Removing strange stains on fresh plaster?

[Mr. Clueless]

Bit of a story...
We had our living room plastered & story very short, 1.5mtr of it needed to come off. We ended up getting the room done in a back to front order because we weren't going to have the ceiling done originally - so the ceiling was done last & these marks appeared after the ceiling was done.

Then the plaster was chipped off to 1.5mtr.

Now the job that the first guys did (wrong) is being rectified by another company. Soon they'll be coming to plaster the walls.
I spoke to one who i don't think is doing the plastering & he seems to think they're only going to be skimming so high, not bottom to top.

Q1) Will you see the 'joint' - where the new plaster ends & the old begins?

We would like the option of painting the walls instead of papering so don't want to see lines/joins through paint.

Q2) What are these marks & how do we get rid of them (other than plastering over)?

At the time i tried painting to see if it would get rid & it obviously didn't. I went with a 50/50 paint/water mix (Dulux trade supermatt i think it was) & then on top of this it was something like a 25water/75paint mix - & it still shows through.

Photo...

 

[roy c]

The stains maybe splashes of Sbr or pva, that the plasterers may have used at sometime! If you give them a light rub with a bit of "medium" sand paper you may rub them out. But go gently on them and try just to take the stain out.Hopefully they should just be on the surface.Good luck....

 

[chris_o]

Re will you see the join - if that rendered patch has been set at the correct level, any decent plasterer will be able to feather that in to the old skim and when painted you should not be able to see any join

 

[Mr. Clueless]

Thanks Chris.
I may just ask if they'll go to the ceiling with it to cover those stains - that'd be the easiest approach, although it'd mean more work for them.

As for the sandpaper - tried this approach & it didn't work unfortunately. Made the plaster look a bit crappy in parts.

 

[roughcaster]

If it was me, i'd bring the lower level out flush with Bonding plaster, let it set, then pva and skim "the whole wall",,, just as quick and easy, and it also guarantees you will "never" see the "new to old " joint in the wall, and it'll cover up the staining,, go for it!

 

[joe-90]

Before you do anything, place a long piece of wood at various places along the wall to see if the render is low or high. I can see this turning into a nightmare if you aren't careful. It needs the whole wall doing without getting PVA or plaster stains on the ceiling.