It is hereby disclosed a method to print on porous substrate by a printer comprising: a print zone; a conveyor to receive a porous substrate on a loading zone and to move the porous substrate along a transport direction between the print zone and the loading zone; a print engine positioned on the print zone for ejecting printing fluid towards the porous substrate; wherein the method comprises ejecting printing fluid towards a front side the porous substrate and, by a controller, activating a vacuum source as to exert a vacuum on a back side of the porous substrate being the vacuum exerted while the porous substrate is within the print zone.