How do you stop stains showing through paint?

Short answer: fix the cause, let it dry, seal the mark, then paint

A stain stays gone when four things happen in order. Each step below comes from the makers' own instructions.

1. Fix the cause. Taubmans says that where water stains or leakage are present, the source needs to be fixed before you paint. Wattyl puts it plainly: paint can't solve moisture coming from behind or above the ceiling.
2. Let it dry. Taubmans says surfaces must be clean and dry before its stain blockers go on. Wattyl says to let the ceiling dry completely.
3. Clean off what you can, then seal the rest. Dulux says to remove as much of the stain as possible with sugar soap, sanding or scraping. What's left gets a stain blocker.
4. Topcoat once the blocker is ready. Dulux and Taubmans list recoat times from 45 minutes to 1.5 hours.

Notice where the blocker sits. Taubmans and Wattyl both put fixing the leak and drying the ceiling ahead of it.

Why stains bleed through ordinary paint: the mark moves up through the film

Stains bleed through when what caused them moves up into the new paint. Dulux describes tannin staining this way. It's the brownish or tan colour that shows on a painted surface when tannins move from the timber underneath up through the paint film. Dulux sells its High Opacity Stain Blocker on the same idea, saying it blocks stains from migrating through the topcoat.

So a stain needs a barrier coat between the mark and the topcoat. Haymes says an undercoat does that job for watermarks and smoke residue. Wattyl describes its Master Prep Spirit-Based Stain Blocker as a barrier coat that blocks stain transfer to the finish coat. Taubmans says its stain blockers seal stains and give a sound surface for topcoats.

Stain by stain: which blocker the makers name

Match the blocker to the stain. Here's what each maker's product page or data sheet names for the stains you'll find on walls and ceilings in most homes.

Notice how often the answer for water stains is an oil, shellac or spirit based product. Taubmans' own water based Mould Blocker data sheet sends water-based stains to its oil based Tough Stain Blocker instead. Dulux's Advanced Stain & Odour Blocker is the water based exception, and Dulux says it matches the stain blocking of an oil and shellac-based undercoat.

Oil, shellac or water based: how the stain blockers compare

Here's how they compare on base, clean-up and drying time. The clean-up line on the label follows the base. The oil based products here list mineral turpentine, Taubmans' shellac product lists methylated spirits, and Dulux's water based product lists water.

A few details from the labels change which one suits the job. Wattyl says Master Prep is for interior use only and goes under water-based or oil-based finish coats. Dulux says the spray's vertical nozzle makes it easy to use on ceilings. Taubmans lists coverage of up to 12 square metres per litre for Tough Stain Blocker and up to 14 for Fast Drying. And Dulux says not to tint its stain blockers when they're used to block stains.

Water stains on ceilings: the leak gets fixed and the ceiling dries first

A water stain on a ceiling means water got in, so the first job is finding out whether it's still getting in. Wattyl says to fix an active leak, plumbing issue or roof problem first. Wattyl also says to hold off painting a ceiling if you notice any of these:

• Soft or sagging plasterboard.
• Bubbling caused by water leaks.
• Persistent dampness.
• Brown water stains that keep reappearing.

If you see any of these, hold off painting and fix the cause first.

Fixing the leak is often someone else's licence. Sunshine Coast Council lists roofing (stormwater) as plumbing and drainage work, and says you need a licensed plumber or drainer for work other than unregulated work. The QBCC says all regulated plumbing and drainage work in Queensland must be done by a licensed plumber or drainer.

If water has reached a light fitting, fan or other wired item, leave it alone. The Electrical Safety Office says water-damaged equipment can cause electric shocks and fires, that you shouldn't do your own electrical work, and that a licensed electrician should check water-damaged hard-wired items.

How a stained ceiling gets repainted, step by step

Once the leak is fixed and the ceiling is dry and firm, the repaint follows the makers' instructions in this order. Our ceiling painting guide covers rolling the topcoat itself.

Older ceiling? Check with the regulator before you sand or scrape. Workplace Health and Safety Queensland licenses asbestos removal.

1. Check it's dry and sound. Look at the board around the stain. Wattyl says soft or sagging plasterboard means hold off painting.
2. Clean the stain back. Dulux says to remove as much of the stain as possible with sugar soap, sanding or scraping. If there's mould, Taubmans says to treat it with bleach or a mould treatment, then rinse with clean water. Wattyl warns against mixing bleach-based products with ammonia or other cleaners.
3. Scrape and fill. Dulux says to scrape off loose and flaking paint and fill holes and cracks before the blocker.
4. Test a small patch. Taubmans says to always test stain blocking and adhesion on a small area first.
5. Apply the blocker, untinted. Dulux says one coat of Advanced Stain & Odour Blocker, with a second sometimes needed on heavily stained paper-faced plasterboard. With the spray, Dulux says to use several light mist coats, and not to spray below 10 or above 35 degrees.
6. Wait the recoat time, then topcoat. Taubmans finishes its ceilings with two coats of Ceiling White.

Taubmans' data sheets add a ceiling safety line worth keeping. Wear safety glasses, don't paint directly overhead, and keep the room well ventilated.

When the stain is a job for a painter, or for a plumber first

Sealing one small, dry mark on a reachable ceiling is fair DIY. These are the jobs to hand over, and to whom:

• A leak that's still active, or a stain that keeps coming back. Find and fix the leak first. Sunshine Coast Council lists roofing (stormwater) as plumbing and drainage work, and says you need a licensed plumber or drainer for work other than unregulated work.
• Water near lights, fans or switches. A licensed electrician, as the Electrical Safety Office says.
• Soft, bubbling or sagging plasterboard. Wattyl says to hold off painting until that's sorted.
• Smoke marks across a whole room, or a full ceiling of old water stains. That's a full prep and repaint, with every mark sealed before the topcoats.
• Stairwells and high ceilings. Our room painting guide covers the ladder limits.

Paint goes on last. Sort the leak, the wiring and the board first. As Wattyl says, paint can't solve moisture coming from behind or above the ceiling.

What stain blocking means for your painting quote

Each stained area adds cleaning, a test patch, a sealing coat and its drying time before the topcoat starts. Our interior painting cost guide shows how wall condition changes the price, and our guide to painting a rental between tenants covers turnaround.

Our interior house painters work across the Sunshine Coast, and the suburbs we cover are on our locations page. We've painted Sunshine Coast homes since 1985 and hold QBCC licence 1281728. Get a guide price from our instant estimate, and we'll arrange a site visit if the job needs one.