Thanks. Two questions:
1. Best way to check for damp?
2. Best wallpaper paste for this?
I should have said that the wallpaper appears to be fully stuck to the lining paper, if that makes any difference to the repair.
1.
Moisture meter – If you wanna be sure, grab a moisture meter. The Protimeter Mini is a solid choice, but even a cheap one off Amazon will do the trick. Just press it against the wall and see if it freaks out.
Look & sniff test – Easiest way? Just have a look. Peeling wallpaper, weird stains, or a musty smell = probs damp. Feel the walls too, damp spots tend to be cold.
Hygrometer – This is more for checking humidity levels in general. If your place is constantly above 60%, you might have a damp issue. ThermoPro TP50 is a good cheap one.
2. Something stronger than standard if it's fully stuck to the lining.
Border & Overlap Adhesive (Everbuild or Solvite) – Even though it’s meant for seams, this stuff is super strong and works well for reattaching sections of lining paper that have lifted.
Heavy-Duty Ready-Mixed Wallpaper Adhesive (Solvite Extra Strong) – Since your lining paper is still intact, a proper wallpaper adhesive should work fine. You might need to gently lift the affected area with a thin knife and spread some behind it.
PVA Glue (Diluted, 1:4 with water) – If you’re in a pinch and don’t wanna buy special glue, PVA can work as long as you don’t go overboard—too much and it’ll make the paper too rigid.
If the edges are loose, use a small brush or syringe to get the glue behind the lining paper. Press it down with a clean roller or cloth, then wipe off any excess. If it’s a big section, you might need to score it slightly and reapply a fresh layer of adhesive underneath.
Might be worth checking for damp behind it too—if the lining paper has started to lift, there’s a chance moisture is the culprit.