Bubbles and creases are caused by air bubbles underneath the paper and can be the result of uneven smoothing. This can be avoided by smoothing down the centre of the strip first and then smooth outward. Bubbles that form during hanging can be fixed by lifting the paper up around the bubble and smoothing it back down. If the bubble is not discovered until the wallpaper is dry, it will be difficult to fix without causing a crease in the paper. Bubbles may also be caused by a weak bond with the wall. Avoid this by allowing adequate time for “booking” in the preparation stages. “Booking” the paper activates the adhesive so the paper sticks to the wall evenly.