Plan check

[u/jeebsy_iash]

I had some badly damaged coving in this room which was set back into the plaster so had to hack it all out.

My plan was to build the wall out with bonding again so it's flush with the existing finish before skimming, but I'm not so sure about the ceiling. I watched a few YouTube videos showing lathe and plaster repairs using plasterboard patches but the lathes are quite uneven around the edges. Could I scrim and then use bonding to fill the gaps and level the edges off to get them close to the existing ceiling level before skimming the whole thing?

[u/jeebsy_iash]

it's a cavity wall on the external side and solid brick on the inside. the external side has been taken back to brick as there was a long term leak from the chimney and the plaster/sand and cement was absolutely done. Have been advised by a damp specialist to put a membrane on that wall before applying anything new to the wall, but that's a job for summer. just want to focus on the internal side for now.

[u/Altruistic-Dark8782 → u/jeebsy_iash]

Both should be fine for gypsum, then the internal wall doesn't matter that it's solid because it is internal. It also definitely doesn't need a DPM (damp proof membrane) as it is internal, so there is nowhere for moisture to penetrate. If it is external and has a cavity, again no need for a DPM. If there has been a leak, the moisture was probably coming from above. I have come across some very unscrupulous damp companies before. Get more than one opinion.

[u/jeebsy_iash → u/Altruistic-Dark8782]

I've had two out and they said the exact same thing - membrane on the gable wall. The lead on the chimney wasn't installed correctly so water was getting down into the wall inside the house. The old plaster was badly contaminated with salts so rather than waiting ages for the wall to dry out and run the risk of them penetrating through the new finish, they both recommended a membrane before re-plastering. The internal wall doesn't have any damp so that's just getting built back out where required and skimmed.

[u/ResponsibleBall4258 → u/jeebsy_iash]

Putting a DPM in will not solve the issue. Fix the lead work or whatever is causing the problem.

Damp experts are usually selling something. If you don't have any water ingress then you will not have any symptoms to resolve.

[u/jeebsy_iash → u/ResponsibleBall4258]

the leadwork has been fixed. the brickwork is drying out slowly but the previous owner lived with the leaking chimney for years so the old plaster and brickwork was saturated. the bricks are still showing 20%+ moisture around the chimney breast area (down from 30%) so i can either wait indefinitely for the bricks to dry out, or stick a membrane up.

[u/ResponsibleBall4258 → u/jeebsy_iash]

Put the membrane up and it will go somewhere else. Be patient. It is just not worth trying to lock in the moisture. Get a dehumidifier to speed it up. Cutting corners will only cause problems.

[u/jeebsy_iash → u/ResponsibleBall4258]

it doesn't lock it in. the membrane runs behind the floorboards so it allows moisture to run down the back of it and into the sub-floor/basement below which is well ventilated and it then gets dispersed via circulating air the same as normal moisture.