shady emulsion on new plasterwork

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Hi guys,
            This has been a problem for us plasterers with no definative answer i can give to customers. For example painting new skimmed walls over old sand & lime walls ceilings etc,, 3mm thickness shows patchy covering as if paint is scattering.no chance of plaster being not fully cured,say 4 weeks after skim,good opacity quality paint used all leading brands.no chance of plaster being over polished as this issue never happens on new plasterboard by same plasterer so the quality of finish is consistent.Can the pva below the skim producing some chemical etc,,, in areas.

As you know if a householder is painting new plaster ans this happens the tend to slap more paint on the area which can cause an build up of paint giving a poor finish to new work.As i said it tends to be more of a problem on sand & lime original backgrounds in houses then reskim on top.Regards

[rmichael]

Was the plaster primed before painting?

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no in uk paint used is emulsion eg dulux trade matt,macphersons,leyland,johnsons all good brands on tins follow instructions for new plaster,water down first coat,in usa you call it latex paint i think.
first coat a mist coat.british gypsum plasters used only good materials.uk painters have probably come across this when painting plaster in older propertys.

[rmichael]

I understand the logic but thinned down paint is not primer.. you need the sealing properties of a primer/sealer to stop the telegraphing effect you are getting which is likely caused by the substrate. I am not aware of which brand primers that are available in the UK but I am sure that primer/sealers are available, I'd give one a try on the next one... 

[sorted]

Yes you are correct it is the substrate causing problem,but i would guess a very large number of painters do not use primers on our new plastered walls in uk.never seen it and worked with loads.
Very good advice i can now give out new advice to customers how to paint these surfaces.
thanks for your help.