This is such an interesting point. When I was young my dad and I remodeled a 300 year old timbered home. Many people who had done the same had used foamed concr

This is such an interesting point. When I was young my dad and I remodeled a 300 year old timbered home. Many people who had done the same had used foamed concrete between the beams and used modern paint. The outcome was similar to what happened to your garaje. Humidity lead to the beams starting to rod. So my dad and I used clay bricks and used lime based plaster and colors. Much more similar to how timbered houses used to be. Not only did the work come out well, but working with those materials especially the clay was a great experience. Traditional mortar will mess up your hands if you don't wear gloves whereas working with the clay was like a spa treatment.