Plywood paneling provides a quick, affordable way to cover up old walls and transform the look of a room. However, it's often difficult to get perfectly tight seams between the 4 X 8-foot sheets. If there's any gap or space, the wall behind the paneling will peek out.
Here's an old carpenter's trick that can help hide imperfect seams: Hold a sheet of paneling in place and mark a vertical pencil line on the wall along the edge of the sheet. Then, paint a 2-inch-wide stripe down the wall centered on the pencil line. Choose a paint that matches the color at the edge of the paneling, which is often darker than the paneling face. A brown or black broad-tipped marking pen will even do for dark paneling. Now if there's a gap between the sheets of paneling —or if one appears in the future — the paint stripe beneath will effectively hide it.