Peeling emulsion paint

[jackthelad]

Hi
I am looking for some advice please from some of you guys with more experience than me.
I am having a re occurring problem with an internal wall. The wall was re plastered about a year ago, having previously had damp issues from a leaking roof. I have had problems with the paint peeling in the same area. I primed it with PVA and once dry gloss undercoat.
I don't think the area is damp as there is no sign or staining. I am wondering if salts or efervecence from the old brick underneath is the problem. I believe that a alkali resistant primer should be used if this is the case.
Any advice, comment or recommended product would be very much appreciated.
Thank in advance.
Tony

 

[misterhelpful]

PVA was a bad move but you may have been lucky by applying an ?oil? undercoat before emulsioning.

The damage is definitely being caused by efflorescence, and is because excess moisture is/was still in the wall. As this dries, it pushes the salts to the surface and causes the blooming problem that you have.
To remedy, you should dry scrape all of the loose material away and ensure it is dry. Apply a coat of alkali resisting primer, and allow to dry fully before applying any filler to even out the surface. Once dry, you can sand smooth, apply another coat of the primer over the filler and then you are ready to continue decorating.
This method will only work if there is no moisture still in the wall, so you need to be sure of that, otherwise you will be back to square one in a few months.

EDIT:
If you have any Zinsser Bullseye 1-2-3 Plus laying around, this also claims to work for efflorescence, but it MUST be the Plus version and not the standard 1-2-3.

 

[jackthelad]

Thank you for your prompt reply.
I used PVA as I thought originally the problem was damp coming through, and PVA plus solvent based undercoat would hold back any remaining damp and staining. Can you explain what effect using PVA has had on the problem.
I don't have any suitable product to hand, so will need to purchase a suitable primer, I only need a small quantity as this is the only area requiring attention. Can you recommend a suitable product? B and Q don't seem to have anything that mentions alkali resistance.
Thanks again
Tony

 

[misterhelpful]

I favoured Blackfriar's Alkali Resistant Primer, but it became hard to come by in the few years before I left the UK, so I started using Johnnstone's or Leyland. IMO, neither are as good as the Blackfriar stuff, but both should be fine if your damp issue has been fully resolved.

PVA isn't suitable for use with water based paints, and sealing bare plaster with it is a big no-no within the decorating trade because of the issues it causes with paint cracking and peeling. It's not that the PVA will have necessarily made your situation worse, but sealing any excess moisture into a wall, and creating a film that water based paints don't adhere well to is not a great idea. As I stated, you were probably fortunate to get your paint to adhere because you used an oil based undercoat.

More on the PVA subject here:
//www.diynot.com/diy/threads/mist-coat-or-pva-bare-surface-basics.425261/

 

[jackthelad]

Misterhelpful
Thank you for your professional advice, it is very much appreciated.
I have read your link, very enlightening.
As I say I initially thought my flaking was due to damp coming through and lifting the finish, the logic being to try and waterproof / seal the area.
I can see now the error I have made. I will do as you suggest , and hope the wall has dried now.
Regards Tony