Hi and welcome BatBastard 👍 , I don’t use tab very often, I just kinda guessed, and I looked through a few books and I think that’s what it is, what’s the song
I think you’re right, if it’s a bit cold or there’s moisture present it will get what looks like almost white patches on the surface, it can be nibbed back and re sprayed, maybe put a heater down there while you’re working 🙂