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Plastering over is usually better when the spachtelputz is firmly attached; removal is better when the layer is loose, the paint bonds poorly or the wall would become too thick.

You can paint wallpaper or put furniture against it once the paste behind it is dry; there is no fixed number of hours, because temperature, humidity, ventilation and the surface decide.

Painting over wallpaper only works well on paintable wallpaper: renovation fleece, glass fleece, glass fabric and woodchip (Rauhfaser) are made for it.

We advise against plastering over fibreglass wallpaper, because the plaster then hangs on the wallpaper and the old paste: removing it first and plastering afterwards is the safe route.

You can patch a crack in plaster if it has stopped moving and the surrounding plaster is still firmly attached; if the layer is loose or there are many cracks, replastering is needed.

Vinyl wallpaper has a plastic top layer on a paper or non-woven backing, which makes it washable and more stain-resistant than paper wallpaper.

Hanging wallpaper over wallpaper only works if the old layer is firmly attached everywhere, and even then we usually advise against it.

Before the wallpaper hanger arrives you hardly need to do anything: give us access to the walls, take pictures and shelves off the wall, and choose your colour in advance.

With glass fabric, pre-painted saves a coat; with glass fleece, according to Sigma, it does not: the advice there stays at one coat either way.

You work out how much wallpaper you need in drops, not in m²: the perimeter divided by the roll width, and the roll length divided by the wall height plus trimming allowance.