Dusty plaster skim even after weeks

[egamar]

We've just had two bedrooms, hall stairs and landing skimmed over old plaster which was a 50yo mess of patches, different levels etc). Done by a FMB member so shouldn't have been a bodge. The walls in question took a LONG time to dry compared to the rest of the work .....

The plaster in both bedrooms is very dusty - the dust keeps coming, no matter whether we brush it off or not; I haven't tried a damp cloth yet, it just seems that the surface isn't "hard". The plaster in the HSL is not at all dusty.

We intend just to emulsion the walls - does this mean we ought to seal this new skim finish before we do, or will the paint do the job?

Any tips will be very welcome, it doesn't seem right, but I imagine it's not uncommon.

 

[Richard C]

Did the same plasterer do the bedrooms & the HSL? Do you know what plaster was used, was it just a finishing skim or was base plaster applied first? How flat is it & what does it look like generally; if you’ve employed a tradesman it should be perfect!
The finish shouldn’t be dusty & certainly shouldn’t be soft when you push your finger nail into it; it should be nice & smooth & leave barely a trace on your finger when you run it across; are there lots of rough, milky looking patches? It’s difficult to say without seeing it but it sounds as if they may have used too much water & over worked it when finishing off. If the dust keeps reappearing & it's soft, the surface is not bonded & it may never be any good!
A skim shouldn’t take long to dry out & can be over painted after just a few days; don’t seal the plaster or the paint won’t stick, just apply a couple wash coats of emulsion diluted around 20-30%; let this dry & then you can apply full coats.

 

[joe-90]

I agree with Richard. Sounds like he was too late going back to it and attempted to reconstitute it. I doubt it will ever be any good now.

 

[egamar]

Same chap did all the work. He did put two coats on, but I don't know what 'type' of plaster he used for both, (although ISTR there were two different types) and he did PVA the walls first. The HSL and the internal walls of the bedrooms are fine, it's only the external walls of the two bedrooms that are a problem.

As I say, the dusty walls took ages to dry and I do remember them being very thirsty when I painted over the wallpaper that was previously there.

I have a feeling they could have been damp with water 'wicked in' through and exposed end grain of a joist sized wooden construction which was part of a narrow sloping tiled run off construction (bit difficult to explain).

The plaster (dusty and not) all looks pretty much the same, it's only when you run your hand across it that you notice the coating of dust from the 'problem' walls and nothing from the 'sound walls'.

I don’t think it’s a fault in workmanship (although he over-ran, not being the fastest worker) and was in a bit of a hurry to get away and made a bit of a pig’s ear replacing architrave and stuff, but I can sort that.

If it’s just a matter of a more dilute sealing coat and more of them, no problem; just a bit concerned about ending up spreading a sludge of plaster dust across my nice smooth walls as I roller the paint on (or rather as the Mrs does),

Thanks