How to hang pictures, mirrors, shelves and TVs on plaster-and-lath walls

Anyone who has lived in a Victorian or Edwardian flat knows the sound. A nail goes in, something behind the paint gives, and a crumb of wall rattles down inside the cavity. That's plaster, and it doesn't behave like the drywall most hanging kits are designed around. Stronger nails won't fix it. Knowing what sits behind the surface, and picking the fastener by what it can reach, will.

#Plaster, lath and what's behind them

A plaster wall is built in layers. Over wood lath the classic method was three coats: a scratch coat and a brown coat about 3/8 inch thick each, then a finish coat of about 1/8 inch, according to the National Park Service's Preservation Brief 21. The wet plaster was pressed through the gaps between narrow wood strips, the lath, and slumped behind them into lumps called keys. Those keys hold the wall on, and a hammer pounding a nail is exactly the kind of shock that cracks them loose.

In San Francisco this is the ordinary wall, not a curiosity. The Park Service notes that plaster was the wall finish for nearly all buildings until the 1930s or 40s, and Census figures put 44.7 percent of the city's housing units as built in 1939 or earlier. One twist matters out in the Sunset and Parkside: by the late 1930s gypsum rock lath had almost entirely replaced wood strips in house plastering, so a house from those years may have plaster over gypsum panels instead.

Not sure what you have? Knock: plaster sounds dense and flat where drywall sounds hollow. Press a pushpin and plaster stops it hard. Check the house's age. And if a magnet sticks almost anywhere on the wall, the lath is metal and the magnet trick below won't help; small test holes will.

#The fastener chooser, by weight

Weigh the piece first: stand on a bathroom scale holding it, then subtract your own weight. Framed glass and old mirrors are always heavier than they look. Then find its line below. The weight lines follow the Earthquake Country Alliance's advice for hanging things where the ground moves.

Up to about 20 pounds: the lath can carry it

• A small frame or a clock, up to about 5 lb. A thin hardened-steel picture hook, the kind with an angled nail, or a 1-1/4-inch screw in a small pilot hole. Either can live in sound plaster alone, though a screw that catches the lath holds better. Put a cross of painter's tape over the spot first. Above a bed or a sofa, add a dot of museum putty at each bottom corner so the frame can't jump its hook in a quake.
• Framed prints or a small mirror, 5 to 20 lb. Drive a screw until it bites a strip of wood lath; you'll feel it grab about an inch in. If it spins in plaster only, back it out and move half an inch up or down to find the next strip. Use two screws for anything wider than your shoulders so it can't pivot. The Earthquake Country Alliance draws its line for hook-and-putty hanging at 20 pounds.

Heavy, pulled on or sticking out: find wood

• A big mirror or heavy art, 20 to 50 lb. This weight goes on a stud. The Alliance's advice for objects up to 50 pounds is to find the nearest stud and screw in a closed-loop hanger, so the wire can't jump off in shaking, with putty or Velcro at the bottom corners. A French cleat screwed across two studs spreads the load and keeps a wide mirror flat. If the piece must sit between studs, a metal snap toggle sized for the full wall thickness is the fallback, but not over a bed.
• Shelves loaded with books or dishes. Count the load, not the shelf. A run of hardcovers or dinner plates sits out in front of the wall and pries at the top screws, which is how hollow-wall anchors work loose. Brackets or a rail system go on studs, with screws long enough to cross about an inch of plaster and lath and still bite deep into the wood.
• A TV on a wall mount. Only on studs, two of them for most mounts. The lag screws have to pass the plaster and lath before they reach wood, so check that the ones in the box are long enough for an old wall. Full-motion arms lever hard on their screws every time the screen swings out. No mount goes on anchors in plaster alone, whatever the package says.
• Over 50 lb: a full-length mirror, an antique, a wall cabinet. Studs, a cleat or the maker's hardware, and a second person. The Alliance suggests considering professional help above 50 pounds, and on old plaster that's sound advice: the work is in proving the studs and drilling cleanly through a wall you can't see into.
• Curtain rods and blinds. Light, but yanked every day, which works screws loose in plaster. Brackets want wood: probe just outside the window casing with a thin bit until you hit framing, and set the brackets there. If you find only plaster, use snap toggles sized for the wall. Curtain and blind installs are a common handyman call for this reason.

Two rules apply to every line. Plaster on wood lath was meant to be at least 3/4 to 7/8 inch thick, the Park Service says, before you count the lath, so read the wall-thickness range on any toggle or molly package; one made for half-inch drywall may never open behind the lath. And hang anything wide from two points. One hook in the middle lets a frame pivot and walk off the wall in a quake.

For a whole gallery's worth of frames, or a mirror you only want to lift once, a picture-hanging pro can find the framing and hang the lot level.

#Finding studs in a plaster wall

Electronic stud finders read density, and plaster is dense everywhere, lumpy in places and backed by lath that runs the whole width of the wall. Some deep-scan models cope; many beep all the way across. These methods work better on old walls, roughly in this order.

