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Saturday, February 27, 2016

Hanging Heavy Things on Masonry-Plaster Walls

I used toggle bolts to hang these floating shelves
Before we became homeowners, we lived in many rentals in New York City. Lucky for me, none of our landlords ever stipulated in the lease that we couldn't hang things on the walls or paint the walls bright colors, the way you hear many landlords do. (Imagine me with my crafty hands bound to my sides with duck tape. LOL.) Still, I was always cautious about hanging things. Over time, I learned all the tricks for hanging things on drywall. Sadly, all those methods are the absolute wrong approach for plaster walls and could damage the plaster or, worse, whole shelves could come tumbling down. I had to start from scratch to learn what works best for plaster.

I shouldn't have worried so much. It turns out that plaster is way stronger than wallboard and can hold more weight. I just need to use masonry drill bits, so that I don't crumble the plaster. And I use different types of fasteners. The key I've found is to use the fastener that will hold the weight but is the least invasive to the walls.

The walls in our 1946 home are plaster over masonry. This means there's a layer of hard plaster, a layer of space, then concrete blocks. When we gut renovated the bathroom down to the studs, it provided a good opportunity for me to see and understand how our home had been constructed and what was behind our walls. I took some photos for future reference, and I'm glad that I did.



Those squares that look like cardboard are actually cement blocks. The holes that look like they have cotton batting tufting out of them, actually have globs of hardened white concrete sticking out. That's what the plaster would adhere to. The wall studs — those vertical wood 2x4s — are generally located every 16" along most of our walls. I say "most' because the east wall has no studs at all, it's brick under plaster. All good information to know.

After trial and error, here's what I use:


Tacks, Home Depot
Light objects
For hanging very light things, such as certain framed photographs, I tap in small upholstery tacks. Yup. Tacks work fine for most light-weight framed objects, and they cause almost no damage. Sometimes you don't even have to fill the holes if you change your mind about where you want to hang something. For slightly weightier light-framed art and for large canvas paintings — which, even though they are large, do not weigh much — I pre-drill tiny pilot holes using a masonry bit, then fasten screws halfway, leaving enough head to hang things.

Plastic Anchors, Home Depot
Medium objects
For hanging heavier art, curtains, and window shades, I use plastic anchors. I pre-drill a pilot hole using a masonry bit, gently hammer in the plastic anchor, then fasten the screw inside the anchor.


Heavy objects
For hanging very heavy objects, such as cabinets, floating shelves or other wall-mounted storage, I try to locate at least one stud — more on that below. For the other holes I use metal molly bolts or toggle bolts. Mollys look sort of like plastic anchors, but they are metal and the cuff has teeth on the underside that dig into the wall.

Molly Bolt
They come with the screws already inserted but I take them out. Not always necessary, but I like to put a drop of quick-set glue in the cuff of the anchor and let it dry to be sure it has firm contact with the wall before I screw in the bolt. This keeps the bolt from spinning in the hollow wall. Not always necessary, but why not. Mollys can hold things up to 50 pounds.

Toggle Bolt, Home Depot

Very heavy objects
For cabinets or wall-mounted shelves that will be holding hundreds of pounds, I use metal toggle bolts. Some call these butterfly bolts, because the wings expand once they are behind the walls. I don't love them because the holes required are fairly large to be able to slip them behind the wall, hold it there, and turn the screw to activate the spring mechanism. The holes don't show once you mount your shelf, but I'm still squeamish about making big holes in my walls.

Locating studs behind plaster walls

Some stud finders are useless on plaster walls, because they can't tell wood lathe from wood stud. I have a stud finder that's pretty sophisticated and can locate wood, deep wood, metal, deep metal, and electrical current — sometimes. When I can't, these tricks for locating a stud from Scott Sidler at The Craftsman blog may help.

1. Find an electrical box
Most electrical boxes for outlets and light switches are located on either side of a stud. Turn off the breaker, take off the face plate, nose around with a screwdriver on either side of the box to see if there is wood.

2. Knock on the wall
Simple is sometimes best. Knock along the wall and listen. Sections without a stud will sound hollow. When you hit a stud you will hear a thunk. Mark the thunks. Are they about 16" apart? You've found your studs.

3. Use a magnet
The reason this works on lathe and plaster walls, according to Scott, is because wood lath is nailed to the studs and the magnet will find the nails. I haven't tried this, because our bathroom reno revealed that we have plaster over masonry not lathe. If you want to try this, tie a piece of dental floss around a common fridge magnet and dangle it against the wall, moving along. When the magnet sticks to the wall, you've found a stud.

4. Use a metal detector
Works on the same premise as the magnet technique, but may get false positives if the device is strong enough to pick up old wiring, cast iron plumbing, or other things behind your walls.

Once you find one stud, you can measure off 16″ or 24″ (standard) along the wall to find the next one. Stick a vertical strip of painter's tape along the wall and mark them.