The best stain block primers, compared.
Top pick: Zinsser Cover Stain 5 litre Best value: Bartoline Stain Blocker Spray – Lowest shelf price in this set, about £6.74 for two 400 ml aerosols, for a small mark. The editorial score is 70. The value badge follows the price. Updated October 2026.
A stain block primer is what you use when a water-soluble mark has already bled through ordinary emulsion. On a UK ceiling that is usually a tide line, nicotine, knot tannin, marker, smoke or grease. It does not repair a live leak, rising damp or soft plasterboard. If the board is soft or the leak is still running, paint is the wrong purchase. The smell is strong, brushes need white spirit, and the data sheet still says to spot-prime knots with shellac first. Zinsser is the 5 litre shellac tin interior odours and knots, with outdoor use limited to spots. How to match the binder to the stain is in the [stain block primer buying guide](/hub/paints-and-varnishes/stain-block-primer/sub/stain-block-primer-buying-guide). A stain block primer stops a water-soluble mark from bleeding into the next coat of emulsion or gloss. Zinsser water-stain guide says moisture should not exceed 12% before.
A stain block primer is what you use when a water-soluble mark has already bled through ordinary emulsion. On a UK ceiling that is usually a tide line, nicotine, knot tannin, marker, smoke or grease.
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How much are you painting?
The 5 litre Cover Stain is the volume tin UK reviewers used on nicotine, smoke, marker, and OSB when several rooms needed the same oil sealer. It is rated 4.7 from only 45 amazon.co.uk reviews, so that star figure sits on a much thinner record than the 1 litre tin at 4.6 from 1,580. At £59.93 it works out at about £12 per litre, lower than the 1 litre Cover Stain at £17.48. The paint-type field only says PAINT, while UK reviews call it an oil-based solvent sealer. One owner described the smell as very strong and lasting a day or two, which rules it out of a room you cannot ventilate. The coverage attribute is only the number 5 with no unit, so this page does not state a spreading rate. The 9.8 m² per litre figure belongs to the 1 litre listing and the data sheet, not to this field. Country of origin is listed as the United Kingdom, and a single small patch does not need this much tin.
Pros
Cons
Best for: Several rooms of smoke or marker staining when you already know you want oil-based Cover Stain.
Less suitable: A single small patch, or a room you cannot ventilate for a day or two.
Specifications
Common questions
Is the 5 litre tin water-based?
The attribute says PAINT, not water-based. UK reviews call it an oil-based, solvent sealer with a strong smell.
How much does 5 litres cover?
The listing coverage field is only the number 5, with no unit, so the spreading rate is not stated on this page.
Does it block nicotine?
One UK reviewer said it covered tobacco staining that ordinary paint had not held. That is an owner report, not a lab test.
Across 1,580 amazon.co.uk reviews, this 1 litre oil primer is the tin UK owners use when a ceiling stain or a wardrobe knot has already come through ordinary emulsion. The listing states 9.8 m² per litre, 0.5 hours touch dry, and a 2 hour full-cure attribute, though one UK reviewer left it much longer before emulsion. Reviewers mention ceiling stains, knots, and a garage door primed under gloss. The recurring complaint is smell: UK reviews call it strong and long-lasting, and brushes need white spirit. The surface line says wood, the bullets say interior and exterior, and an attribute says indoor, so the page is not one clear specification. The listing finish says gloss, which does not match the data-sheet sheen of 12% to 13% at 60°. At £17.48 it has the largest review record in this set and rank 23 in Primer, which is why it is the top pick here, not because a laboratory tested it. Knots remain a limit, because the Cover Stain data sheet says to spot-prime them with shellac first.
Pros
Cons
Best for: A dry interior stain or an exterior wood prime when you can ventilate and clean brushes with white spirit.
Less suitable: A closed bedroom, or a knot that the Cover Stain data sheet says should be spot-primed with shellac first.
Specifications
Common questions
Is this Cover Stain water-based?
The listing paint type is oil. UK reviews describe a solvent smell and white spirit for the brushes.
Can you use it on wood?
The surface recommendation is wood. UK reviews mention wardrobe knots and a garage door under gloss.
How fast does it dry?
The attribute says 0.5 hours touch dry and 2 hours full cure. One UK reviewer left it much longer before emulsion.
This 5 litre shellac primer is the tin the bullets describe for odours, knots, smoke, and varnished wood, with 12.5 m² per litre and a 0.25 hour touch-dry time. At £96.95 it is the highest shelf price in this set, about £19 per litre, and it is rated 4.6 from 85 amazon.co.uk reviews. One UK reviewer used it on a pine ceiling to seal knots, which matches the claim on knots and sap streaks. UK reviews also describe a thin film, and one report mentioned yellowing, so a single coat may not hide a dark mark. The paint-type attribute says enamel while the bullets say shellac, and the waterproof attributes contradict each other, so those ticks are not measurements. The title limits outdoor use to spot priming, so an indoor-and-outdoor tick is not permission to prime a whole exterior wall. Clean-up is not stated on the amazon listing; the manufacturer page specifies denatured alcohol or an ammonia solution.
