Hairline cracks in plaster — repairs that don't reopen
Most fine cracking is harmless drying or seasonal movement, but it will reopen through a straight filler-and-paint repair every time unless the joint is given somewhere to move.
Tell movement from shrinkage
Shrinkage cracks are fine, stable and often follow board joints or the line of a beam. Structural cracks widen, step through masonry, or open and close noticeably between seasons and need assessing before decoration.
- Straight cracks on board joints: taping failure
- Diagonal cracks from openings: movement
- Map cracking across a wall: surface shrinkage
Open, fill, reinforce
A crack is raked open slightly so the filler has body to grip, dusted out, and filled in layers. Recurring cracks get scrim or a flexible jointing compound rather than a rigid powder filler.
Sanding and priming the repair
Repairs are sanded flush and primed. Fresh filler is far more absorbent than the surrounding paint, so an unprimed repair reads as a dull patch through two finish coats.
When lining paper earns its place
On a wall with widespread map cracking, a heavy lining paper is cheaper and more durable than repeated local repairs and gives a flat, uniform base for the finish.
Common questions
Why do the same cracks keep coming back?
Because a rigid filler in a moving joint simply cracks again. Those joints need a flexible repair or reinforcement.
Should I be worried about hairline cracks?
Usually not — but widening, stepped or diagonal cracks from window corners are worth a structural opinion first.
Does the repair need priming?
Yes. Bare filler is porous and will flash through the topcoat if it isn't primed.
Is lining paper old-fashioned?
It's still the most reliable way to get a flat, uniform surface on a tired wall without a full replaster.
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Next step
Ask for a preparation-first quote — we price the repair work honestly rather than hiding it in the coat count.
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