How do you fix holes in the wall after a window replacement?

[Högsma]

We have replaced the windows in a cabin built in 1934. There are holes in the wall around the new windows that need to be fixed. In the holes are thick boards of some old insulation material with paper on the outside. Would it work to cut away all the existing material and fill with something like Easy Filler? If so, would you then need to put pieces of cardboard on top, as was done before, in order to paint and wallpaper?

 

[Högsma]

We have replaced windows in a cabin built in 1934. There are holes in the wall around the new windows that need to be repaired. In the holes, there are thick boards of some old insulation material with paper on top. Would it work to cut away all the existing material and fill it with something like Easy Filler? If so, would you then need to put pieces of paperboard on top, as previously done, to be able to paint and wallpaper?

It should be "all the loose material"!

 

[MathiasS]

It looks like you have a layer of masonite with paint on it and then a fiberboard called tretex underneath.

Personally, I would tear away this mess and install drywall on the walls instead. Maybe some insulation depending on the circumstances. You also need to frame the window on the inside.

Trying to use some sort of filler sounds like a slapdash solution that will never be good or even half-good.