Picture hooks and wall anchors: what each one actually holds, and in which wall

A wall fixing has two numbers: the one printed on the packet, and the one you should design around. The printed number comes from a straight downward pull on a sheet of new, dry, perfectly supported plasterboard in a laboratory. Your wall is none of those things, and the load on a shelf does not pull downwards, it pulls outwards. Nearly every fixing that fails was the right fixing used at its rated limit, in the wrong direction. Here is what each type actually does, which wall it belongs in, and how much of the rated figure to believe.

Identify the wall first, because it decides everything

Knock on it with a knuckle. A dull, solid, unresonant sound is masonry, or plaster over masonry, and almost anything will hold in it. A hollow drummy sound is a cavity wall lining, which in most housing built since the 1960s means plasterboard about twelve millimetres thick with nothing behind it but air.

If it is hollow, find the timber studs before you choose a fixing. They usually sit at four hundred or six hundred millimetre centres, and the cheapest magnetic stud detector finds them by locating the screws that hold the board on. A screw into a stud makes the whole question of anchors disappear.

Older houses have a third wall type: lath and plaster, which is thin timber strips with plaster pushed through the gaps. It sounds hollow, it is brittle, and the rule is to drill rather than hammer anything into it. A hammered pin cracks the plaster key and a palm sized piece comes away from the back where you cannot see it.

Hooks and pins, which are for plaster and for light things

A traditional picture hook with one or two hardened steel pins is a good fixing in plaster over masonry. The pins are hard enough to go through plaster without bending, the hook holds the load against the wall, and the holes are tiny. In solid plaster these will carry several kilograms happily.

In plasterboard alone, the same hook is poor. The pins grip nothing but the soft gypsum core, and the failure mode is slow: the pin tears a slot downwards over weeks and the picture ends up crooked before it ends up on the floor. Hook packets rarely distinguish between the two walls.

This is the right fixing for genuinely light pieces, which covers most cut sheet metal. Something under about a kilogram, such as a cut iron moth, is a single hook problem in plaster and a single self drilling anchor problem in board. The mistake is carrying that assumption up to heavier work.

Hollow wall anchors, in order of what they hold

Plastic expansion plugs, the common ribbed ones, are for solid walls. In plasterboard they spin in the hole and pull straight out. Using one in board is the single most common fixing error there is.

Self drilling screw in anchors, the big threaded cones you drive with a screwdriver, are quick and need no drill. The nylon ones are adequate for a few kilograms. The zinc alloy ones are noticeably better for the same money and are the sensible default for ordinary framed pieces.

Cavity anchors with a collapsing metal sleeve, usually called molly bolts, grip both faces of the board and take more load than any screw in anchor. They also leave a reusable threaded hole, so the screw can come out and go back without destroying the fixing.

Spring toggles and strap toggles are the strongest thing you can put in a hollow wall. Both work by getting a steel bar behind the board, so the load is spread across a wide area rather than concentrated at a hole. For anything heavy, and for anything you cannot afford to have come down, this is the answer. A strap toggle needs a larger hole than you expect, so measure and commit.

Solid walls, where the hole matters more than the plug

In brick, block or concrete, a plug is only as good as its hole. Drill with the correct size masonry bit, on hammer setting, to a depth slightly greater than the plug. A hole one millimetre oversize, which is what you get from a worn bit or a wandering drill, lets the plug rotate and the fixing holds a fraction of what it should.

Blow or vacuum the dust out before the plug goes in. Brick dust in the hole acts as a lubricant and is the reason a plug that felt tight when you pushed it in spins when you drive the screw.

Avoid the mortar joints if you can, and go into the brick itself. Mortar in older houses can be lime based and soft, and a plug in a crumbling joint has nothing to expand against. If the drill suddenly gets easy, you have found an old soft joint or a void in a block, and the fixing needs to move.

The rated weight, and how much of it to use

Divide the printed figure by three or four. Manufacturers quote a static pull out figure, measured once, on fresh board, in the laboratory's preferred direction. Real walls have been drilled before, real board has been damp at some point, and real loads get leaned on, knocked and loaded unevenly.

Then think about direction, which matters more than the number. A picture hanging flat against a wall loads the fixing mostly downwards, in shear, which is the direction plasterboard copes with best. A shelf loads it outwards: the weight sits away from the wall, the shelf tries to rotate, and the top fixing is pulled straight out of the board. That is the weak direction and it is where anchors fail.

So a shelf is a different problem from a picture of the same weight, and a deeper shelf is a different problem again. A piece like a coffin shaped wall shelf carries its own weight plus everything that ends up on it, applied as a lever. Into a stud, or into toggles, or not at all.

Two fixings beat one, nearly always

Anything wider than about forty centimetres wants two hanging points rather than one, for three reasons: each fixing carries half the load, the piece cannot swing out of level, and if one fixing does start to move you notice it as a tilt before it becomes a failure.

Use D rings on the back rather than a single wire where you can. A taut wire over one central hook concentrates everything at one point and raises the effective hanging height as the wire stretches, which is why pictures hung on wire creep upwards and then sag to one side. Wire also fails at the twist, not in the middle.

Position two fixings about a quarter to a third of the width in from each edge. Measure the distance between the D rings, transfer it to the wall with a level, and drill both before you hang anything, because adjusting one fixing after the other is in place is how walls acquire extra holes. A rail with several load points, like a coat rail with a hook on every rib, follows the same principle and needs every mounting hole used rather than the two that happen to line up.

Adhesive, and where it genuinely works

Adhesive hanging strips work on smooth, clean, fully cured paint, which usually means at least a couple of weeks after painting and often longer. Clean the wall with isopropyl alcohol rather than a household spray, because the surfactants in cleaning products leave a film that the adhesive cannot grip.

They are rated for a load hanging straight down against the wall. Anything that stands proud, pulls outward or will be knocked is outside what they are designed for. They also do badly on matte emulsion, textured paint and wallpaper, where they either refuse to bond or take the surface with them on removal.

Within those limits they are genuinely useful for light flat pieces, and they are the only no holes option that holds anything at all. Outside them, a single small hole and a smear of filler when you leave is the lower risk choice, and the honest one.

Questions people actually ask

What anchor should I use in plasterboard for a heavy item?

A spring toggle or a strap toggle, which put a steel bar behind the board and spread the load. Better still, find a timber stud and use a fifty millimetre woodscrew, which is stronger than any anchor in the board itself.

How much weight can a plasterboard anchor really hold?

Assume between a third and a quarter of the printed rating. The quoted figure is a single straight downward pull on new board in laboratory conditions, and it does not account for a load that pulls outwards, which is how shelves and anything that stands proud of the wall behave.

Can I use a plastic wall plug in plasterboard?

No. Ribbed plastic expansion plugs are designed to expand against solid masonry. In hollow board they spin in the hole and pull straight out. Use a self drilling anchor, a molly bolt or a toggle instead.

Do I need two hooks or one?

Two for anything wider than about forty centimetres. Each fixing then carries half the load, the piece cannot swing out of level, and a fixing that starts to move shows up as a tilt rather than as a failure.

Is it safe to hammer a picture hook into lath and plaster?

No, drill it. Hammering cracks the plaster key behind the laths, and the damage happens out of sight on the back of the wall. A small pilot hole and the right anchor keeps the plaster intact.