Showing mould in the corner of the room.
Showing the same corner with picture added for scale.
After reading a few articles on insulation I decided to use this 2mm thick Polystyrene Veneer under the wall paper.
View showing the end of the roll clearly showing the 2mm thickness.
When purchasing this make sure the ends are not damaged or you will have a gap when matching the lengths.
After removing the old wallpaper and sizing the wall (this helps in hanging the wallpaper as it allows you to slide the paper into position easier) I mixed up the wallpaper adhesive and applied it to the wall not the polystyrene then cut and fixed the polystyrene into position.
Showing the 2mm polystyrene on the wall.
This shows the amount of thickness taken up on the skirting board which is not much.
After allowing it all to dry for at least 72 hours I applied the wallpaper onto the veneer.
Then it all went wrong.
The veneer started to come away from the wall in certain areas as the wallpaper dried.
This shows one position on a corner where the veneer is not stuck to the wall.
There was only one thing for it and that was to take the whole lot off and what a mess it made.
In the end I mixed Thermilate to the paint when painting the ceiling and the paintable wallpaper. http://www.thermilate.com/
I know this works as I applied it to a bay window ceiling and it stopped the condensation from forming.
My conclusions are that you have to mix up a very strong adhesive to stick the polystyrene to the wall.
Do not allow any gaps between the polystyrene and the skirting board otherwise the wallpaper will curl away as it has nothing to stick to.
If you take my hints above I am sure the polystyrene veneer would work as it did feel warm to the touch before I took it all off again.
Just as an update on using the polystyrene as a backing. I have used this on the wall below our bay windows and it has stuck perfectly. I mixed up a very thick paste and applied it to the wall then offered up the polystyrene to this.The lesson learned is to make up a good thick paste so that it is a very strong adhesive.