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Filler for hairline cracks

Updated: October 2026

A pale line of about 2 mm to 3 mm shows when the light rakes the wall, and a heavy tub will sit on it instead of going in. Filler for hairline cracks has to be a fine paste, pressed across the line and feathered flat. The [indoor wall filler comparison](/hub/fillers-adhesives-and-sprays/wall-filler-indoor) holds the captured packs and their GBP prices. Prep and the lid are on [how to fill cracks in walls](/hub/fillers-adhesives-and-sprays/wall-filler-indoor/sub/wall-filler-indoor-how-to-fill). This page stays with the fine crack. Prices were written up on 16 October 2026. This is not a lab test. A qualifying purchase can earn us a commission at no extra cost to you.

A pale line of about 2 mm to 3 mm shows when the light rakes the wall, and a heavy tub will sit on it instead of going in. Filler for hairline cracks has to be a fine paste, pressed across the line and feathered flat.

Our top picks

Polycell Polycell Multi-Purpose Polyfilla 330 g

Best overall

Polycell Polycell Multi-Purpose Polyfilla 330 g
9.3/10about £3.49
View offer
Palace Palace Fine Surface Filler 600 g

Best value

Palace Palace Fine Surface Filler 600 g
8.5/10about £1.25
View offer
Palace Palace Langlow filler 1 kg

Alternative

Palace Palace Langlow filler 1 kg
9.2/10about £6.99
View offer
On this page
  1. 1.Two millimetres and three millimetres
  2. 2.Feather the edge
  3. 3.The tub in this set
  4. 4.When it is not a hairline

Two millimetres and three millimetres

Polycell Fine Surface is for indoors, on wood and plaster, for cracks up to 2 mm, with a recoat in about 60 minutes. That tube was not in the twelve listings. Palace Fine Surface is layers no more than 3 mm, skinning in about 30 minutes and curing in up to 24 hours. The amazon.co.uk listing is worded for interior surfaces, so treat that tub as indoor. It is not rated to 2 mm. Do not borrow a 5 mm limit from another brand.

Feather the edge

Open a closed hairline slightly, a couple of millimetres, so the paste can key. You are not cutting a deep V. Brush the dust out and keep the crack dry if you follow Polycell's fine-surface how-to, which also wants oil-based paint on nail heads. Press the fine paste across the crack, then draw it out onto the sound paint. A feather edge thins to nothing. Sand flush if the product asks. Palace's sheet says the paste can be sanded. Then paint. One coat over bare white paste can leave a lighter island. Mesh and plug compound do not belong on a line you can barely fit a knife into.
Polycell Polycell Multi-Purpose Polyfilla 330 g

Testsieger

Polycell Polycell Multi-Purpose Polyfilla 330 g
9.3/10about £3.49
View offer

The tub in this set

The fine tub that was captured is Palace Fine Surface, 600 g, at about £1.25, rated 4.6 from 2,247 reviews, with layers no more than 3 mm. A 120 ml volume line conflicts with 600 g, so buy the 600 g tub. It is the best value fine filler here, and the top pick on this page only for that shallow job. One person used it on big holes and decided that was wrong. Lids in the reviews split or fail to seal, so press the cover flat. Polycell Fine Surface stays the 2 mm specification, without a captured price.

When it is not a hairline

A crack that opens and closes with the heating is not a line you can lock with rigid fine paste. Flexible Gap is quoted at up to 5 mm wide and 12 mm deep, and it was not in the twelve listings. A separate mention of 20 mm is not the limit used here. A finger hole needs mesh and a deeper paste. Do not hide a 2 mm line with plug compound, scrim, or brick-effect tiles.

Common questions

What counts as a hairline crack here?
A fine crack of about 2 mm to 3 mm that you see in raking light. Polycell Fine Surface is published up to 2 mm. The Palace tub here is layers of 3 mm. A finger hole, a screw hole you must build up, or a skirting gap that moves is a different job.
Is 2 mm the same limit as 3 mm?
No. Polycell Fine Surface is the 2 mm indoors specification, and that tube was not captured. Palace Fine Surface is layers no more than 3 mm. A 5 mm filler from another brand is a third spec. Use the number on the tub you are holding. Do not stretch Palace to 5 mm.
Should I open the crack before I fill it?
Yes, slightly, so the paste can key. A closed hairline is easy to bridge, and the line then returns through the paint. Open it a couple of millimetres, brush the dust out, and keep it dry on the Polycell fine-surface how-to. You are not cutting a deep channel.
What is a feather edge?
A fill that thins to nothing, with no ridge. Press the paste across the crack, draw it out, and sand flush once it is firm if the product allows it. Palace's sheet includes sanding. Polycell Fine Surface says sand if needed. If your fingers find a step, the emulsion will too.
Can I use multi-purpose filler on a hairline?
A heavier paste often bridges a 2 mm line instead of entering it. Fine filler, at its own limit, is the paste for that crack. Keep multi-purpose paste for a screw hole inside that tub's depth. If a ridge of heavy filler is already there, sand it back and refill.
Is the £1.25 tub the fine filler in this set?
Yes. Palace Fine Surface at about £1.25, 600 g, rated 4.6 from 2,247 reviews, is the captured fine tub. It is the best value for a shallow interior crack here, and the top pick only inside 3 mm layers. Polycell Fine Surface at 2 mm was not in the twelve. Some lids split, and the paste then goes hard.
Will the crack come back if the joint moves?
Yes, if the skirting or frame moves. A rigid fine filler cracks again. Flexible Gap, quoted at up to 5 mm wide and 12 mm deep, is the other job, and it was not in this set. If a stain keeps returning, or plaster is loose over a wide area, stop.

Related pages

Indoor wall filler buying guide

Best indoor wall filler

Indoor wall filler

Fill a deep hole in plasterboard: depth, mesh, screws

How to fill cracks in walls: layer, sand, and paint

Sources

Public UK sources used for this comparison. Listing prices are the GBP figures captured for these amazon.co.uk ASINs and were not re-checked on 16 October 2026.

  1. Polycell Multi Purpose Polyfilla Ready Mixed (retrieved 15 October 2026)
  2. Polycell Fine Surface Polyfilla (retrieved 15 October 2026)
  3. Polycell Deep Gap Polyfilla (retrieved 15 October 2026)
  4. Polycell Advanced Polyfilla (retrieved 15 October 2026)
  5. Polycell Flexible Gap Polyfilla (retrieved 15 October 2026)
  6. Polycell — fill awkward or large gaps (retrieved 15 October 2026)
  7. HSE — Construction dust (retrieved 15 October 2026)
  8. HSE CIS36 — Construction dust (retrieved 15 October 2026)