Puerto Rico was devastated by Hurricane Maria on September 20, 2017. Due to a delayed and insufficient official response from the local and federal governments and other aid agencies, the effects are still crippling more than a year after the event. When official response networks failed, communities often engaged in informal reconstruction processes to facilitate their recovery. This research seeks to explain why certain communities were effective in reconstructing on their own and uses social capital theory as the theoretical framework. This study was conducted in four municipalities in Puerto Rico (Adjuntas, Barranquitas, Loíza, and Utuado). A mixed methods approach was adopted in this study which included interviews (N=31 with community members, local business owners and stakeholder representatives in Adjuntas, Barranquitas and Yabucoa) and door to door households surveys (N=163 in Loíza). Data analysis included qualitative analysis of the interviews where the researchers coded main social capital themes (e.g. linking, bridging and bonding). Data analysis of surveys included chi squared tests evaluating the frequency of social capital forms and informal reconstruction. The results show a significant relationship between informal reconstruction with bridging and linking social capital. Results will contribute to theory and practice of social capital mobilization in post disaster recovery contexts especially in the context where housing is ineligible for official aid. Understanding informal reconstruction through mobilization of social capital will contribute to identifying how communities can use resources available to them in times of crisis and need.