Putting a ceiling on the lounge room presents an interesting problem. The flue currently disappears into a ragged hole in the roof, and there is a metal collar thingy in the shed that looks like it’s supposed to cover the hole, but the slope turns the circular flue into an elliptical problem.
We’re not quite sure where the plasterboard is going to go in this picture. It might be above the shroud bit, below it, or it might cut through half way.
So after the furring channel went on we made a bit of a guide with some string.
It looks like a half way through kind of thing. At any rate, we need some kind of transition between the plasterboard, which will go at an angle, and the flue, which is straight up and down.
We decided after some discussion that the best idea would be an additional shroud that extends below the one that is there, and below the level of the plasterboard. We won’t try to make it flush with the plasterboard in any place, as it’s going to look like a bit of a hatchet job that way. Instead we’ll have a white tube extending out of the ceiling, and have it black inside so that the flue disappears into a ‘hole’. It should be dark enough inside so that the flue looks like it’s unsupported by anything, though the tube will sit snugly around the outside of the existing shroud.
We can go ahead and do the plasterboard as well. It needs an ellipse cut into it at the same angle as the roof.
With a bit of calculating (the roof is 24.5º from horizontal) and looking up how to use a compass and a piece of string to find the foci of an ellipse and draw it onto the board, we were able to get a mock-up going.
The idea was to put the plasterboard onto a little ramp thingy to get the angle right, then bandsaw the hole out. So a bit more trigonometry yielded some measurements, and we cut a piece of offcut hardwood to length and then across the diagonal.
It’s pretty good: we couldn’t really get the protractor to confirm the angle to within half a degree, but it’s surely close enough.
It quickly became apparent that the bandsaw was way too small to cut the whole thing at once, so we sliced the hole down the middle and did half at a time.
The first side went OK, but then doing the other side the hole was on the high end of the ramp and it wouldn’t go into the bandsaw. We had to flip it over and do it from the back. But then it turned out the hole wasn’t central on the piece of plasterboard, so it was offset by about 1cm when it was turned over again! Doh. We sliced a centimetre off one side of each piece to tidy it up, making sure it would still line up with the wall.
It’s also apparent that there’s no way we’re going to cut a hole out of a piece of plasterboard that’s any bigger than the one we were working with, so the mock-up became the actual piece we’ll use.
After that it was time to sort out the flue’s new shroud. We measured around the flue (83.9cm circumference) and bought a piece of galvanised sheet steel that was big enough. It was painted with pot belly black paint (mainly for the matte finish as opposed to its heat resistance, since the present flue shroud only gets warm with the fire going full pelt) then cut to size. We bent it around into a tube, clamped it and drilled and riveted along the length of the join. All that wrangling scratched up the paint so we gave the inside another coat.
We had to wait a few days for dry weather, since we have to take the flue cap off the outside in order to lift the flue out of the fireplace. During that process we discovered that the existing flue cap was totally rusted out – it fell to pieces in my hands as I took it off.
Setting that aside as a problem for later, we went back in and lifted the flue out of the fireplace, slipped the new shroud under it and let it all fall back into place. Up on the ladder we tested the new shroud around the old … and perfect fit! That never happens. Bonus.
Now we just need to fit the plasterboard pieces around it, select a height for the bottom of the tube to sit at, and lock it all in with a couple of screws.
Back outside, we can’t leave the top of the flue without a cap, so we rushed down to the pot belly shop for a new one. Easy as pie and watertight again.