1. A strong magnet. Slide a rare-earth magnet slowly across the wall at one height. It snaps to the nails that hold the lath to each stud, and three or four hits stacked in a vertical line mark the stud.
2. Clues in the room. Doors and windows are framed on both sides, so there's wood behind the outer edge of each casing. An outlet or switch box is often fixed to the side of one.
3. Measure, then prove it. From a stud you've found, measure about 16 inches either way, but don't trust the tape; framing in older houses wanders. Prove each stud before anything heavy goes on it.
4. A test hole. Drill a 1/8-inch hole where the piece will cover it. Past the plaster and the lath, the bit either bites solid wood, which is a stud, or drops into air between studs.

#Hanging it without cracking the wall

1. Mark it and tape it

   Pencil the spot, then cover it with an X of painter's tape. The tape holds the finish coat together around the bit so the hole stays clean.

2. Catch the dust first

   In a house built before 1978, mist the spot with water and hold a vacuum nozzle just under it while you drill. The box below explains why.

3. Drill a pilot hole

   Sharp bit, hammer setting off, light steady pressure, low speed. Let the bit cut; leaning on it shatters the edges of the hole.

4. Drive the screw or set the anchor

   By hand or on a low clutch setting. Stop when the screw bites lath or stud; overdriving strips the wood and can crack the plaster around the head.

5. Hang, level, pin the corners

   Hang the piece, level it, then put putty or felt bumpers at the bottom corners. In earthquake country, use a closed-loop hanger so the wire can't jump off the hook.

Most plaster damage traces back to habits that work fine on drywall. Tap each one.

• Heard this?Plaster is too brittle to hang anything heavy.Tap for the factsWhat's trueThe plaster isn't what holds it. A screw through the plaster into a stud carries a heavy mirror without trouble; the skill is reaching the stud without cracking the finish on the way.
• Heard this?A nail is fine if you go gently.Tap for the factsWhat's trueGentle or not, hammering shakes the wall around the nail and can break the keys that hold the plaster to the lath. A pilot hole and a screw do the same job without the shock.
• Heard this?If the stud finder beeps, there's a stud.Tap for the factsWhat's trueOn plaster, many finders beep at lumps, lath and old patches. Confirm with a magnet on the lath nails or a small test hole before anything heavy goes up.
• Heard this?Any anchor from the drywall aisle will do.Tap for the factsWhat's trueMany are sized for half-inch drywall. Old plaster with its lath runs about an inch, so short toggles never open and self-drilling anchors crumble the hole.
• Heard this?Filling a hole in plaster is a big repair.Tap for the factsWhat's trueA screw hole takes a dab of patching plaster or spackle and a touch of paint. Cracks that keep growing and plaster bulging away from the lath are a different matter.

#Picture rail, the Victorian answer

Plenty of Victorian and Edwardian rooms in the city still have a picture rail: a moulding that runs around the room at or a little below the ceiling line. It was there so nobody had to put holes in the plaster. Rail hooks sit over the moulding and the frame hangs on wire or cord at whatever height you like; moving a picture means sliding a hook.

Two cautions. A rail is trim nailed to the framing, not a beam, so keep it to frames and moderate mirrors. And in an earthquake an open rail hook can hop off, so choose hooks that wrap over the moulding and pin the bottom corners of each frame. Where a room has lost its rail, a carpenter can put up a new one screwed into the studs, which suits anyone who reworks a gallery wall often. Trim work like that falls under small carpentry.

#TVs, heavy mirrors and loaded shelves

Anything heavy, anything that sticks out from the wall and anything a child might pull on goes into studs. A TV mount's lag screws have to cross roughly an inch of plaster and lath before they reach wood, so the screws in the box may be too short for an old wall, and full-motion arms multiply the load every time the screen swings out. Then secure the set the way the Consumer Product Safety Commission urges: mounted to the wall, or anchored if it sits on furniture.

San Francisco's emergency office makes the same point for the whole room: its earthquake safety guide tells residents to secure TVs, bookcases, cabinets and mirrors to walls or stable surfaces. Shelves are the job people underestimate. A shelf weighs little; a foot of hardcovers does not, and the load sits out in front of the wall, prying at the top screws. Brackets and any shelf rail system go into studs. Bookcases that stand on the floor are covered in the earthquake guide.

#Renting: holes, deposits and asking first

In a rental the lease comes first; it may say what you can hang and how. California's deposit law, Civil Code 1950.5, allows deductions only for damage that goes past ordinary wear and tear, and it doesn't define where a picture hole stops and damage starts. Picture hooks are the low-risk end. Toggles, TV mounts and shelf brackets are worth an email to the owner first. This is a general summary, not legal advice.

When you move out, a filled hole disappears and a cracked one doesn't. Pull the screws, fill with patching plaster or spackle, wipe it flush with a damp sponge (in a pre-1978 unit, skip dry sanding) and touch up the paint. The move-out guide covers photos, deposits and which marks count as wear and tear. Plaster that bulges, or cracks that keep growing, are another story; the guide to wall cracks helps you read them.