Weird cold spots on eaves after skim?

[sealed]

Had walls skimmed 4 weeks ago - curved wall (1930s house) to ceiling has these patches which I think is where it hasn’t dried.
Mist coated today and it’s not adhered/soaked in to these patches.
Should I just wait much longer?
Is it worth going in the loft and putting insulation right into the eaves? Would this help? Need to get on and decorate these rooms.

I suspected it might be due to lack of ventilation but a roofer (without going into loft or looking at this) said that if I don’t have felt in the loft there will be plenty of ventilation. Loft doesn’t have eaves vents so I wonder if it is just that ventilation isn’t getting to these eaves??

 

[sparkwright]

If the plaster still had dark, damp patches, then you shouldn't be painting them.

If that area needed more plaster, for whatever reason, it would take longer for those to dry.

Some form of heating could have hurried up the drying process.

It may well be you have some kind of cold spot there, we can only guess.

It certainly wouldn't do any harm to fit insulation above, IMO.

 

[sealed]

If the plaster still had dark, damp patches, then you shouldn't be painting them.

If that area needed more plaster, for whatever reason, it would take longer for those to dry.

Some form of heating could have hurried up the drying process.

It may well be you have some kind of cold spot there, we can only guess.

It certainly wouldn't do any harm to fit insulation above, IMO.

Thanks. Heating has been on. I’ve put insulation up there today so hopefully will dry out soon

 

[opps]

open the windows as well. Air flow is even more important than temperature (both help though). I discovered that many, many years go when I was young- I had to, unexpectedly plaster a wall. It was snowing outside and I complained to a mate about the fact that the plaster was still wet after 10 day, He recommended that I open the windows, the increase in the rate at which it dried was stunning.

I too think it is likely that that the plaster (at the thickest points) was still wet

 

[Chivas69]

Is it a lashing of pva? This is often see through on the must coat. Make sure it's dry and give it a light sanding. Then try again with the mist coat. It should then take the top coats.