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Stain Blocking Primer

Product Information

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It’s easy to keep your paint job looking great by applying a base coat of stain blocking primer first, stopping tannins from wood coming through and staining your paint coating.

Thorndown Stain Blocking Primer is a high performing wood surface primer primarily developed for tannin and stain blocking on timber surfaces.

It works on all untreated softwood and hardwood timber surfaces, including pine, cedar, redwood, plywood, MDF and hardboard. And pressure treated timber, Accoya, and all painted surfaces of timber, masonry and plaster.

  • Works on all untreated softwood and hardwood timber surfaces, including pine, cedar, redwood, plywood, MDF and hardboard. On oily hardwoods such as Iroko drying time will be greater
  • Works on pressure-treated timber and Accoya
  • Works on all painted surfaces of timber, masonry and plaster
  • Quick drying – Dry in 1 hour in fine weather cnly 1 coat is needed but you can apply a second on particularly resinous or troublesome wood, like very knotty woods or ones with high tannin bleed or leeching
  • Water-based primer, sealer and stain killer
  • Suitable for use on interior and exterior surfaces
  • Excellent adhesion to all timber and painted surfaces
  • Blocks stubborn and persistent stains including water stains, marker pens and more
  • Seals porous surfaces with excellent blocking of bleeding knots and sap streaks
  • Flash rust inhibitor prevents rust forming while drying
  • Fungicide film preservation stops the paint film degrading with mould
  • Low VOC
  • Coverage up to 12m2 per litre on smooth surfaces, 6m2 on rough surfaces
  • Moisture regulating microporous primer
  • Water wash up
  • Apply with brush (high quality synthetic recommended), roller or sprayer
  • Available in Clear, White, Grey and Black

You can view and download a pdf of Stain Blocking Primer USPs here, or download the full Stain Blocking Primer USP and Application Advice sheet.

Application Guide


Brush, roller (small or medium nap ‘hairy’ roller rather than foam), or sprayer; also sandpaper, and wood preserver if required.


Make sure all surfaces are clean, dry and sound. For best results, sand surfaces and use a wood preservative if needed on untreated fresh timber.


Shake tin and stir thoroughly before use and stir when required during application.


Use a brush, roller, or sprayer.

‘Avoid the rain, and apply with the grain’, as they say, and leave to dry.

When coating large areas, paint up to still-wet paint, as applying over dry paint can make things look uneven.

Use on light paint colours to block tannin stains from coming through, and on resinous knotty wood to block resin and sap bleed.


This stain-blocking primer is designed to block resin bleed and tannin stains from discolouring paint coatings. Apply before paint top coats. Adheres well to wood, masonry, stone, concrete, terracotta and plaster.

One coat should do the trick, but you can apply a second on particularly resinous or troublesome wood, like very knotty woods or ones with high tannin bleed or leeching.


In fine weather, a single coat dries easily in an hour or two (20oC and low humidity), ready to paint on a second coat if required, or to apply a paint top coat.

Drying times are extended in cooler weather so as a rule of thumb, double the recommended drying time if  temperatures a lot colder than 20oC.


Use hot or cold water, with or without detergent, on paint-wet equipment.

Be very careful not to allow sprayer nozzles to dry out – this will make cleaning them almost impossible!


Paint will keep for approximately 2 years or more in a sealed tin stored out of freezing or extremely high temperatures. Just mix well before use as the paint will have separated a lot over the years. Using a cheap hand blender does the job very well and with no effort! 


Please, please don’t throw away unused or dried paint or preserver into drains or watercourses. Most local authorities have free facilities for disposing of paint and coatings.

All of the packaging we use is fully recyclable.

  • Box – made from FSC cardboard and fully recyclable
  • Internal packaging – loose starch fill is biodegradable and compostable. Moulded tin protectors are made from recycled cardboard and are fully recyclable
  • Tins – wash them out and they’re fully recyclable


You’ll paint up to 12 square meters of a smooth or planed timber surface (one coat) with one litre; rough sawn surfaces will take a lot more paint than a smooth surface so calculate on a coverage rate of approximately 6 square meters per litre for one coat.

Further coats take up a lot less paint than the first. If you’re using a sprayer then remember that there can be a lot more application wastage than using a brush.

Each paint can will treat approximately:

  • 750 ml           4.5 to 9.0 square meters
  • 2.5l                 15 to 30 square meters
  • 20l                  120 to 240 square meters