Does anti-condensation paint actually work?
What the insulating additive in the paint does to a surface temperature, the situations where it genuinely helps, and why it cannot beat a serious cold bridge.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 3 min
Short answer
It does something real but small. The paint contains a lightweight insulating filler that slightly warms the painted surface and slows how quickly it drops below dew point, and most versions also contain a fungicide. On a marginal cold spot that is enough. On a genuinely cold uninsulated wall or a solid cold bridge it is not.
Anti-condensation paint gets treated as either a miracle or a con, and it is neither. It is a thin coating with an insulating filler, so the physics is straightforward: it adds a very small amount of thermal resistance right at the surface, which raises the surface temperature by a small amount. Whether that small amount matters depends entirely on how far below dew point the surface was sitting.
Step by step
- Work out how cold the surface actually is.An infrared thermometer on the cold spot, on the warm wall beside it, and a hygrometer reading of the room. If the cold spot is a degree or two below the dew point, a coating can bridge that. If it is five degrees below, it cannot.
- Fix the cause first where you can.Furniture off the wall, curtains clear of reveals, extract fans working, washing dried elsewhere. Paint is the last measure, not the first.
- Choose the product for the job.Some are insulating only, some are fungicidal only, and some are both. If you have had mould, you want the fungicidal property as well as the thermal one.
- Treat the existing mould before painting.Painting over live mould is pointless — it grows through. Clean with a fungicidal wash, let it dry fully, and then apply.
- Apply it to the whole cold surface, not just the mouldy patch.A patch leaves a boundary where the temperature steps, and mould reappears along the boundary.
- Follow the coverage rate exactly.These products only work at their specified film thickness, which is usually much heavier than an ordinary emulsion. Spreading it thin to make it go further removes the entire benefit.
- Judge it over a winter.If the mould still comes back after a properly applied coating, the surface is too cold for a coating to fix and the answer is insulation.
- Decorate over it correctly.Most require their own compatible finish or a breathable emulsion. A vinyl silk over the top can undo the effect.
Tips
- It is most useful on ceilings and in bathrooms, where the surface is only marginally cold and the moisture load is high and intermittent.
- It is least useful behind furniture on an uninsulated external wall, which is usually far below dew point.
- Do not confuse it with damp seal or stain block. They are different products for different problems and none of them are interchangeable.
Common mistakes
- Using it instead of an extract fan — The paint slightly raises the surface temperature; it does nothing about the litres of water going into the air. In a bathroom with no working fan, the moisture wins.
- Applying it thinly to save money — The thermal effect depends on film thickness. Under-applied, it is an ordinary emulsion with a fungicide in it.
Questions people ask
Is it the same as thermal or insulating paint for walls?
It is the same family of product. The claims made for exterior 'insulating paint' on heat loss are generally not supportable; the honest claim for the interior product is a small rise in surface temperature at the surface itself, which is enough to matter only where the margin was small.
Will it stop condensation on my windows?
No. Glass is glass and you cannot paint it. It may reduce condensation on the reveals and the window board next to the glass.
Can I use it in a rented flat?
Yes, as a redecoration, but if the underlying problem is a cold uninsulated wall or a missing extract fan, that remains the landlord's responsibility and should be reported rather than painted over.