Hi mojopin, these sound like you are doing the painting in strips and overlapping each piece. If you are painting a whole wall with a brush you will need a brush about 4ins in size. Start at the top and do whole strip along the top of the wall about 12 to 18ins deep then go back to where you started and do same thing again and carry on until you reach the bottom. You need to work fairly quickly as you need to keep a wet edge or you will get the lines you talk about. I find it's easier to use a roller as it will be quicker to use and easier to keep a wet edge. If you do decide to get a roller go around the edge of the wall first then fill in the main area after you have done this. Good luck.
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