MDF Wall String

[curium]

I've just sanded down the skirting alongside my staircase as it was stained (or varnished, i can't tell). I've sanded back to bare wood and it feels furry and has no grain.

I'm wondering if this is MDF? I thought the wall string was a structural component so am wondering if it's normal practice to use MDF here?

 

[big-all]

mdf is not as strong as wood so would either have to be about 50% thicker or more likley screwed to the wall at least 2 times along its length which is less than normal at 3 to 5 times

risers and sometimes treads are mdf but i have never heard off a mdf string???

 

[Deluks]

Could have been stuck on afterwards.