Undercoat

[misseh]

Hello everyone,
Hope someone can help...

Decorating at present, started on the first room which had some areas of flaking on the ceiling. Noted it was flaking and stripped the whole ceiling, on removal of paint there was no undercoat in some areas.
Re-plastered where needed and treated with 50/50 PVA mix.
Sanded all areas and wiped down all surfaces.
In the process of applying undercoat at present, in some areas the paint isn't adhering and has sagged even before drying and peeled off significantly.
Removed undercoat where it failed and repeated today, when the fresh paint hit the first coat paint, it began to bubble and peeling again... The area I have plastered looks great, no issues there it's just the old plastered areas causing problems.
Thinking of removing undercoat and going ahead with a watered down emulsion.
Any advice or ideas of the problem?
Any help would be much appreciated - thank you!

 

[Crystalclear]

Is this a buy to let premises?

http://www.sherwin-williams.com/homeowners/ask-sherwin-williams/problem-solver/peeling-cracking/

 

[Robbie uk]

DO NOT USE PVA !!!!!!!!!!!! Just thinned down emulsion is all that is needed to use on new plaster !!!

 

[misseh]

We ended up using 50:50 PVA Mix and watered down emulsion, then 2 coats of white emulsion did the job.
Looked at the undercoat product reviews online - looks like there's an issue with that type of undercoat. Everyone mentioned it peeling/sagging off. I had bought it in store and didn't know about these issues. Thanks for responses.