Water based stain blocker advice

[venys]

Hello, hope someone can help as don't want to wait until Monday for advice from the shop. I have removed wallpaper from our bathroom ceiling and underneath was a paint or adhesive but with large patches exposing the raw plaster underneath. I had filled and sanded these patches and then we put a water based stain blocker on the whole ceiling today. But there are a couple of patches that have peeled away immediately. One where I think I had filled and one I don't remember filling so possibly on this paint. The patches are back to the raw grey plaster. Can anyone tell me why it is likely to have flaked off? I am unsure if this plaster is primed (I know I have clear plaster primer in the garage so not everyone uses coloured mist coats). Or could it have been these patches weren't clean. Either way should I refill and put stain blocker on again?

Is the ceiling dry?

It's possible it wasn't at the time of painting as oH had a shower about 3 hours earlier. But one patch is furthest from shower if that means anything?!

You say the plaster is grey. How old is the house?

You need to get an effective extractor fan fitted to suck out the steam, during and after every bath or shower, and it will take a week or two of good ventilation, no steam, a heated room and an insulated ceiling before it is fit to be patched.

Thanks for your advice Piglet John. Absolutely no chance of doing that on the ceiling. We decided not to fit an extractor fan as it would mean taking apart the whole bathroom - will cost £££ and more to the point will take too much time. We have a window and a radiator. The insulation is not great in the area either as much has fallen down in the loft above..nor is the bathroom above watertight so we don't use it unless it's an emergency. We have young kids and not much time, so have decided against fixing bathroom above for the moment as I can't deal with the stress of builders / delays etc at this time. I cant adequately supervise. The house is 1930s but not sure when ceiling was skimmed last. We are going to get a plasterer in to do some other work soon. Should we just skim over with newer gypsum or will we have the same problem? Could hire a dehumidifier?

Why would fitting an extractor mean taking the whole bathroom apart? It won't at all - the electrics can be run in the loft space above and the inlet can be in the ceiling and vented through a roof tile vent. Not fitting an extractor could very much be a false economy.

Just realised you've said there's a bathroom above this one which isn't watertight. So ignore what I posted about an extractor, but the leaking bathroom above is likely to be the cause of your ceiling problems in this bathroom. Find the leak and fix that - even if you aren't going to use the bathroom above.

Yeah we only used it recently when we had some work done to the family bathroom. So yes it could be a source of damp.(we had to put down polythene on the floor). But I know to fix the bathroom above needs a total refit, remove wall and put in new rigid insulation. If I wanted it done properly, remove the whole outer wall and extend the loft as it is an old loft that doesn't extend the full width of the house like newer ones do and it is also wonky!! There aren't leaks as such, it's the floorboards that have gaps in them I am reluctant to just patch it with some flooring in the meantime though if we were only going to pull it up again in the future. We still having problems with works done three years ago on the ground floor and wayward building control people and builders - so it ain't going to happen for at least a year or maybe never.

Actually you guys are right, I think where the patches have failed and peeled away was when we were using the bathroom above and I patched a little bit. I might wait a bit before patching again.

The grey made me think of filler, which is more likely to turn to mush when wet.

You could scrape it out and use a plaster product.

You are wasting your time if you don't cure the wet first.

I am pretty sure the grey is not filler - it's old plaster seen throughout the house. I will do my best to get the ceiling dry before trying again. But will be prepared if it doesn't work too.