Sealing chimney breast opening

[Al@n]

Gas fire has been removed, instead of bricking it up as it maybe reinstated in the future.

What could I use to seal the opening without causing damp, ventilation issues etc with the chimney breast.

Pic attached

 

[Wayners]

Thermalite blocks with sand and cement.
Cut easy with an old saw.
Fit a vent in the front to allow air to flow through or you will get condensation.
Plaster over smooth.

Easy to knock out if you wanted to

 

[Al@n]

Thermalite blocks with sand and cement.
Cut easy with an old saw.
Fit a vent in the front to allow air to flow through or you will get condensation.
Plaster over smooth.

Easy to knock out if you wanted to

It'll stick out like a sore thumb, as I don't have any spare wallpaper either.

Any other alternative options? I was thinking MDF with a vent or something to cover the opening...

 

[Wayners]

Do that then. Not sure how you are going to make tidy. Just emulsion the MDF I guess.