How to apply wallpaper over styrofoam?

Question

I live in an attic, and the head part of my bed is in a corner where the roof slope, an outer wall and the wall to the neighbour's unheated attic meet. After a few winters of waking up to the feeling of the roof slope sucking the warmth out of me, I got a pack of polystyrol inner wall insulation. Unlike traditional styrofoam, it is a homogenous foam on the inside, similar to polyurethane foam. On the outside, it has a matte finish with a very fine paint-like structure.

I nailed the plates to the wall, right over the existing structured wallpaper. Then I filled the seams and the nail heads with acrylic caulk. Now I'd like to give it a finished look.

I feel adventurous enough to try a wallpaper. I have never applied wallpaper before, but it seems that the new cellulose-fleece-backed type is very easy to work with.

The problem is that the Internet tells me that regular wallpaper glue won't stick to regular styrofoam. I didn't find information specific to the glue for cellulose-backed wallpaper, or about this finished styrofoam. I also found the information that wallpaper can be applied to styrofoam in the following order:

• a layer of styrofoam glue, left to dry out
• a layer of underwallpaper soaked in normal wallpaper glue
• a layer of standard wallpaper, applied in the standard soak-in-glue method

This information came from the site of Henkel, manufacturers of styrofoam glue which costs 7 Euros per kg, an amount which only suffices for 1-2 square meters of wall.

Before I pay for glue two times as expensive as the styrofoam below it and three times as expensive as the wallpaper above it, I'd like to know:

1. Is a base layer of styrofoam glue the only way to get wallpaper to hold to the styrofoam?
2. Do I really need an underpaper layer if I am using a cellulose-fleece wallpaper as opposed to a standard one? Does it help hold the real wallpaper to the styrofoam, or is it just to give a nicer look?
3. All articles I read agree that it is possible to paint over styrofoam using regular water-based inner wall paint. Could I paint over the styrofoam and apply wallpaper to the paint? It would cost three times less than the styrofoam glue.

This is what the caulked styrofoam looks like right now:

Answer 1

You should not do this. Foam insulation (EPS, XPS, etc.) needs to be covered with drywall in order to protect it (extend the amount of time before it melts) from fire. Otherwise you are risk of being exposed to toxic fumes and melting foam should you ever have a fire. Imagine molten foam dripping from your ceiling onto you - not a situation you want to find yourself in.

The correct "solution" is to drywall on top of the foam (using furring strips, or long screws into the studs), mud/tape the drywall, prime, and then apply wall paper using standard wall paper adhesives.

Answer 2

do you have drywall over in Germany? i would do a little framing (probably with metal studs, that's used in Europe), insulation inside, then drywall over and wallpaper over drywall.

Answer 3

Cellulose wallpaper glue works fine

I've just finished (two months ago) gluing polystyrene insulating tiles to my bedroom walls with normal wallpaper glue i.e. cellulose. Then I stuck on a layer of wallpaper with cellulose wallpaper glue and it has all worked perfectly.

So I do not think you need to use any special glues. If you 'size' (prepare) the tiles first by painting on a very thin, watery layer of wallpaper cellulose glue and let it dry, you get excellent adhesion with ordinary wallpaper adhesive. I am a perfectionist, and I can tell you that the end result looks excellent!

Answer 4

Going back to the original question, it is true that the glue that is activated on the back of pre-pasted wallpaper is probably not enough to make it stick to the wall. Most pre-pasted wallpapers come with instructions advising to SIZE the walls before wetting the wallpaper strip and THEN use a brush to add wallpaper glue (I can't remember if that is what it's called...quart size bucket of stuff that is thicker than the sizing but not as thick or sticky as Elmer's glue). I realize now that this was from a year ago, but oh, well.