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. Still, I was always cautious about hanging things. Because rental apartments in NYC had started out as single-family dwellings and over time became subdivided into apartments you could encounter a real mix of wall substrates, from plaster over masonry to wall board, in the same room. The first step is to determine exactly what your walls are made of, because the methods that work for drywall are the absolute wrong approach for plaster walls and could damage the plaster. Worse, whole shelves could come tumbling down. 

Plaster walls only seem like a pain to work with because new construction has made us accustomed to wallboard. But plaster is wonderful; I love it. Lime plaster gives walls a thickness and luster that is not only visually appealing, it's also healthier (walls can breath and don't get moldy) and more soundproof. Additionally, plaster is far stronger than wallboard and, if you anchor it right, can hold more weight. The most important thing is to use masonry drill bits, so that you don't crumble the plaster. And then there are the different types of fasteners. You want to choose the one that will hold the weight but is the least invasive to your walls.

I've encountered two types of plaster walls. Traditional wood-lath-and-plaster and plaster laid directly over masonry (brick or concrete). As homeowners now, when we gut renovated the bathroom down to the studs I had the opportunity to see and understand how our home had been constructed and what is behind our walls. I took some photos for future reference, and I'm glad that I did. The walls in our 1946 home are plaster over masonry. There is a layer of hard plaster, a bit of space, then concrete blocks. 

Those brown 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 our east wall is an outer wall that has no studs at all, it's just bricks under plaster. This is all good information to know.

After trial and error, here's what I use to hang various things in our home, where almost every wall is filled with art:

Tacks, Home Depot

Light objects
For hanging very light things, such as certain framed photographs, I gently tap in small upholstery tacks. Yup. Tacks work fine for lightweight framed objects, and cause almost no damage. Sometimes I don't even need to fill holes if I change my mind about where I 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 right-size plastic anchor for my object's screws, 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 screws already inserted but I take them out to start. 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.

Crimson Concrete Expansion Anchors

There's another type of wall bolt that expands behind the wall, and I would consider these if I were hanging something really heavy, like a TV, on a concrete wall. Here's an excellent video showing how they work.

Locating studs behind plaster walls

When hanging anything heavy, it's always best to find at least one stud, as no fastener is more fool-proof than screwing directly into a thick piece of wood. Some stud finders will be useless on plaster walls, as 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—and even that's not foolproof. When the thing is beeping at everything, I turn to these tricks for locating a stud from Scott Sidler at The Craftsman blog.

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.