I had to install two circular, 8" through-the-wall exhaust fans in our building's bathrooms.

#1.) Checked for plumbing/electrical/studs in the wall and area of holes-to-be...
#2.) Once #1 was cleared, drilled a series (and I mean SERIES) of small, 1/8" holes from the outside, going inward...
#3.) Knocked the inside of the hole out first, then worked toward the the 1/8" drill holes on the outer edge...
#4.) Snipped off the "chicken-wire" lath and bent the ends inward...
#5.) Being very carefull (and using a small level) and proceeding inside to remove the drywall in similiar fashion, I was able to match the two holes up elevation/azimuth-wise...
#6.) ...and with a "bit" of fine-trimming, managed to cut down on the amount of "shaved" drywalling needed to make everything match up properly.

With everything "dry-fitted" before final-fastening, I was able to mark the outline of the escutcheons and "water-proof" the interior/exterior facial-pieces when time came to fasten it all down for good. (I used clear "GE Silicone Sealant" as the outside/inside "fastener" of the escutcheons themselves...)

Neither one has ever had a chance to leak back into the building and there's no evidence of seepage into/behind the exterior wall.

Taking the time to drill the holes was the biggest part...but not rushing any of it made for a very neat install and not having to come back afterwards to "re-stucco" the job.

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M. G. Burg
'10 - Dakota SXT - Daily Ride / ≈ 172.5K
.'76 - 450SLC - 107.024.12 / < .89.20 K
..'77 - 280E - 123.033.12 / > 128.20 K
...'67 - El Camino - 283ci / > 207.00 K
....'75 - Yamaha - 650XS / < 21.00 K
.....'87 - G20 Sportvan / > 206.00 K
......'85 - 4WINNS 160 I.O. / 140hp
.......'74 - Honda CT70 / Real 125
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“I didn’t really say everything I said.”
. . . . . . . . . . . . . . . . . . ~ Yogi Berra ~