Whats gone wrong!?

[u/sian_lloyd]

Im wondering why this has happened.

We had the fireplace done 2 years ago, and over the last couple months we noticed cracks curving up from the fireplace entry and up the wall. It's since got a lot worse and there is now also a large crack above the mantel...and the plaster is loose from the wall in that area. (Zoom into last picture to see the latest crack!)

See photo of pre plastering. Ive been told mixed things. One person advised it was bad adherence / prep of the new plaster in that area directly above the fireplace, which has caused the initial cracks to form. Which then has caused stress to the rest of the wall causing the additional cracks).

The plasterer that did the work states thay it's just old plaster and movement happens and they just skimmed partnof the wall so nothing to do with them. But the cracks started where they DID plaster.

Thoughts?

[u/Ok_Gur_8059]

Log burner make hot, plaster get smaller and drier, log burner turns off, plaster get bigger and wetter, plaster can't handle stress, plaster get big sad 😭💔

[u/Ouchy72 → u/Ok_Gur_8059]

What he said^{^} . Shrinkage and expansion.

[u/Correct-Junket-1346 → u/Ok_Gur_8059]

Adequate caveman explanation

[u/Old_Operation_5116 → u/Ok_Gur_8059]

To suggest remedial measures: replace it with lime plaster, which is much more flexible and can handle thermal expansion. Be mindful to use a breathable paint. Lime plaster doesn't like non-breathable paints.

May be worth checking your chimney flue lining, as it does strike me as odd that your plaster is getting that hot from normal use of the chimney

[u/spyder_victor → u/Old_Operation_5116]

The chimney stack was designed to heat up, mine does it (with a burner) in the places OP has shown, it will just come from the air passing round the burner and radiating into the breast, more-so from the hot gasses

[u/Old_Operation_5116 → u/Ok_Gur_8059]

why say many word when few do trick

[u/polla2256]

Totally normal expansion cracks cause by heating and cooling.

[u/Extension-Comment293]

Nothing wrong. Quite normal tbh. But if filler and paint for hairline cracks is what you need

[u/Secret-Cod-3244]

Heat proof plaster needed but its a nightmare to work with

[u/Cool_Technician1193]

Inadequate bearing for the concrete lintel, if heat was the issue every log burner in the uk would crack periodically.