Continuous Inkjet (CIJ) printing relies on steering charged droplets accurately to the surface with electric fields. A vital component is the set of deflecting electrodes within the printhead that create these fields. Unwanted deposition of ink on the electrodes, known as build-up, is a concern for operators because it modifies the applied electric field, affects long-term reliability and requires manual intervention, but is not widely reported or explored. Here we report a laser-based high-speed visualisation technique to observe build-up and show it stems from small satellite droplets that break off from the main printed drops. We characterise the material build-up and reveal its nanoscale particulate nature. Combining the tracking with characterisation allows us to quantify the charge-to-mass ratio of these droplets. This study provides a route to understand the build-up phenomenon and will enable optimisation of the printing conditions and printing reliability.