I've painted a hallway/landing walls & ceiling which were plastered 8 years ago(!) without watering the paint (matt emulsion) down. What effect, if any, will this have on the walls?

You only need to water the paint down,to mist coat, i.e. new plastered walls ,but we are not doing that here so ,write in this case a good little light rub down, and two very nice coats of Emulsion should be fine

The effect it could have could cause the paint you have applied will start to flake and it wont bond to the walls very well

Hi this will have no effect on the walls at all the only reason why you water down the fist two coats is becouse freashly plastered walls will soak the moisture out af the paint so painting with watered down paint will but the moisture back in to the wall and give you better coverage hope this helps

the finish will be uneven ,most new paints now do not cover very well,so it is better to apply a mist coat first followed by a further 2 coats .This should provide a smoother finish and be more durable