I suspect not much can live off anything covered with concrete dust and residue. You're probably safe from mold. If it does show up, I've had good luck rubbing down molding leather with a vinegar dampened cloth.Thanks, I didn't know about that. I suspect there was some as they'd spent three years abandoned in the garden shed, most of the white is cement from when I bricklaying in them though . Time will tell to see how they hold up, the leather was like cardboard before I started so I didn't expect much, but it doesn't bother me really, I just thought I'd have a go as they were just so comfortable.