Mastra was born in the neighborhood of La Aguada of Montevideo and he spent his childhood on humble stages of Parque Rodó, then called Parque Urbano (Urban Park).
When he was a kid all occasions were good for him to sing. The public asked him and he agreed.
His facet as an author needs to be highlighted.
His creations were soon included in the songbooks of the most important orchestras and singers.