We had a two rooms made into one, and a doorway plastered over which is now part of the kitchen wall. Where the plaster has dried out there are a few hairline cracks. Tried to fill them with pollyfilla but they are so fine that it doesn't go in the cracks. Tried painting over them but they just come back. we want to sell the house in the spring, and although not major, they don't look good. Any ideas for covering them up?
polycell do a hairline crack filler that should do the job. Or you can get the smooth over paint that will work but you will need to do the whole wall.
The best way to deal with hairline cracks, (as long as they're not getting any wider) is to cut away each side of the crack to make a 'V' groove, then fill the groove with, e.g. Polyfilla and smooth it off.
Beware any filler that claims you do not need to sand afterwards. What they really mean is if you overfill it, the filler is awful at being sanded down, and you will have your work cut out.
I'd go along with the crack widening suggestion. Tended to work for me in the past. Shove the point of a screwdriver in there and run it down the hairline crack. Then fill it with filler and sand down. Finally paint over the wall.