Separation of concerns allows the achievement of important benefits in all phases of the software development life cycle. Thus, it is possible to take advantage of this technique with the consequent improvement of the understanding of the models. However, conflicts of different types may be produced when concerns are composed to form a single system, due to the same fact of having them managed separately. Additionally, this problem is increased by the number of people needed to deal with large projects. This article is focused on the composition of concerns in structural models, in which each concern is realized by an individual class diagram. The same classes are present in several diagrams, although with different members and relationships, due to the specific nature of the concern they realize. In systems of medium to high complexity, the intervention of more than one analyst is required and, because of the working styles each one might have, many other conflicts could arise when all diagrams are composed into only one. In this paper, we present an experience in which four systems analysts elaborated six class diagrams which belong to a single system and we expose the conflicts that occurred after the composition of the diagrams. After the analysis and classification of the conflicts, a set of modeling agreements and recommendations was elaborated in order to reduce them. Then, the models were rebuilt and composed again, with a significant decrease in the number of conflicts detected after the second composition.