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

Like this: One of them

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.

MKII
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  • Is that on an old chimney breast, or just blank wall? – Tetsujin Feb 12 '23 at 11:48
  • I guess it could be. It does line up with the old fireplace downstairs. – MKII Feb 12 '23 at 12:48
  • I'd see if you can ascertain the thickess of that section between visible wall & 'whatever is next behind it'. Double -check by looking to see if any chimneys on the roof could roughly align with it [bearing in mind not all chimneys are straight, they duck around each other on different floors to all arrive in the same stack. How old is the house? What type, semi, detached, terrace, etc? – Tetsujin Feb 12 '23 at 12:48
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    Ah, your tweaked comment does suggest it's 'chimney' of some sort. The line around the hole hints that it once had a map-vent on it, which someone has previously covered over - ill-advisedly. – Tetsujin Feb 12 '23 at 12:50
  • The house is a terraced house, from the 1930s. The other hole is on the opposite side of the house, filled with old paper scrap. – MKII Feb 12 '23 at 12:52
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    Answer added. You should not seal it. It has to breathe. – Tetsujin Feb 12 '23 at 12:57

2 Answers2

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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.

Tetsujin
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    Could someone qualify why "it needs to breathe"? I have a discussed chimney in my place which no longer penetrates the roof, and I've been presuming that closing it off to prevent it venting basement heat to the attic was a reasonable thing to do, at least until I am ready to remove it entirely and reclaim the space. If there's a reason I shouldn't, I want to understand that. I could make that a new question but a clarification here might be enough. – keshlam Feb 12 '23 at 13:48
  • @keshlam - Added to answer. Short term, damp; long-term, damage to mortar. In the UK you need planning permission to remove the top of the stack entirely & seal up, so they would make sure it's being done to regulations - darned if i can find the regs, though :\ – Tetsujin Feb 12 '23 at 16:05
  • Removing the top of the stack was dealt with by my contractors. They didn't seal it, though. Since the stack is no longer supporting anything (that failed long ago and was replaced by a column), I'm not convinced I care about damage to the stack's mortar. – keshlam Feb 12 '23 at 18:19
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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".

Rohit Gupta
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  • "depending on what's behind the wall" - exactly. It looks like it used to have a map-vent on there, which would indicate it's an old chimney. You're not allowed to fully block those up, you must let them breathe, hence my comment on the OP above. – Tetsujin Feb 12 '23 at 12:03
  • Sorry, -1 for not first ascertaining whether it must be left to breathe. – Tetsujin Feb 12 '23 at 12:58