Using too much paste or allowing the paste to get on the wrong side of the wallpaper is the usual culprit when there are paste stains along the seams of your wallpaper. These yellowish or brownish stains can ruin the look of a room if left alone. With a little elbow grease they can be removed, giving a fresh look to your wallpaper.
Dip the sponge in the warm water and begin gently scrubbing the paste stains. Start in a less visible area to make sure that the water does not damage the wallpaper.
Wipe the area dry and scrub again with the warm water. Continue drying and scrubbing until the stains are gone.
Dip a towel into liquid fabric softener and wipe down any stubborn stains that water alone isn't removing. Gently scrub until the stain is gone and wipe away with clean water.
Mix one part vinegar to one part water. Dip your sponge into this solution and wipe the entire seam area to remove any leftover streaks that will dull the finish on your wallpaper.
After affixing wallpaper, wipe the seams thoroughly with a wet sponge to remove paste residue before it dries.
Do not soak the wallpaper as this will cause the wallpaper to lift.