Pros
Cons
Best for: Interior smoke, pet odour, or knotty wood when you can use a 5 litre shellac tin and work quickly.
Less suitable: A full exterior wall. The title limits outdoor use to spot priming.
Specifications
Common questions
Is B-I-N water-based?
The bullets call it a shellac-based primer-sealer. The paint-type attribute says enamel. It is not described as water-based.
Will it seal knots?
The bullets say it seals knots and sap streaks. One UK reviewer used it on a pine ceiling for that reason.
Can you use the whole tin outside?
The title says interior and spot exterior. The attribute table ticks indoor and outdoor. Do not treat that tick as a full exterior system.
At £15.32 for 750 ml, this white matt tin is the one UK reviewers used on modest ceiling water stains and some coving, and the listing states 8 m² per tin. It is rated 4.4 from 341 amazon.co.uk reviews, a useful count for a small tin, though not the largest in this set. Heavy marks needed several coats before the brown stayed hidden, so one coat is a hope rather than a result. One owner noticed a smell until the film dried, but smell is not the main complaint the way it is with the oil primer. The attribute block lists water, oil, and solvent together, so you cannot read a single binder off the page. An asphalt surface line is not a usable specification for a ceiling. The page asks whether you can use it on a ceiling and whether it needs a separate primer, and it answers neither; owners used this tin on the stain, then emulsion once the mark was opaque. It suits a dry patch when you want less volume than a 5 litre can.
Pros
Cons
Best for: A modest dry water stain on a ceiling when you want a 750 ml tin rather than a 5 litre can.
Less suitable: Anyone who needs a clear oil or shellac specification. The attribute block lists water, oil, and solvent together.
Specifications
Common questions
Can you use this on a ceiling?
The listing asks the question and does not answer it. UK reviews describe water stains on ceilings and coving.
Does it need a separate primer?
The page asks. The file does not say. Owners used this tin itself on the stain, then emulsion once the mark was opaque.
Is it waterproof?
The page asks. The listing does not state a waterproof rating.
Polar Damp Seal is a 2.5 litre water-based internal paint at £38.99, rated 4.4 from 102 amazon.co.uk reviews, sold both as a damp seal and as a stain block. The bullets claim it is solvent free and low odour, cover up to 12 m² per litre, and work as a primer or a topcoat, and they list grease, smoke, nicotine, pen, water marks, crayon, and rust. Some UK owners still reported a smell, low for some and strong or lingering for others, so the solvent-free line is a claim rather than a guarantee of no odour. Touch-dry times conflict: the bullets say 1 to 2 hours and a second coat after 6 hours, while the attribute says 4 hours and a 24 hour full cure. Owners say it is too soon to judge damp results, and some reviews in the file are not about this tin, so the count should not be read as 102 damp tests. The indoor attribute rules out exterior walls, and it does not seal knots the way shellac does. It will not replace a plumber on a live leak.
Pros
Cons
Best for: An internal wall that is clean and dry enough to paint, where you want a water-based damp-seal claim rather than shellac.
Less suitable: Exterior walls, a live leak, or a knot-sealing job. The attribute says indoor.
Specifications
Common questions
Can you use this on exterior walls?
The indoor/outdoor attribute says indoor. The listing does not describe it as an exterior wall paint.
Is it solvent free?
The bullets say water-based, low odour, and solvent free. Some UK reviewers still reported a smell.
How long before a second coat?
The bullets say a second coat after 6 hours and up to 12 m² per litre. The dry-time attribute says 4 hours and full cure 24 hours.
At £6.74 for two 400 ml aerosols, this is the lowest shelf price in the set and the best value pick for a small grease or damp mark you can spray, not for a whole ceiling. It is rated 4.4 from 91 amazon.co.uk reviews and sits at rank 5 in Stain. UK reviews mention oil and damp marks, and one owner said a coat dried in about 15 to 20 minutes. The binder is not named and there is no coverage figure, so you cannot plan a ceiling from the page. One can dribbled at the nozzle and one arrived opened, which is why the editorial score sits below the star rating. The bullets list mould stains, grease, water, rust, smoke, and pen marks on interior walls, ceilings, sills, plaster, and woodwork, but a stain film is not a damp repair. B&Q directions for the same spray say 15 to 25 cm, two or three thin coats, and 15 to 25°C. The manufacturer field says Tetrosyl Limited, which is a listing oddity rather than a second product.
Pros
Cons
Best for: A small grease or damp mark you can spray in a ventilated room.
Less suitable: A whole ceiling or anyone who needs a stated spreading rate and a named binder.
Specifications
Common questions
Is this a spray?
Yes. The listing is two 400 ml aerosols, model PP8155.
Does it block mould?
The bullets say it blocks mould and mildew stains. The file has no test method, and a stain film is not a damp repair.
Can you use it on woodwork?
Woodwork is in the surface list. The file does not state a coverage rate.
