Flaking Crystalizing Paint - Damp?

[Alanhansen]

Noticed an odd patch of paint in my loft conversion. Had it newly plastered last spring and did a mist coast plus 2 or 3 coats of white emulsion.

Its in the corner with the wall the adjoining to next-doors loft. Been round to neighbours and theirs is fine on the other side of it though.

Anyway, it doesn't feel damp, but paint is flaking off, almost crystalizing if you can believe that. When i rub my hand over it i get covered in white dust, as it flakes onto the floor.

Could it be damp? Or the cold maybe? It wasn't like this before all the wet weather. Just have never seen damp paint react like this so was a bit confused.

Just wanted a bit of advice, or a second opinion before I plan on sanding it all back, then doing some oil based coats before another emulsion.

Any suggestions all welcome.

Untitled

• Alanhansen
• 9 Mar 2014
• 1

 

[foxhole]

Looks like a line of damp, probably roof leak or from that window frame.

 

[misterhelpful]

It is efflorescence which is caused by moisture within the wall so, as foxhole says, there has probably been a leak somewhere during the rain. As the wall dries out, the salts within the wall come to the surface and crystalize. Find the source of the leak and repair it, dry scrape and brush everything off and apply a coat of an alkali resisting primer to the bare plaster which should stop any more salts coming to the surface (don't introduce any kind of moisture until you have applied the primer). It isn't always necessary to do this but it can take several months (even years) for all the salts to come to the surface and as soon as you introduce the moisture of emulsion to the bare plaster they may start to reappear. The primer will help to combat this.

(I think that's actually the floor, foxhole. If it is, then it's possibly condensation, but a leak is more likely if it only appeared during the rain . )

 

[Flyboytim]

deleted - see below

 

[misterhelpful]

First find the cause of the water ingress, and prevent that, then refix a new section of board....

If it is plasterboard then a new section would be a better all round solution, provided the source is rectified, as the board is likely to have been damaged by a leak.

 

[Flyboytim]

It is efflorescence - made up of salts like sodium carbonate and sodium sulphate decahydrate.

If the wall has a plasterboard lining:
There has been water ingress into the plasterboard - either a roof leak, or condensation on the roofing membrane dripping onto the plasterboard which has dissolved these salts from the board manufacturing process out through the paper leaves of the board, lifting the paint and causing the powdery deposits as the salts dry.

First find the cause of the water ingress, and prevent that, then refix a new section of board, skim and redecorate. The old board will attract condensation and continue to effloresce, ruining further decoration attempts. Impermeable paints will mask dampness in the wall and continue to cause decoration problems - discolouration, and possibly mould growth.

If it is a solid wall, then the source of the salts could be in the brickwork of the party wall, which may need attention to the capstones and lead flashing if there is a parapet wall, otherwise a leak or condensation as above.