Coat 1st with primer when dry sand the rough edge really smooth and the second coat will take much better, This is the method i have used doing window contracts with mdf sils works perfectly.
Dont expect perfection unless you get a decorator to do the job.
I would use a sheepskin roller, and thin the paint 70/40 70 being water. if its waterbased masonry paint. 1 thin coat then a slightly thinned coat followed by a full coat should do the job.
Any pics? New plaster should absorb the thinned paint very very quickly, Hens why its thinned and a full coat wouls just lye on the surface. It will also look very patchy but its normal. 2 coats should clear that up no problem. Other than that i really cant understand what else could have gone wrong...
Is it bear timber? think its a threshold. Just a piece of wood to divide 2 rooms. Prime, Undercoat and a gloss the same colour as the wood work or stain varnish the same as the woodwork in either room.
The plaster should have had a top coat. 70/40 water. a vynal matt is more than enough i have used it for years and never had any problems even in my bathroom which gets really steamy when the shower is on. Proper prep should mean a good life expectancy.
Seems fine to me, 4 trades there, spark, plasterer, painter joiner. And a laborour. So all these mens time plus materials company costs soon mount up. I charged more for a couple of ceilings to be replaced with dampness.
It should take without anything, just wet the area 1st, It will be impossible to make it look identical so dont bother you will just irritate yourself. Just try blend as best you can. when set thin coat of paint and 2 coats or what ever looks best.
Dulux once is just a name to com people in my opinion, Get a proper undercoat and gloss. But would leave it a few days sand it down and recoat properly
