A varnish coat will protect a wooden surface. But, the sealant has to dry and cure before it can protect a surface. So, how long does varnish take to dry?
On average, water-based varnish takes 6 hours to dry for a re-coat and 72 hours to cure. In comparison, oil-based varnish takes 24 hours to dry for a re-coat and 1 week to cure.
However, the ambient temperature, humidity, type of wood, and the number of coats determine its dry time. For example, if you apply it at a humid and cool temperature, it takes longer to dry.
Dry Time Between Coats
Varnish must dry for at least 6 hours between coats. The dry time between coats referees to the time to wait before applying another coat over it. On average, water-based varnish dries enough for a re-coat in 6 hours, while oil-based varnish takes 24 hours to dry between coats.
The reason water-based varnish dries faster is that it uses water as its solvent. Since water evaporates from the coating faster than oil, the water-based type dries faster than oil-based varnish.
To know if the coating is dry enough for a re-coat, feel the texture of the finish. If it feels sticky to the touch or gummy on the fingers, it hasn’t dried enough.
You can also know if the coating is dry enough by using fine-grit sandpaper. Swipe fine-grit sandpaper over the finish; if it gets clogged, the finish isn’t dry enough. If the sandpaper moves smoothly, the varnish is dry,
Or, you can check the container to know the exact dry time between coats.
Varnish is Dry When:
- When is no longer sticky or tacky.
- If its coating is hard.
- When you can sand it.
- If its coating looks shiny, not wet.
- If it reveals the wood grain.
Related Read: Polyurethane Dry Time?
Cure (Fully Dry) Time
It takes varnish between 24 hours and 1 week to cure. The water-based type cures within 24 hours, while the oil-based type takes 5 days to 1 week to cure. However, you must leave it to harden for 1 week before you use it.
Its cure time depends on the temperature and humidity. Its curing process is based on oxidization, while the drying process is based on evaporation.
For varnish to cure, the dry air (oxygen) has to get into the coating and cause the paint particles to oxidize and harden. After the paint particles become hard, the sealant cures. Once it cures, you can sand, clean, and use it.
If you clean or use it too soon, you can damage the finish. If the paint particles aren’t hard enough, the finish will be weak. You can remove a weak varnish coating by sanding or using water. So, always wait for it to cure before using it.
How To Speed Up Varnish Dry Time?
This guide will show you; 5 methods to make it dry faster, the tools you need, and how to do each method.
1. Using A Hairdryer
Since the sealant dries through evaporation, you can increase the heat around its coating to make the solvent evaporate faster. Here’s how to do it:
- Turn on the hairdryer.
- Set the heat to medium.
- Hover the hairdryer around the varnish coating for a few minutes.
- Crank up the heat.
- Move the hairdryer over the coating one last time.
- Turn off the hair dryer and let the coating dry for about 4 hours before recoat.
You shouldn’t fully dry it using a hairdryer. If you do, the paint particles won’t harden naturally, so the finish will peel off.
2. Using Paint Thinner
You can use a paint thinner to make it dry faster. This works for oil-based varnish, and you must do it before applying it. Oil-based varnish takes longer to dry because it has a thicker coat. So, if you thin it and apply lighter coatings, it will dry faster.
To thin oil-based varnish, use turpentine, mineral spirits, or paint thinner. To thin water-based varnish, use water.
Here’s how to do this:
- Get a clean paint bucket.
- Pour the varnish inside the bucket.
- Add paint thinner to the sealant (you can thin it up to 50%).
- Stir the mixture for 90 seconds (stir gently).
- Test it on a small area of the wood to see how it dries.
You shouldn’t over-thin varnish because the finish will be inconsistent and weak.
3. By Improving Air Flow
Since varnish dries through evaporation, you can increase the evaporation rate to speed up its drying time. To increase the evaporation rate, you must improve the airflow around the coating. Improving air flor also makes the sealant cure faster.
Here’s how to do it:
- Open all windows, doors, and air vents.
- Turn on the fans and direct them toward the coating.
- Set the air conditioner to “blow” or “fan.”
Here are a few other things you can do:
- Turn on the dehumidifier to reduce moisture content in the air.
- Only apply the sealant if the ambient or room temperature is above 60 degrees.
- Only apply it when the humidity is at or lower than 50%.
- Don’t apply it during the cold winter months.
- Thin it before applying it.
- Apply light coats.
Different Types of Varnishes
Spirit varnish dries in less than 24 hours. It dries faster than oil-based varnish because it has no oils in its formula. It is made from resin, solvent, and alcohol. But, it takes longer to cure (5-7 days).
Acrylic varnish dries enough for a re-coat within 12 hours and cures within 24 hours. It is water-based and has one of the fastest dry times because it contains a low amount of oils.
Exterior varnish dries enough for a re-coat within 24 hours. It is formulated with extra oil and chemicals to reinforce its finish to thrive in harsh exterior environments. The extra chemicals and oil make it thicker and increase its drying time.
Exterior varnish air dries, meaning it dries based on exposure to dry air. Since exterior varnish is used outdoors, its coating is exposed to a lot of dry air, so it dries to touch fast. But, even when it is dry to touch, it’s still not strong enough to hold another coat. Therefore, you must wait 24 hours before re-coating it.
On average, polyurethane varnish dries enough for recoat in 24 hours and cures in 3 days. Polyurethane varnish is oil-based, so it takes longer to dry. Also, it is a combination of two slow-drying finishes; polyurethane and varnish.
Normal polyurethane takes a few hours to cure. But, when you combine polyurethane with varnish, the dry time increases.
Depending on the type, varnish can take several hours to days to dry and cure. Oil-based varnish takes 24 hours to dry, while water-based takes 6 hours to cure.
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,