I painted the walls four months ago, using Homebase/Dulux Emulsion (whatever I hadn't used up). I treated several hairline cracks beforehand with flexible filler out of the gun (the kind that is overpaintable after about an hour). But because the cracks were really hairline ones, I just smeared the filler on with a palette knife, forcing it into the crack, then wiped over with a damp sponge.
Now the cracks have reappeared. What can I use to prevent this from happening again? Maybe I *should* have used the gun and really forced the gunk into the crack. However, they really ARE hairline ones!
Cheers!
MM