What the right way to fix this? This is the opening to a chimney, for the vent pipe for a water heater. I needed to enlarge the opening from 3 inch to 4 inch. You can see the round part on the left side.

opening for vent

I was cutting it larger with a hammer drill, and this piece came out (you can see my marking for the new size I need, and the holes I drilled to cut it):

broken piece of plaster and brick

The back side, has some brick and some plaster (and yes, whoever did this before me stuffed it with newspaper, which can still be read, 20 or more years later):

backside of broken piece

You can see how the broken piece fits in the wall:

broken piece held near wall

Should I glue the piece back in? Is there some kind of flat metal plate I can just put over the entire thing? Ignore the broken piece and just rebuild it with plaster?

  • Are you running a full pipe vent? If so, is this all just cosmetic? – isherwood Dec 13 '17 at 22:00
  • @isherwood I'm going stick a 4" metal vent pipe into the (new) hole. The pipe will not go any further than an inch or two into the hole, and after that it needs to be a chimney. (So I do also need to seal the new pipe into the hole.) – Ariel Dec 13 '17 at 22:03
  • 2
    Have you considered the local codes for the venting of gas appliances? Through masonry chimneys? – DJohnM Dec 14 '17 at 8:11
  • +1 on local code, call some well known professionals in your area, and gets quotes. The long term impact, of a failed DIY, is far worse, than the expense of knowing for sure, that it was done correctly, and safely.. – tahwos Dec 15 '17 at 1:19
  • @tahwos I just need to repair some plaster, this is not some complicated project. I am doing what was already there, which was done (badly) by a pro, so I'm not worried about codes - this is the exact same design that is found in homes all over the US. – Ariel Dec 15 '17 at 6:06

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