayer　structures　was　through　SEM　to　cater　for　both　EDS　and　XRD　to　study　hydration　products.　Results　suggest　that　the　proposed　additive　mortar　holds　water　and　utilizes　it　for　internal　curing　to　attain　overall　enhancement　in　early　age　hydration,　produces　expansive　ettringite　to　counter　shrinkage　and　generates　additional　mechanical　bonding　between　printed　layers　by　fiber　and　fine　aggregate　interlocking.　Interlayer　tensile　strength　was　boosted　greater　than　1.91　MPa　for　60　min　print　time　interval.　The　composite　could　possibly　be　utilized　between　each　layer　of　a　typical　3DCP　operation　to　improve　filament　deposit　and　stacking　process,　to　reduce　voids　and　longitudinal　flaws　and　to　enhance　durability　because　it　is　very　easy　to　manufacture　and　apply　while　its　constituent　materials　are　plentiful,　cheap,　safe　and　environmentally　friendly.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.