This is why it’s important to really thoroughly clean the walls of old wallpaper paste. Jennie painted some test patches yesterday, and they looked like this:
You can faintly see the pattern of the old Anaglypta underneath. We had this all over the wall and I was kind of hoping that it would just disappear under the paint (though I knew it probably wouldn’t) as I had already washed the walls twice with sugar soap and sanded it with the random orbital and didn’t really know what else to do about it. As a final attempt, went with a bucket of hot water with washing up liquid, vinegar, and bicarbonate of soda, and if that didn’t work, just lining paper over the lot and hope it sticks well enough.
It worked a treat, softening and smearing the glue residue around, then it could be removed with the razor scraper. The sugar soap didn’t soften it or shift it in the same way at all, so I’m sure it’s not just the scraper alone.
Anyway, when I scraped the painted area, some bits came off a lot more quickly and readily than others! I’m sure that if we had left it like this and painted straight over, we’d have seen this pattern flaking off the wall in a few months.
We’re going to lining paper anyway now, as even with my really careful filling, it’s clear the surface isn’t really good enough to paint, but at least now I’m confident that it’ll stick and stay stuck.