An anchor turns a screw into grip — but only on something that can grip back
Every expanding plug works the same way: the screw pulls a sleeve open and the sleeve presses against the sides of the hole. That mechanism needs sides. In a hollow wall there is nothing to press against; in plasterboard the sleeve simply crushes the gypsum core. So the plug does not fail — it was never in a position to work. Which is why the order has to be: identify the wall, estimate the load, choose the fixing, and only then drill.
The evidence is consistent across every guide written for people who do this professionally: a dedicated plasterboard anchor in 12.5 mm board is rated at roughly 8 kg, and the working advice that follows from it is never to exceed about 5 kg on plasterboard at all. The same anchor in concrete holds an order of magnitude more. Nothing about the anchor changed. The wall did.
Three ways a fixing fails, three different fixes
- Wrong anchor for the wall — a standard plug in plasterboard, hollow block or aerated block. Aerated block is the great deceiver: it drills like soft cheese, the plug feels tight, and then the whole thing pulls out because the material crumbled in a ring around it. The fix is a different fastener, not a tighter screw.
- The hole was oversized, or has already stripped — the plug spins instead of gripping. Once a hole has lost its bite, tightening harder only makes it bigger. Move the fixing, or fill and re-drill, or step up to a purpose-made repair anchor.
- The load was underestimated — right wall, right anchor, too much weight. A metre of hardback books is about 25 kg; a metre of vinyl is around 50. People consistently guess low, then add a safety margin that is far too small.
The two habits that make any anchor stronger
Drill the stated diameter, no wider. A hole 1 mm oversized can halve the grip, and a hole that is too shallow leaves the plug sitting on drill dust instead of seating in the wall. Then clear the dust out — blow it, vacuum it, or work the bit in and out. This is the most skipped step and a very common reason a fixing that felt tight goes soft a week later. After that, one rule for screw length: on a solid wall the screw should enter the plug by at least the plug's full length once it has passed through the bracket. A 25 mm plug holding an 18 mm bracket needs a 45 mm screw, not a 30 mm one. On plasterboard the opposite applies — once the anchor has gripped the back of the board, extra length only risks hitting something in the cavity.
Load direction and the margin
A bracket hanging weight downwards along the wall is doing an easy job — that is shear. Something that gets pulled straight out of the wall is doing a much harder one. A picture is shear; a towel rail that people grab is pull-out, and it needs a far bigger margin. For anything a child might swing on, or that gets knocked, aim for a rated capacity three to four times the expected weight. And when the sum looks uncomfortable on a weak wall, the answer is usually not a bigger anchor but more of them — or a different structure. Four fixing points beat one oversized one, because the limit is the wall's local strength, not the hardware.