New Precast Concrete Sills & Copings Eroding

[Max Air]

Has anyone had experience with new construction (less than 10 years old) precast concrete sills and coping stones crumbling and eroding? I've seen two properties in the last year at which the sills at patio and front doors are eroding along the front edge. I'm thinking it has something to do with salts and freeze/thaw, but it seem pretty fast to have this level of deterioration. The sill in the first photo was installed around 2006 and is at a front door of a 3-story townhouse on an elevated front entry. The second photo is at a rear balcony sliding door which was installed in ~2002. I've also seen some coping stones with the same issue.

Click to Enlarge

49.78 KB

Click to Enlarge

44.02 KB

Also, I know they also install limestone sills as well but I've never been able to really tell the difference visually. Anyone have a tip on telling if a sill is precast concrete or true limestone? Thanks.