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Stain block primer buying guide

Updated: October 2026

You have already rolled emulsion over a brown ceiling ring, a nicotine patch, or a knot, and the mark has come back through the new paint. A stain block primer buying guide should start with the stain and the room, not with the star rating. This comparison holds six amazon.co.uk listings: a shellac tin, two sizes of oil primer, a small matt stain block, an aerosol, and a water-based damp seal. The [stain block primer comparison](/hub/paints-and-varnishes/stain-block-primer) scores those listings. The Products Compared editorial team used the amazon.co.uk listings on 16 October 2026, with no laboratory test. A qualifying purchase can earn a commission.

You have already rolled emulsion over a brown ceiling ring, a nicotine patch, or a knot, and the mark has come back through the new paint.

Our top picks

Zinsser Zinsser Cover Stain 1 litre

Best overall

Zinsser Zinsser Cover Stain 1 litre
9.4/10about £17.48
View offer
Johnstone's Johnstone's Stain Block 750 ml

Alternative

Johnstone's Johnstone's Stain Block 750 ml
8.6/10about £15.32
View offer
Bartoline Bartoline Stain Blocker Spray

Best value

Bartoline Bartoline Stain Blocker Spray
8.0/10about £6.74
View offer
On this page
  1. 1.Name the stain before the brand
  2. 2.Shellac, oil, water-based, aerosol
  3. 3.Coverage and tin size
  4. 4.Smell, clean-up, and the VOC cap

Name the stain before the brand

A water tide mark, cigarette staining, a resinous knot, and a grease spot do not ask for the same film. Water-soluble colour in a dry ceiling will bleed into the next coat of emulsion unless something stops it dissolving again. Smoke and pet odour need a sealer that also claims to lock smell. In this set that claim sits on the shellac tin. If you cannot name the stain, do not open with the largest tin. A 750 ml or 1 litre tin lets you see whether the mark stays hidden before you commit to 5 litres. A live leak, soft plasterboard, or a ceiling that is still cool and damp is not a binder decision at all. Zinsser UK’s water-stain guide says moisture should not exceed 12% before B-I-N, and Checkatrade’s leak advice is not to paint damp board.

Shellac, oil, water-based, aerosol

Zinsser B-I-N, 5 litres at £96.95, is shellac. The UK product page gives about 15 minutes touch dry, about 45 minutes to recoat, and 12.5 m² per litre, and it limits outdoor use to spot priming. Zinsser Cover Stain is the oil primer, at £17.48 for 1 litre and £59.93 for 5 litres. Johnstone's Stain Block, 750 ml at £15.32, is the small white matt tin. The listing states 8 m² per tin, but the attributes list water, oil, and solvent together. Bartoline’s two 400 ml aerosols at £6.74 are for a spot you can spray, not for a ceiling. Polar Damp Seal, 2.5 litres at £38.99, is a water-based internal damp-seal paint that also lists stains. Which listing to open first is on the best stain blocking paint page.
Zinsser Zinsser Cover Stain 1 litre

Testsieger

Zinsser Zinsser Cover Stain 1 litre
9.4/10about £17.48
View offer

Coverage and tin size

Coverage is the figure that stops you buying a sample tin for a whole ceiling, or a 5 litre can for a dinner-plate ring. Johnstone's states 8 m² per 750 ml tin. Cover Stain states 9.8 m² per litre on the 1 litre listing and on the data sheet. The 5 litre Cover Stain page only shows the number 5 with no unit, so do not use that field as a spreading rate. B-I-N states 12.5 m² per litre. Heavy marks often need a second coat, which cuts the practical area.

Smell, clean-up, and the VOC cap

Cover Stain reviews describe a strong smell that can last. Brushes from that tin need white spirit. B-I-N is not a water clean-up either. The manufacturer page specifies denatured alcohol or an ammonia solution, and the room still wants fresh air while you work. The Volatile Organic Compounds in Paints, Varnishes and Vehicle Refinishing Products Regulations 2012 (SI 2012/1715) cap a solvent-borne primer at 350 g/l of ready-to-use product and a water-borne primer at 30 g/l. Cover Stain’s sheet sits at 335 g/l, under that solvent cap. Once you have chosen a binder, the coat order is in how to use stain block primer. The Zinsser pair on its own is in Zinsser B-I-N vs Cover Stain.

Common questions

Do I need shellac, oil, or a water-based tin?
Use shellac (B-I-N, £96.95 for 5 litres) for interior odour and knots, with outdoor work limited to spots. Use oil Cover Stain when you need a full interior or exterior prime and can ventilate. Use Johnstone's at £15.32 or Polar at £38.99 for a modest dry mark in a room you do not want full of solvent. If the stain is unclear, buy the smaller tin first.
Is an aerosol enough for a ceiling?
No. Bartoline is two 400 ml cans at £6.74 and states no coverage. B&Q’s directions are 15 to 25 cm and two or three thin coats, which suits a sill or a grease spot. A ceiling ring needs a brush or roller tin with a stated spreading rate, then a topcoat over the whole plane.
What does 8 m² per tin mean for a patch?
Johnstone's 8 m² figure is one coat at the stated rate, not the size of the brown ring. A plate-sized mark uses little of the 750 ml tin, and a second coat uses more. Finish the whole ceiling so the patch does not flash. If the stained area plus a second coat would pass 8 m², look at Cover Stain at 9.8 m² per litre.
Why do Johnstone's attributes list water, oil, and solvent?
Those three words appear together in the attribute block, so none of them is a clean specification. The paint-type line leans water-based, but it is not a data sheet like B-I-N or Cover Stain. The asphalt line is a bad attribute, not a driveway instruction. If you need a named binder, buy the tin whose sheet states it.
Can I use B-I-N on the whole outside of the house?
No. Zinsser limits outdoor B-I-N to spot priming, and the 5 litre title says interior and spot exterior. An indoor-and-outdoor tick does not make a full exterior system. Cover Stain is the oil primer sold for interior and exterior surfaces, though its 1 litre attribute also says indoor. Knots still want a shellac spot first.
When is 5 litres better value than 1 litre?
When you already want Cover Stain for more than one room. Five litres is £59.93, about £12 per litre, against £17.48 for 1 litre. The 4.7 rating rests on 45 reviews, against 4.6 from 1,580 on the small tin. One ceiling patch does not need 5 litres, and an unventilated room should not take the oil tin at either size.

Related pages

Paint over water stains on a ceiling

Stain block primer

Best stain blocking paint UK: top pick, best value

Zinsser B-I-N vs Cover Stain: shellac or oil prime

How to use stain block primer once the board is dry

Sources

Public UK sources for the primer rules, ventilation and manufacturer figures on this page. Prices, stars and review counts are the amazon.co.uk listing lines in this batch.

  1. SI 2012/1715 — VOC in paints and varnishes (retrieved 17 October 2026)
  2. HSE INDG273 — Solvents and ventilation (retrieved 17 October 2026)
  3. Zinsser UK — B-I-N (retrieved 17 October 2026)
  4. Zinsser UK — Cover Stain (retrieved 17 October 2026)
  5. Zinsser UK — Water-stained surfaces (retrieved 17 October 2026)
  6. Checkatrade — Water leaking from a ceiling (retrieved 17 October 2026)
  7. Johnstone’s 750 ml retailer notes (retrieved 17 October 2026)
  8. B&Q — Bartoline stain blocker spray directions (retrieved 17 October 2026)