Repainting a home after flood or storm water damage is not the same as a regular interior repaint. Water that has sat in walls, subfloor cavities or ceilings for even 24 hours changes the surface chemistry, invites mould growth and can compromise plaster bond. Skip the drying and treatment stage, and the new paint film will blister, peel or grow dark staining patches within a season. Melbourne homeowners who go through this process often repaint twice because the first attempt skips the steps that actually matter.
What water damage actually does to painted surfaces
Water doesn't just stain. It softens plaster binders, wicks salts to the surface and breaks the adhesion between the existing paint film and the substrate underneath. When the surface dries, those salts crystallise beneath the paint and push it away from the wall. That's why a wall that looked fine after it dried suddenly shows bubbling and flaking three weeks later.
In older Melbourne homes with lath-and-plaster walls, the timber lath swells and can crack the plaster face. In homes with modern plasterboard, prolonged saturation causes the paper face to delaminate. Both need different repair approaches before any paint touches them. Identifying which substrate you're dealing with is the first practical step.
Drying before painting: the number that matters
Plasterboard and render need to reach a moisture content below 15% before you prime. Use a pin-type moisture meter, available from most hardware stores, to confirm this. Don't guess by touch. Walls that feel dry to the hand can still read 25–30% on a meter, and applying primer at that moisture level traps water behind the film.
In Melbourne's climate, drying a flood-affected room naturally takes 2 to 6 weeks depending on season, ventilation and how deep the saturation went. Dehumidifiers and industrial fans cut that time significantly. Running a dehumidifier in a closed room is more effective than open windows in humid weather. Check the meter daily, not weekly.
Mould treatment before any primer goes on
If water sat for more than 48 hours, treat the surface for mould before priming. It doesn't need to be visibly black to carry spores. A diluted bleach solution (1 part bleach to 10 parts water) applied by brush and left for 10 minutes kills surface mould on most substrates. Rinse thoroughly and allow the surface to dry completely before proceeding.
For walls where mould has penetrated into the plaster itself, a single wash isn't enough. Those sections need cutting out and replacing. Painting over contaminated plaster with a mould-resistant topcoat does slow re-growth, but it doesn't eliminate the colony underneath. The paint fails, and the mould returns. Cut it out. It's a harder job, but it's the only one that holds.
Priming after water damage: don't use a standard primer
A PVA or water-based primer applied to a water-damaged surface will reactivate the salt deposits and lift the surface again. Use a shellac-based primer, or a high-build oil-based alkali-resistant primer, for the first coat on any surface that was submerged or heavily saturated. These products seal the salts in place rather than dissolving them.
Dulux Wash&Wear primer and similar water-based products are fine for unaffected areas in the same room. Don't use them on the damaged zones. Use two coats of the shellac or alkali-resistant primer on those patches, then a coat of water-based undercoat over the whole wall to unify the sheen before the topcoat goes on. This three-product approach adds time but eliminates the patchiness that plagues most post-flood paint jobs. You can read more about handling bleed-through from water stains in the article on how to paint over water stains without them bleeding through, which covers primer selection in detail.
Choosing the right topcoat for flood-affected rooms
After flooding, many homeowners upgrade to a washable, low-sheen acrylic for the main walls. That's a sound choice. A low-sheen finish hides minor surface irregularities that remain after patching, and a washable formula tolerates the cleaning that often follows a flood event. A flat or matte finish looks better fresh but shows every repair line and scuff mark in sharp relief.
For rooms that had standing water, consider a topcoat with a built-in mould inhibitor, such as Dulux MouldShield. This won't compensate for skipping the mould treatment step, but it does slow re-colonisation in rooms that remain prone to humidity. Bathrooms and laundries affected by stormwater are the most common candidates.
Ceilings after a roof leak or ceiling penetration
Storm damage that enters through the roof creates a different problem to wall flooding. Water tracks along joists before it drops, which means the staining on your ceiling may be a metre away from where the water actually entered. Don't prime only the visible stain. Probe the ceiling with a moisture meter across a wider area before you decide how much to treat.
Plasterboard ceilings that have bowed or softened under water weight need replacing, not just priming. A bowed sheet won't recover its flatness once dry. Patching a bowed sheet and painting over it delays the inevitable. If you're dealing with extensive ceiling damage, it's worth reading the full guide on how to handle paint damage after a roof leak before you start.
Skirting boards, door frames and joinery
Timber joinery that has been wet needs the same drying protocol as plaster walls. Swollen skirting boards should be left to dry in place before you assess whether they need replacing. Timber that looks warped when wet often straightens as it dries. If it doesn't straighten, replace it. Painting over warped skirting boards locks in the distortion.
Sand back any raised grain on timber joinery after drying. Use a 120-grit to knock back the fibres, then a 180-grit to smooth. Prime with an oil-based undercoat before applying a water-based topcoat. Water-based undercoats raise the grain again on timber that has been saturated, which defeats the preparation you just did.
Sequencing the job so you don't redo work
Work from top to bottom. Treat and prime ceilings first, then walls, then skirting boards and joinery. Ceiling repairs inevitably drop dust and debris onto walls. If you've already finished the walls, you're cleaning and touching up again. The sequence also lets you identify any bleed-through on ceilings that might track down to walls before the wall paint goes on.
Wait a full 24 hours between the shellac primer coat and the water-based undercoat. The shellac needs to cure completely before a water-based product goes over it. Rushing this stage is where most DIY post-flood paint jobs develop adhesion failures within the first year. Patience at this stage is genuinely the difference between a job that holds and one that doesn't.
If the flood or storm event was significant and multiple rooms are affected, it's worth getting a professional assessment of the surfaces before committing to paint. Apex Painters Melbourne handles post-flood repaints across Melbourne and can advise on surface condition, product selection and sequencing for homes that need a systematic approach rather than a room-by-room patch.