How To Stop Stains Coming Through Paint

To stop stains coming through paint, fix whatever caused the stain, let the surface dry fully, clean it, and seal the mark with a stain blocking primer before you repaint. Ordinary emulsion will not hold back water marks, nicotine, smoke, grease or wood tannin, however many coats you apply, because the stain simply dissolves into the new paint and reappears as it dries. A primer designed to block stains locks the mark beneath a barrier so the topcoat stays clean.

The type of primer matters. Shellac based primers block the widest range of stains, including the stubborn ones, while water based stain blockers are easier to use and suit lighter marks. The right choice depends on what caused the stain and where it is, which is what this guide covers.

Why stains bleed through emulsion

Most stains that come back through paint are water soluble. When you roll on a water based emulsion, the water in the paint re-wets the stain underneath and draws it up into the fresh coat. As the paint dries, the discoloration settles on the surface again, often looking exactly as it did before you started.

Tikkurila’s guidance on painting over water stains puts it simply. Applying a topcoat without a stain blocking primer will not stop the stain coming through again. The same applies to nicotine and smoke residues, grease, felt tip and crayon, and the natural tannins in some timbers.

From working with clients across Kent over more than 30 years, a recurring pattern is a ceiling that has been repainted three times over a water stain that keeps returning. No number of emulsion coats will fix it. One coat of shellac primer will. In our experience, a single coat of the right stain blocking primer works better than extra coats of emulsion because emulsion carries the stain up with it, while the primer forms a sealed layer the stain cannot pass through. The jobs that fail are almost never down to the brand of paint. They are the wrong product on the wrong surface.

Common stains and what causes them

• Water stains. Brown or yellow rings on ceilings and walls, left behind by a leak from a bath, pipe, roof or overflow.
• Nicotine and smoke. A yellow or brown film across walls and ceilings, usually heaviest above where someone sat or near a fireplace.
• Soot and fire damage. Dark staining, often with a lingering smell.
• Grease. Common in kitchens and around light switches and door handles.
• Tannin and knots. Brown or orange marks bleeding through paint on new or stripped timber, especially over knots.
• Pen, crayon and marker. Children’s artwork is a regular one, and permanent marker is particularly stubborn.
• Old mould staining. A grey shadow left behind after the mould itself has been killed.

Step 1, fix the cause first

A stain is a symptom. Before any decorating, find out where it came from and make sure it has stopped. Ronseal’s advice on damp stains is that you always need to find and fix the problem causing the damp before covering the mark.

For water stains this is critical. Painting over a ceiling that is still getting wet only hides the problem until the next leak, and it can trap moisture in the plaster. Zinsser’s guide to painting water stained surfaces says the moisture content should not exceed 12 per cent before painting. In practice that means waiting days or even weeks after a leak, depending on how wet the ceiling got and how warm and well ventilated the room is.

A useful first question about any ceiling stain is what sits directly above it. A bathroom, a radiator pipe, a loft tank or a section of roof will usually point you to the source.

Step 2, clean the surface

Primers need a clean, sound surface to bond to. Wash stained walls and ceilings with sugar soap or a dedicated degreaser, rinse with clean water and let everything dry fully. This is especially important for nicotine, smoke and grease, where the surface carries a film that can stop primer adhering properly.

Kitchens deserve particular care. Cooking grease builds up invisibly over years, and on painted kitchen cupboards we’ve found that grease left on the surface causes more failed paint than any other single thing. The same is true of kitchen walls and ceilings.

Scrape off any loose or flaking paint around the stain and lightly sand the edges so the repair blends in.

Step 3, choose the right stain blocking primer

Shellac primers for the toughest stains

Zinsser B-I-N is a shellac based primer sealer that blocks water, smoke, nicotine, tannin, oil and marker pen stains, and seals odours from smoke and pets. Zinsser says it dries in 15 minutes and is recoatable in 45 minutes. It is the product we reach for when a stain has already come back through ordinary paint, and it is one of the primers professional decorators rely on for problem surfaces.

Shellac primers do have drawbacks. They have a strong smell, are flammable, and brushes are cleaned with denatured alcohol (methylated spirits) or an ammonia solution rather than water. They are intended for interior use, apart from spot priming knots, sap streaks and rust stains outside.

Solvent based stain blockers

Oil and alkyd based primers such as Zinsser Cover Stain and Johnstone’s Trade Stain Block Primer seal water, smoke, nicotine and tannin stains and can be used inside and out. They take longer to dry than shellac and need white spirit for clean up.

Water based stain blockers

Water based options are lower in odour and easier to work with. Dulux Trade Stain Block is a water based primer and topcoat for interior walls and ceilings that covers marks from inks, crayon, coffee, grease, water and nicotine. Zinsser B-I-N AQUA is a water based version of their stain blocker that Zinsser says blocks nicotine, smoke, water, grease and tannin stains.

Not every water based primer is designed for the hardest jobs, though. Zinsser itself points heavy water stains and fire and smoke damage away from its standard Bulls Eye 1-2-3 towards stronger products. If a mark is severe, or has already bled through once, a shellac primer is the safer choice.

Aerosols for small marks

For a single small water ring or a pen mark, a stain block aerosol is quick and tidy. Polycell’s One Coat Stain Stop aerosol, for example, is designed for pen, grease, nicotine and soot marks on painted plaster. On larger areas an aerosol tends to leave an uneven patch, so a brushed or rolled primer gives a better finish.

Step 4, prime properly

Apply the primer over the whole stain and a little beyond its edge. For widespread nicotine or smoke staining, prime the entire wall or ceiling rather than patching, because the staining is rarely confined to what you can see. Let the primer dry for the full time stated on the tin before you go any further, and allow longer over heavy stains if the manufacturer advises it.

Ventilate well, especially with solvent and shellac products. HSE guidance on solvents notes that exposure can cause headaches, dizziness and irritation, that ventilation is always required, and that the more enclosed the space, the greater the risk. Open windows and doors and keep the room clear of anyone not working.

Step 5, repaint

Once the primer has dried, apply two coats of your chosen finish over the whole wall or ceiling, not just the primed patch. Painting only the stained area usually leaves a visible difference in sheen and colour, particularly on a white ceiling in daylight.

Stopping knots and tannin bleeding through woodwork

On bare or stripped timber, resin and tannin in knots can push brown marks through new paint weeks or even months after the job is finished. The fix is to seal knots before priming. Traditional knotting solution is shellac based and is applied directly onto each knot, and Johnstone’s Trade says its knotting solution seals in knots and sap streaks and prevents topcoat discolouration. Shellac primers such as B-I-N can also seal bleeding knots and sap streaks.

When we prepare timber doors for painting, every knot on bare wood gets knotting solution before the primer goes on. It takes a few minutes and saves a brown ring reappearing through a freshly glossed door.

When to call in a decorator

A single small water mark is a straightforward DIY job. It is worth getting professional help when the staining covers whole ceilings or rooms, when it has already bled through more than once, after fire or smoke damage, or where you are not sure the leak has been fixed. Heavy nicotine staining throughout a property usually means every ceiling and wall needs cleaning and priming before any colour goes on.

Conclusion

Stains come through paint because emulsion cannot hold them back. Fix the cause, let the surface dry, clean it, then seal the mark with a stain blocking primer, using a shellac based product for anything stubborn. Finish with two full coats and the stain will stay where it belongs.

If you have a stain that will not stay hidden, A-Z Decorators can find the right primer for the job and leave a clean, lasting finish as part of our interior decorating across Kent. Contact us for a free quotation.