How to hide a hairline plaster crack?

[thirdlaw]

After we hung a large mirror in a newly redecorated room, a hairline crack appeared in the plaster on the wall. I'm after tips on how to deal with it. I still have the original pot of paint. I can fill it with fine surface filler, sand and paint, but will I need to paint the whole wall?

if you do what you have said, that’ll work.
using the original paint means you only have to cover the part you’ve worked on. Once the paint dries the crack and the work you’ve done will have disappeared. Good luck!

I think if you try to fill a hair line crack it will show as a thick patch over the crack.

I would cut a V shape each side along the line, vacuum it, and then fill it. There is superior filler you can use to - what is the name does anyone remember?

“Toupret” is the name.

Go on YouTube. Score out the crack to a v shaped groove, slap filler in, second coat wider, sand.

Re the paint, it depends on the colour. We’ve patched some bits successfully, others not so. It’s worse with darker paints. Stir the paint really well and you may be ok.

Sanding with fine sandpaper.

Depending on how old the paint is, the wall may have changed colour a bit. We have used the same paint shade when patching like this and were a bit surprised to find out that the wall had yellowed a bit over time. We eventually had to paint the entire wall to get a reasonable result.

I have just filled a couple of hairline cracks by putting polyfiller on my finger and sliding it along the cracks. It's worked really well! I am trying to get some tester paint to match the colour and see if it is enough, or if I need to repaint the whole wall. Disclaimer that this is not what a professional would do and I don't know how well it will last.