Why the Drill Bit Must Match the Wall, Not the Screw

A fixing fails for one of two reasons: the hole was drilled with the wrong bit, or the fixing does not suit the material. Both are decided before the drill touches the wall.

Three materials behave differently

Masonry is hard and brittle. It is drilled by hammering and chipping rather than by cutting, which is why a hammer setting exists on most drills.

Timber is soft and fibrous and is cut cleanly by a sharp spiral bit. Hammer action splits it rather than helping.

Plasterboard is neither. It is a thin brittle sheet with a hollow void behind it, and it has almost no capacity to grip a screw on its own.

The bit does the work the material allows

A masonry bit has a hardened tip designed to withstand impact. Used in wood it tears rather than cuts and leaves a ragged hole.

A wood bit used in masonry blunts within seconds, because the cutting edge is not hard enough for the material and simply wears away.

Metal bits are ground to a different angle again, and using one on a wall produces heat and dust rather than progress.

Plasterboard needs a fixing, not a screw

A screw driven straight into plasterboard holds briefly and then crumbles the board around it, which is why shelves in stud walls sag and then fall.

Cavity fixings work by spreading load behind the board, either by expanding, folding out or gripping a wide area of the rear face.

Each type has a stated load limit, and those limits are modest. Anything heavy should be fixed into the timber studs behind rather than into the board itself.

Finding out what you have

Tapping the wall distinguishes solid from hollow: masonry sounds dead, plasterboard sounds resonant and changes note over a stud.

The dust from a small pilot hole confirms it. Grey or red dust means masonry, white powder means plaster or plasterboard, and shavings mean timber.

Older properties may have lath and plaster rather than plasterboard, which behaves differently again and crumbles readily around any fixing.

Drilling technique follows from the material

Masonry wants steady pressure and a moderate speed, letting the hammer action break the material rather than forcing the bit through it.

Timber wants speed and light pressure, with the bit withdrawn occasionally to clear the flutes so the hole does not pack and burn.

Plasterboard wants no hammer action at all and minimal pressure, because the board offers so little resistance that the bit will punch straight through and damage the surface.