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I bought the same colour to what I already had because I didn't want to change the actual colour, I just wanted to freshen it up as it hadn't been painted in a while and was a bit grubby. And I didn't say it was the stores fault re the colour, I was saying that a huge tub of own brand cheap paint was a false economy, a smaller tin of Dulux (or similar) would have done a better job for the same price.
Its hard to explain what it is like but although I'm definitely no expert, this isn't the first room I've painted and I've not had the problem before. It even feels rough to the touch in places and it wasn't before. I'll have a go with the light grade sandpaper first and if no luck, might have to try that roller. Thanks x