How to fill a brick sized hole in a brick cavity wall?

Question

I have found two brick-sized holes that were covered up by multiple layers of wallpaper.

Like this:

As I intend to paint the wall instead, I would like to fill them in.

I am not sure how to do it, though. Do I need to place a brick there? Is there a better way to go about it?

I am based in the UK, for what that's worth.

Answer 1

As comments seem to have ascertained it was once a chimney, you should not cover it. It needs to breathe.

Judging from the photo*, in times past it had been correctly covered with a map-vent though a more recent trend would see it replaced with an air-brick set flush to the current plastered surface. It can be painted to match, but shouldn't be sealed off completely.

*It's exactly the right height & dimensions to be a chimney vent & you can see it used to be covered with a map vent.

Why it needs to breathe - it prevents moisture buildup which can lead to damp penetration on the entire chimney breast & also helps prevent that moisture reacting with the old soot, causing a sulphate reaction which will attack the mortar.
Strictly, you should have the chimney swept first & cap the top of the stack with a 'rain hat' preventing direct rain ingress whilst still allowing it to vent.

Answer 2

A brick, if possible, maybe the best solution. Any other solution would require a lot of filler/plaster. A solution that has worked for me, depending on what's behind the wall -

• Cut a piece of wallboard (gibboard/plaster board) just larger than the hole.
• Drill two holes in the centre about an inch apart
• Poke a piece of wire through the front to the back and then poke it back to the front through the other hole. Twist it together.
• Apply some adhesive to the outside edge of the flat that's going to face you.
• Insert it diagonally into the hole (which is why you don't want it too large)
• Straighten it so it will cover the hole from behind.
• Pull with the wire so the adhesive sticks to the inside edge
• Push a pencil or ruler against the wall and twist the wires around it.
• Now the board will not move.
• Let the adhesive dry well.
• Fill the indentation with plaster filler roughly and let it dry (don't push too hard)
• Sand anything that's too high.
• Refill it a little finer and let it dry
• Sand again
• Refill it, overfilling it slightly with a flat tool such as a trowel
• Final sand after its dry _ Now you can paint or wallpaper it.

I have often used this to patch holes up to 2" X 4".