Advice on Damp Patches on new plaster

maybe_tomorrow_2

Two queries on damp plaster. Thanks for your patience!

1.
I have a property which has a loft conversion, it is an end terrace and the gable end internal wall in the loft has been recently re-plastered although is showing several areas of damp staining/discolouration.

what could be causing this at such a high elevation? Could damp/water be getting down the stack or something and damping the brickwork behind the plaster?

Can these areas be dried out and if so how would i go about doing so, or would it require a full replaster? Assuming the source is found externally and fixed. perhaps chimney stack needs re built.

2.
there has been a new damp proof injection and re-plaster on ground floor several months back. our surveyor recorded some areas of high damp readings suggesting the damp proofing has failed. The company which did it said it takes time to dry although there are areas of damp staining/discolouraiton on the new plaster,

does this mean there is still damp getting through or is this common with plaster??

How long does a damp proof injection take to reach its full potential?

They did say that if the high readings still persisted in a few months time then they would come out and investigate. Does this sound like a normal response?

Thank you