How do I fix plasterboard where the board edge does not land on a stud?
An unsupported board joint cracks however often it is filled — the answer is a noggin behind it, and the details that make the joint disappear afterwards.
- Difficulty
- intermediate
- Time
- 1 hr
- Read
- 5 min
- Safety
- caution
Short answer
A board edge with nothing behind it lets both boards flex independently, which cracks the joint in a dead straight line every time. Cut in a timber noggin between the studs, centred under the joint so each board gets half of it, screw both boards to it, then tape and fill. Filling without support just reopens the same crack.
This is the fault behind a very large proportion of the recurring straight cracks people fill year after year. It is not a filler problem and no product will solve it, because the joint itself has nothing behind it. Once you know what you are looking at, the repair is straightforward carpentry.
Safety
What you'll need
- timber to suit the stud depth
- drywall screws
- a plasterboard offcut, if replacing a section (optional)
- paper tape or scrim, and jointing compound
- a torch and a stud detector
- a sharp utility knife and a pad saw
Step by step
- Confirm the diagnosis before opening anything up.A dead straight crack, usually vertical, that reappears after every repair and that does not correspond to a structural line. Push on either side of it — if the two sides move independently, the joint is unsupported.
- Find the studs each side and check the void.Detector first, then a small exploratory hole and a torch. You are looking for cables, pipes, and anything else in the way before you commit.
- Open the joint up enough to work.Cut back the failed filler and tape, and where necessary cut a strip of board away on each side of the joint so you can get a noggin in and screw to it.
- Cut a noggin to fit tightly between the studs.Same depth as the studs so it sits flush with the front face. A loose noggin does nothing; it should need a tap to go in.
- Fix the noggin so its centre falls under the joint.Screw through the studs into its ends where you have access, or fix it with angled screws from the front where you do not. Each board then gets roughly half the noggin's width to be screwed to.
- Screw both boards to the noggin at regular centres.Set the heads just below the paper face without breaking the paper. A screw that tears through the paper has no holding power and will show as a pop later.
- Bevel the cut edges of the board slightly.Factory tapered edges sit in a recess so tape and filler finish flush. Cut edges have no taper, so a shallow chamfer along the cut gives the compound somewhere to sit.
- Tape the joint and finish in three progressively wider coats.Bed the tape, then two wider coats feathered well out. On a long joint, wider is always better.
- Prime the repair before decorating.New compound is much more absorbent than the wall and will flash through the paint otherwise.
Tips
- Where a wall is being boarded from new, plan the board layout so every edge lands on a stud and the horizontal joints are staggered between adjacent boards.
- Where a board edge genuinely cannot reach a stud and there is no access for a noggin, proprietary metal backing clips exist for exactly this situation.
- If several joints on the same wall are cracking, the boarding was probably set out badly throughout — consider overboarding the whole wall rather than repairing joint by joint.
- A crack that runs diagonally, or from the corner of a door opening, is not this fault. That is movement, and it needs a different diagnosis.
Common mistakes
- Filling the crack again with a flexible filler — The joint is not a hairline shrinkage crack — it is two independent panels moving relative to each other by a real amount. No filler bridges that indefinitely, which is why the crack has already come back several times.
- Fixing the noggin so one board only just catches its edge — If the noggin is off-centre, one board is screwed close to its edge — which crumbles — and the other may have almost no bearing. Centre it so both boards get a proper share.
- Driving screws through the paper face — Plasterboard's tensile strength is in its paper. A screw that punches through has nothing gripping it, so it works loose, and the head then pushes the filler off as a nail pop.
If it doesn't work
Crack reopens each winter in the same line
Cause: Unsupported board edge — Fix: Open it up, fit a noggin, screw both boards to it, re-tape and finish.
Board flexes when pressed but the studs are where they should be
Cause: Board not screwed to the studs at proper centres — Fix: Add screws at the manufacturer's spacing along every stud, set below the paper face, then fill and finish.
Noggin fitted but the joint still cracks
Cause: Screws missed the noggin, or the noggin is loose in the void — Fix: Check the fixing pattern with a magnet or a detector. A noggin that moves has to be refixed properly at both ends.
Questions people ask
Can I fit a noggin without taking the board off?
Sometimes, by cutting a narrow slot, sliding a longer piece of timber in and screwing through the board into it while holding it with a temporary screw — a technique similar to fitting a batten behind a plasterboard hole patch. It is fiddly and the timber has to end up genuinely tight and fixed.
What size timber should the noggin be?
The same depth as the studs so its face is flush with theirs, and wide enough that each board gets a decent bearing — a noggin only as wide as the joint gives each board a few millimetres, which is not enough to screw into reliably.
Is it worth just overboarding the wall?
If more than one or two joints are failing, yes, and it is often quicker. A fresh layer of board fixed through to the studs, with joints set out to land on studs and staggered from the ones behind, gives a wall with no inherited defects.