When roller or brush marks appear on the varnish, it may indicate that the varnish is too thick for the tool being used. To avoid this, it is recommended to use a roller with a thickness of 10mm so that enough varnish is applied to the surface. If the marks persist, it is advised to add a drying retarder to the varnish. It is also important to allow enough time for the varnish to spread and settle properly, especially on large surfaces.