Seismic monitoring of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) requires a uniform distribution of detection threshold over the earth. By design, the Primary Seismic Network of the International Monitoring System (IMS) provides an appropriate coverage. In order to effectively use the cross correlation technique and the archive waveforms from the International Data Centre (IDC) in global monitoring we have introduced a dense (spacing of ~ 140 km) and regular grid of master events with high quality templates at IMS array stations. In seismically active zones, we populated the grid with real masters. For aseismic zones, we developed an extended set of synthetic templates for virtual master events. This set includes a few simple double-couple source mechanisms in 1D and 2D velocity structures as well as explosion sources of varying size and at different depths of burial. All synthetics were first tested in seismic areas and showed the detection threshold similar to that demonstrated by real templates. We have designed three versions of the grid: V1.0 with only synthetic templates, V2.0 with real masters added where possible, and V3.0 with grand masters added. Their performance has been assessed by full processing of a few data days and a direct comparison with the Reviewed Event Bulletin issued by the IDC.