Our general rule of thumb is to wait 24 hours between coats of Waterlox Original Tung oil finishes. There are two basic steps to the drying and curing of a Waterlox Original Tung oil finish and the dry times may vary depending on a number of factors, such as ventilation, humidity, temperature, substrate and size/scope of project. Please view the Ventilation Guide for more information and details.
- The first step is the evaporation of the solvent "carrier" system. The evaporation of solvent usually occurs in the first 2 - 4 hours with proper cross-ventilation techniques.
- The second step is the curing of the solids system, which is comprised of the oil and resin. The solids system completes 95% - 98% of its cure cycle in 7 – 14 days with proper ventilation; full cure, film hardness and chemical resistance properties are achieved in 30 - 90 days with continued adequate ventilation.
Ventilation. Proper ventilation and adequate air circulation must be provided when using any wood finishing materials. Most oil-based varnishes, including Waterlox, dry upon exposure to oxygen, which is also known as “oxidative cure.” A lack of cross-ventilation (air exchange) provides less free oxygen, slowing the drying process. Cross-ventilation is the biggest factor affecting dry times. It is not recommended that any solvents or solvent-based materials be used in a non-ventilated area. It is the oxygen molecules in the air that interact with the varnish, creating a chemical reaction and causing the film to dry. Therefore, the better the ventilation (during and after all coats) the quicker the film obtains its final hardness and other properties.
ASHRAE (The American Society of Heating, Refrigerating and Air Conditioning Engineers) states that the typical air exchange in a residence using only mechanical HVAC can be as low as 0.35 air exchanges/hour. In most cases 0.35 air exchanges/hour will not be adequate to dry Waterlox in 24 hours. We therefore strongly suggest achieving a gentle flow of air by cross-ventilation. This can be achieved by the use of a box fan running at low-speed in a window or door exhausting to the outside air as well as an open window in some other part of the room or house to achieve 3 - 4 air exchanges/hour. Not only will this aide the drying process by pulling in fresh air loaded with oxygen, but it will exhaust the solvent odor.
Read the directions on the label completely before using. Lingering odor indicates inadequate ventilation, high humidity or both.If you cannot ventilate the area choose another product.
Humidity. In high humidity situations, ventilation is even more critical. High humidity will impede the drying process because there is less free oxygen in the atmosphere; therefore, the lower the humidity, the better the drying conditions.
The softer the wood, the longer it may take to dry. (See how your hardwood measures up on the wood hardness/Janka scale FAQ
). Softer woods absorb finishes deeper into the wood fibers. This deeper penetration leads to slower drying because of less exposure to oxygen. The opposite would be true in a harder wood, if the finish sits on top of the wood fibers it will dry slightly faster.
Many of the hardest and densest woods (e.g.: ipe, Brazilian cherry, Brazilian walnut, paduc, rosewood, cypress, etc.) come from either rainforests or swamps. Their density and natural oils prevent them from rotting in their humid native climates. These same characteristics that prevent them from rotting in their natural habitats are also what make them more difficult to finish. When you apply finishes to these types of woods, the solvent resolubalizes the oils in the wood which can slow down the drying process because the driers in the formulation are now needed to dry the finish AND the naturally occurring oils in the wood. We’ve found rainforest/swamp woods may require more than 24 hours of dry time (Review the Cure Time FAQ and the tips below for methods on how to determine if the substrate is dry.)
If you are experiencing abnormal drying (e.g. coat of finish is tacky and not dry in 24 hours) you can perform a simple test to determine if the substrate is causing the slower than normal dry time. Apply a coat of the finish that is not drying to a piece of glass and wait 24 hours. Glass is used as a control because it has zero porosity and does not vary in porosity like wood. If the finish dries normally on the glass in 24 hours, but for some reason is not drying at the same rate on the substrate, you have proved that there is some type of reaction/influence with the substrate that is causing it not to dry properly.
Temperature. Although temperature is still and important factor, it bears the least affect of all the factors of drying. Waterlox dries through oxidation as mentioned in the ventilation section. Oxidation is a reaction. Most reactions happen faster in warmer temperatures because the molecules/atoms are more active.
In many cases, cold/winter weather is almost always accompanied by lower humidity. So, applications completed in 30° F with 10% humidity and some ventilation will dry faster than an application in 90° F with 90% humidity and no ventilation.
Coat Number. Even though a coat of Waterlox Original Tung oil finish might be dry enough to re-coat in 24 hours, it is not completely cured through. Because of this phenomena, as you build coats, it may take longer than 24 hours to dry. Therefore, dry time may increase for each additional coat applied.
- Larger projects may take longer to dry than a jewelry box for example due to the size/scope of the project.
- You can check to see if your surface is dry by two methods:
- Take a piece of facial tissue between your finger and the substrate and press down firmly. Lift up on the facial tissue. If any fibers of the facial tissue are left in the film, the film is not dry yet and needs more time.
- Lightly sand an area of the project, if it powders and does not gum or plug the sandpaper, then it is dry enough to re-coat.