Positioned within Social Design (design motivated by social demands and not by the market), this paper reports on PhD research focused on uncovering the relationship between informal-mutual learning and community-based co-design. As the study progressed, following an ethnographic approach into a pilot study and two case studies, I raised awareness of a collective learning process supported by the co-design situations which engaged different people, all learning from each other, usually unconsciously. As a result, I developed a theoretical framework, based on Cultural-Historical Activity Theory (CHAT), one capable of itemising a myriad of entities and interactions entangling in co-design situations, describing their relationships and functional dynamics. The framework visualises this relationship and draws attention to the relevance of informal-mutual learning as an essential synergy towards achieving collaboration.