Trust is crucial for modern organizations and in particular in cases of virtual and distributed work. In such organizations much of the communication is based on electronic media, and the collaborators often know very little about each other when they start collaborating. Due to geographical boundaries it often takes a longer time to build trust in such organizations, and in difficult situations there is a risk of developing distrust rather than trust. This paper is concerned with how trust can be developed in highly distributed groups, and the network-related mechanisms that are used to build trust under such conditions. Based on a comparative study of vocational strong ties (intense, work-related) in four distributed groups, the study suggests that groups with higher levels of trust have an integrating core of collaborators that connects to central employees at the involved local sites. In contrast, the groups with lower trust had moved in the direction of establishing dual core structures with fewer boundary-crossing strong ties. Three central trust building mechanisms initiated by the integrating cores are discussed including; immediate coordination, visualization of work tasks and moderating conflicts.