Open seams may be caused by a variety of factors:
- Shrinkage during drying is normal with paper-backed products. If the surface is sealed, the glue may not always be able to absorb the tension which occurs during drying. This effect is strengthened by an impermeable top layer such as vinyl (the paste will remain moist for too long so that seams may become visible when it shrinks).
- If the paste is too weak, it will not be able to absorb shrinkage as it dries.
- The surface is too absorbent and was not pre-pasted well enough, so that the seams are unable to adhere.
- During soaking, the lengths were not laid correctly on each other and were not folded up, so that the edges dried too quickly.
- If the heat is too high before the wallpaper is dry (e.g. radiators, heaters or even halogen lamps placed too close to the newly papered wall). This problem can occur with both paper-backed and non-woven-backed products.
- We strongly recommend that the materials are allowed to acclimatise in the space or at least in similar conditions for at least 48 hours before they are used. Otherwise, there may be problems with the seams. Obviously, a roll that is hung immediately after being taken from a very hot or a very cold delivery van may react strangely.
- Vinyl is very sensitive to temperature fluctuations and this can even cause problems after several months if the surface has not been prepared perfectly.
- Plaster surfaces or layers of paint that do not adhere well may come loose and cause problems with seams because they are not strong enough to absorb tension in the wallcovering.
- Double cutting in the surface may also cause layers of paint or plaster to come loose, resulting in a visible or open seam.
- Generally, products with non-woven backing do not shrink as they dry. Some non-woven wallcoverings may still shrink a little, especially if they are subjected to intense heat when drying. In most cases, (stronger) paste will absorb this slight shrinkage.
- People are often inclined to push or brush open seams towards each other. Non-woven (backed) products will try to take on their original shape.
Seams may also end up on top of each other. This may be caused by the following phenomena:
- Paper-backed products: insufficient soaking times – the paper continues to expand on the wall.
- On sealed surfaces, there may be extra expansion after soaking.