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I would have liked to know the precautions to take to put a wallpaper on a wall already painted.

A painted wall is likely to constitute a "non-absorbent" background on which the glue does not catch (it is said that the background is "blocked." If the paint is very glossy (lacquer) it may be necessary to depolish it or to apply a primer (eg METYLAN 300).To know if the paint layer is a sufficient attachment surface, apply on a strong adhesive tape (type for packaging parcels): if pulling from a quick blow the paint is peeling, it must be sanded or stripped.

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