OK... I've run into these only and handful of times, but when a regular customer recently moved from one older home into a 1900's home and needed three very large heavy mirrors hung, I did what any smart framer would do.... I consulted with another framer who have more experience than myself. (Rob Markoff sent me some tips and along with my previous experience, I pulled it off!)
I executed this project last month, but wanted to share this with others here and give a thank-you shout out to Rob for his advice and input.
This was the largest of the three mirrors, which also made me the most nervous. As you can see, it came out well. All three mirrors were hung using Hangman (french cleats) 30 inch strips. This largest mirror weights 73 lbs.

I've used Hangman strips before and love them....but never had to rely on them as much as this situation. I prefer these over Z-bar with their traditional lip which grabs regardless of any unevenness to the wall surface. As you can see I used plenty of screws.

Above you can see where I used Rob's painter's tape and envelope trick for collecting any dust while drilling holes on a job. This is perhaps one of my favorite tidbits during 40 years of framing. You will also see that I used Toggler brand wall anchors. Although I normally stock these in my hanging kit, this time I used a style a little different that Rob also suggested... Toggler Alligator wall anchors. These were useful on the first of the three mirrors which was hung into old brick-stone-plaster over a fireplace...

Close-up of Toggler Alligator wall anchor
Continued....
I executed this project last month, but wanted to share this with others here and give a thank-you shout out to Rob for his advice and input.
This was the largest of the three mirrors, which also made me the most nervous. As you can see, it came out well. All three mirrors were hung using Hangman (french cleats) 30 inch strips. This largest mirror weights 73 lbs.

I've used Hangman strips before and love them....but never had to rely on them as much as this situation. I prefer these over Z-bar with their traditional lip which grabs regardless of any unevenness to the wall surface. As you can see I used plenty of screws.

Above you can see where I used Rob's painter's tape and envelope trick for collecting any dust while drilling holes on a job. This is perhaps one of my favorite tidbits during 40 years of framing. You will also see that I used Toggler brand wall anchors. Although I normally stock these in my hanging kit, this time I used a style a little different that Rob also suggested... Toggler Alligator wall anchors. These were useful on the first of the three mirrors which was hung into old brick-stone-plaster over a fireplace...

Close-up of Toggler Alligator wall anchor
Continued....


