This article explains what to do with an open wallpaper seam.
The wall is wallpapered but some wallpaper seams are open. What can be done now to fix the mistake?
Although there is no way to close the seam after drying, there are several ways to significantly improve the result afterwards.
The main issue with an open wallpaper seam is usually that with coloured wallpaper the white background shows through or the white backing paper of the wallpaper is visible. Therefore, you should try to match the backing paper and the background with the open seam to the colour of the wallpaper. Here we have had positive experiences with coloured pencils or felt-tip pens as well as ink colour.
Conceal open seams with coloured pencils or felt-tip pens
Trace the seam with a coloured pencil or felt-tip pen in the appropriate colour. Important: Test on an inconspicuous area beforehand.
Conceal open seams with the help of an ink set or watercolours
Even better results are usually achieved with an ink set. Here, the seam should be repainted with a fine brush in the appropriate colour and the ink should be carefully dabbed on the wallpaper with a lint-free cloth. It is also very important here to test in an inconspicuous place first and let it dry!