Because the paper face is what holds the board, and a small head tears straight through it.

The gypsum core has almost no fastener-holding strength of its own.

A broad, thin head spreads the load over enough paper to resist pull-through.

It also gives a large enough area to be covered smoothly by jointing compound.

A thin head is important as well as a broad one, since a thick head cannot be concealed.

This is the same reasoning as a clout nail, applied to a different material.

A shallow depression left by the hammer, with the head just below the surface and the paper unbroken.

The head has to be below the surface so jointing compound can cover it smoothly.

Breaking the paper destroys the only material holding the fixing, so the nail holds very little afterwards.

A head left proud shows through the finish and catches the trowel.

A convex-faced plasterboard hammer produces the dimple consistently, which is why the tool exists.

The same principle applies to screws, where a depth-limiting nose does the job automatically.

The timber frame drying and shrinking, which leaves the nail standing proud of a board that has moved.

Framing timber loses moisture after the building is closed in and heated.

As it shrinks, the board stays where it is and the nail head emerges through the finish.

Ring-shanked nails resist this far better than plain ones, because they cannot back out easily.

Using drier framing timber and delaying boarding both reduce the problem.

Screws are less prone to popping, which is one of the main reasons they replaced nails.

Screws for most work - they do not pop, they drive to a controlled depth, and they hold better as the frame moves.

Collated screw guns with depth-limiting noses make the dimple automatically and at speed.

Screws also allow a board to be removed and refitted, which nails do not.

Nails remain in use for speed on some ceiling work and where a screw would be slower.

Some traditions specify double nailing patterns that are still followed.

Board and system manufacturers state which fixings maintain their fire and acoustic performance, and that specification governs.

Board thickness plus the penetration into the timber that the board specification calls for - it is a stated figure.

Penetration into the framing is what actually holds the fixing.

Too short and hardly any of the nail is in the framing at all.

Too long is wasteful and can protrude through a thin batten.

Double-layer boarding needs a longer fixing for the outer layer than the inner one.

Fire-rated and acoustic systems specify fixing length and spacing as part of the tested construction.

Galvanised as standard, stainless in humid rooms - a rusting fixing stains through the finish permanently.

Corrosion products bleed a brown mark through jointing compound and paint.

The stain reappears every time the wall is redecorated unless the fixing is removed.

Bathrooms, kitchens and utility rooms are the usual problem areas.

Moisture-resistant board is used in those rooms precisely because damp is expected, so the fixing should match.

Some board systems specify a particular fixing finish as part of the tested construction.

As the board or system manufacturer specifies - spacing is part of the tested construction, not a matter of judgement.

Perimeter spacing is normally closer than in the field of the board.

Ceilings are fixed more closely than walls because the load is constant and downward.

Fire-rated and acoustic systems have their own spacing, and departing from it invalidates the tested performance.

Edge distance matters too, since a fixing too close to a board edge crumbles the core.

Double-layer systems specify different patterns for each layer.