Preparing the walls

It is important to note that 80% of successful wallpaper hanging depends on preparing the walls.
To hang wallpaper satisfactorily, surfaces must be:

-Clean
For this, it is vital that you eliminate all traces of:
dust
-dirt, stains
-writing, level lines, graffiti
-paste residues
-old wallpaper
-wall coverings
-paint

The wall must be washed and rinsed, and left to dry for a day.

-Absorbent The wall must have normal porosity, in other words neither too porous (a porous surface) nor not porous at all (impermeable surface).
Both excessive and insufficient porosity undermine good adhesion

Check porosity using the “WATER DROPLET” test:
Wipe a wet sponge over the wall, applying pressure.

-Porous surface: Large stains and no droplets
-Impermeable surface: Droplets run down to the base of the wall, leaving no trace on the wall
-Normally absorbent surface: Large stains with droplets which run down but stop before the skirting board

How to treat surfaces which do not have normal porosity?

        • Impermeable surface
Usually, surfaces are made impermeable by old paintwork or paste. To make them absorbent, you therefore need to:
-         Sand and wash the wall
-         Apply a coat of primer undercoat

        • Porous surface
Mainly newly plastered surfaces. Porosity can be reduced by applying a primer undercoat compatible with the paste (see primer label):
-A glycerol primer + 30% white spirit
-Or an acrylic primer + 30% water
-Or Metylan 1200 by Henkel

-Dry and sound The causes of humidity must be treated and eliminated before hanging to avoid paste-drying complications and mould after hanging the wallpaper.
Walls must be sound. They should not be contaminated by any substance.

-Level Walls must be smooth, flat and uniform because wallpaper tends to highlight any unevenness. Some wallpapers are quite thin so it is possible to see differences in colour and even pencil marks through them.
Small cracks in the wall and screw or nail holes must be filled with a flexible repair product. Use a calico (an elastic cotton cloth) to fill large cracks or to reinforce corners. Finish with filler.

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