We compared six amazon.co.uk stain block primer listings kept for this set. Shelf prices, stars and review counts are the UK listing lines in this batch. Each score is an editorial figure from 0 to 100: stars, then a damper when the review count is thin, then cuts for listing conflicts and faults in UK reviews. The best value badge follows the lowest shelf price for a small job, not the highest score. There was no laboratory test. A higher score ranks a tin inside this set for a stated stain.
Amazon stars
40%The largest share of the editorial score. The figure is the amazon.co.uk star line for that ASIN, not a star rating from another marketplace.
Review volume
30%A thin count pulls the score down. The 5 litre Cover Stain is 4.7 from 45 reviews, against 4.6 from 1,580 on the 1 litre tin.
Listing clarity
30%Cuts for clashes on the same page, such as indoor against exterior, mixed binder lines, a coverage field with no unit, or contradictory dry times, and for faults UK reviews actually describe.
Buy the binder that matches the stain, then the volume that matches the area. A star rating does not tell you whether the tin is shellac, oil or water-based. Nothing in this set repairs a live leak, rising damp or soft plasterboard. Prices are the amazon.co.uk shelf figures in this batch, in GBP.
A stain block primer stops a water-soluble mark from bleeding into the next coat of emulsion or gloss. The marks UK shoppers meet are a ceiling tide line, nicotine, knot tannin, marker, some smoke and grease. Ordinary emulsion has usually failed already. The tin does not repair a live leak, rising damp or soft plasterboard. If the board is soft or the leak is still running, do not buy paint yet. Zinsser UK’s water-stain guide says moisture should not exceed 12% before B-I-N.
If emulsion has already let the mark through, another coat of the same paint repeats the failure. The blocking coat has to match the stain: shellac for knots and odours indoors, oil Cover Stain when you also need a wider prime and can ventilate, water-based when the room is poorly aired and the stain is not a heavy knot.
A household with one dry ceiling tide mark should coat the whole ceiling so the patch does not flash. A 750 ml or 1 litre tin is the usual size for that job. The 5 litre tins are for several rooms, not for a single ring.
None of these listings repairs a live leak, rising damp or soft plasterboard. Cover Stain on a knot without a shellac spot goes against the Cover Stain data sheet. Shutting the windows on an oil primer leaves you with the strong smell UK reviews describe.
Shellac is Zinsser B-I-N: interior odours, knots and a fast recoat, with exterior use limited to spots. The listing is 5 litres at about £96.95, 12.5 m² per litre, 0.25 hours touch dry, 4.6 from 85 reviews. Oil or alkyd is Cover Stain, for interior and exterior surfaces when the listing actually says so, with white-spirit clean-up. The 1 litre tin states 9.8 m² per litre. Water-based, Johnstone’s and Polar’s solvent-free claim, is for poor ventilation and a stain that is not a heavy knot.
Buy the volume for the area. Johnstone’s states 8 m² per 750 ml tin. Cover Stain states 9.8 m² per litre on the 1 litre listing. B-I-N states 12.5 m² per litre. Polar states up to 12 m² per litre. The Bartoline pack does not state coverage. The 5 litre Cover Stain coverage field is unusable. Heavy marks often need a second coat. Plan the solvent. Cover Stain reviewers describe a strong smell and white spirit.
Three typical situations, each with a recommendation from this comparison.
Ordinary emulsion has already let a tide mark through, the board is hard and dry, and you can ventilate. Zinsser Cover Stain, 1 litre, is about £17.48, with 4.6 from 1,580 reviews. The smell is strong and brushes need white spirit.
You already want oil-based Cover Stain across more than one room, and you can leave windows open. The 5 litre tin is about £59.93, about £12 per litre, with 4.7 from 45 reviews. A single patch does not need this much.
You want a water-based claim rather than shellac or alkyd, and you will still open the windows. Polar Damp Seal is 2.5 litres at about £38.99, rated 4.4 from 102 reviews. It is indoor only, and it will not fix a live leak.
The top pick is Zinsser Cover Stain, 1 litre, at about £17.48. It has the largest review record in this set, 4.6 from 1,580 amazon.co.uk reviews, and rank 23 in Primer. The editorial score is 84, cut for a lasting solvent smell and a listing that says indoor in one place and interior and exterior in another. The best value is a different product: Bartoline Stain Blocker Spray at about £6.74, the lowest shelf price, for a small mark you can spray. Its editorial score is 70. The value badge follows that price, not the score. Neither figure is a laboratory test.
Bartoline Stain Blocker Spray
Lowest shelf price in this set, about £6.74 for two 400 ml aerosols, for a small mark. The editorial score is 70. The value badge follows the price.
Editorial
Peter F. is the editor for DIY & tools at productscompared.co.uk. Comparisons in this category are checked against amazon.co.uk listings, review evidence and public UK sources.
Guides on what to look for, how to use a product, and common mistakes.
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.
This page contains affiliate links to amazon.co.uk with the tag pcuk26-21. If you buy through them, we may earn a commission at no extra cost to you. Prices, stars and review counts are the amazon.co.uk listing lines in this batch. We did not run a laboratory test.
