Why has my varnish gone cloudy or milky?
Cloudiness in varnish is trapped moisture or trapped air, and which one it is decides whether it will clear on its own or has to come off.
- Difficulty
- beginner
- Time
- 30 min
- Read
- 3 min
Short answer
A water-based varnish that looks milky in the tin or while wet is normal and clears as it dries. Cloudiness that is still there when the film is hard is moisture trapped in the coating or in the wood, or a coat applied over one that had not cured. Trapped moisture sometimes clears with warmth and time; the rest does not.
Water-based varnishes are white in the tin and dry clear, so a certain amount of milkiness during application is expected and alarming to people who have not seen it before. The problem is telling that harmless stage apart from a genuine fault, and the test is simply whether it is still cloudy once the film has fully hardened rather than merely dried to the touch.
Step by step
- Give it longer before deciding anything.Water-based varnish can look faintly milky for a day or more in cool or humid conditions. A film that is not yet fully coalesced is not a fault. Wait until it is properly hard before judging it.
- Work out whether the cloudiness is in the film or under it.Look at it from a low angle in good light. Haze that sits in the coating tends to be even. Cloudiness that follows the grain, or appears in patches matching where you worked, is usually moisture in the timber or in a layer below.
- Consider what the conditions were when you applied it.Cold, damp air and high humidity are the main causes. Varnishing in an unheated room in winter, or in a bathroom, or outdoors late in the day as dew begins to fall, all trap moisture in the film.
- Rule out recoating too soon.A second coat over one that had not cured seals solvent or water into the first. That produces a haze that will not clear, and it is the most common cause on a job that went on quickly.
- Try gentle warmth and airflow before anything drastic.Warm the room steadily and keep air moving for a few days. Moisture-related bloom on a recent coat will sometimes clear as the film finishes curing. Do not apply direct heat.
- If it is still cloudy when fully hard, take it back.Sand the affected coats off and start again in better conditions. Nothing applied on top of a cloudy film makes it clear, and another coat usually deepens the haze.
- Check the wood is dry before recoating.If the timber itself is damp — an exterior door after wet weather, or a floor that was mopped — varnishing seals that moisture in. Give it days, not hours.
Tips
- Never shake a tin of varnish. Stir it slowly. Shaking whips in air that shows as a fine haze of bubbles in the film.
- Bathroom and kitchen jobs are worth timing for a dry spell with the extractor running rather than doing on the wettest day of the week.
Common mistakes
- Judging a water-based varnish while it is still wet. — It is meant to look milky at that stage. Judging it early leads people to strip a finish that would have cleared.
- Adding another coat to hide the cloudiness. — The haze is in the layer below and stays visible through the new coat, which now has to come off too.
Questions people ask
Will it clear on its own?
Sometimes, if it is moisture and the film is recent. Warmth and ventilation over several days is the test. Haze from recoating too soon will not clear.
Does the same thing happen with oil-based varnish?
Less often, and it usually looks different — oil-based varnish tends to bloom rather than go milky, often after being applied in cold damp conditions.