Leave it on for at least 10 minutes and then spread the foam again with the brush and rub it in well. It is advisable to let the vinegar purification soda solution sit for up to 30 minutes and then brush a little more until the limescale seems to have disappeared.
For stubborn scabs that have been present for a long time, this is a wise procedure. However, with regular care, the effort is even lower. You can also use only white vinegar, but only if the situation is not too "serious".
