Drying, Ventilation, Curing and Circulation

All Waterlox products are air-dry products. No hardeners, cross-linkers or heat are needed to properly cure or dry any Waterlox products. The only critical ingredient in the curing process is oxygen.

When applying finishes, there are two steps to the drying and curing process. This guide will specifically focus on time and air movement, but other environmental conditions may play a minor role. See the Environmental Conditions guide for more information on factors such as temperature, humidity and finishing outdoors.

Drying

Drying is the portion of the process when the solvents/carriers evaporate and leave behind the solids portion of the coating. The carrier solvents (or water) basically spread out all the solids molecules, so they can’t stick together and form a coating. This is for the traditional solvents like mineral spirits in our ORIGINAL, URETHANE and MARINE finishes, as well as the water in our H2OLOX product line. During this time, the coating will be “wet”. Dust/debris can get stuck in the finish or you can leave marks by touching the wet finish after it has started to set. The drying times for each product family are listed in the table below.

Ventilation

Depending on the finish used, there will be different ventilation needs. The definition of ventilation is the “provision of fresh air to a room, building, etc.”. This means removing “contaminated” air and supplying fresh air. When using more traditional solvent-based products (ORIGINAL, MARINE, and URETHANE), these solvent will evaporate into the surrounding air during the drying phase. These solvents should be exhausted to the outside. For water-based products (H2OLOX), the main solvent is water. To keep dust and debris down, ventilation and air movement should be kept to a minimum. For the high solids buff-in products (TRUETONE and UNIVERSAL Tung Oil Sealer), there is very little solvent, so minor ventilation is good and because they aren’t applied in very wet layers, there is very little concern about dust/debris getting stuck in the finish, so good air circulation is helpful.

Ventilation is most important during the drying phase and will usually last 2-4 hours (see table), after that you can continue to ventilate, but windows can be closed during inclement weather if need be.

Curing

Curing is the portion of the process when the solid particles that are left behind start to interact and react with each other to form the actual coating. For an in depth explanation of the curing process, view our The Curing Process guide. Oxygen molecules are pulled into the coating and small sections of polymer start to join together to create a large continuous, waterproof molecule over the surface of your project.

Curing is much slower than the drying process and can take a few hours to a few weeks depending on the products used. In general, the surface of the coating is well cured in a few hours, but as it’s harder for oxygen to make its way deeper into the film, it may take much longer for the entire film to fully cure. Ventilation (replacing the air in an area with fresh air) is less critical at this stage and it is more important to have air circulation.

Circulation

Air circulation is the critical ingredient during the curing process. If you keep the air moving, there is a more likely chance for an oxygen molecule to get to where it is needed. Standard HVAC is better than nothing, but it is not ideal at keeping air moving over the surface. A box fan (for larger projects) or small desk fan (for smaller projects) on a low setting will keep a constant supply of fresh oxygen molecules working their way over the project surface. This increases the likelihood of one being in the right place to make a new connection and therefore improves and accelerates the curing process.

While good circulation is critical in good curing, it can be detrimental if done too early. If your coating is still wet (in the drying phase) too much air movement can cause the very top surface to cure too quickly. This can actually extend drying times (solvents/water are trapped under the new film) and lead to issues like wrinkling, soft films and lingering odors. A quick check is to lightly touch the coating and see if you leave a finger print. If no print is left, it is OK to begin circulation.

¹Dry To Touch (DTT) – The dry to touch time is the amount of time until “no pronounced marks left by finger touching the film” (ASTM D-1640). This means that the coating will not stick to a finger, nor will a permanent finger print be left in the wet film. This does not mean you should cover or walk on the surface. You may be able to cross the surface with socked feet, but avoid if possible.

²Abrade After – This column describes when to sand/buff/abrade a film. Abrading is required for the Urethane products after 12 hours to improve adhesion. When the coating is <12 hours old, it is still curing and chemically active enough to bond well with the next coat. After 12 hours, the surface may be too well cured to create a strong bond with the next coat. Abrasion helps to create a better profile for adhesion. A slight buff/abrasion is good for the H2OLOX products to ensure good adhesion and a smoother final film. DO NOT ABRADE the non-film forming products as there is nothing on the surface to abrade. This will simply abrade the wood or remove color. ORIGINAL and MARINE finishes do not require any sort of abrasion for performance, but a light sanding can be done if desired. See the tips for a smoother final finish guide for more information.

³No film formed, “immediate” – These products (UNIVERSAL Tung Oil Sealer, TRUETONE, and PURE Tung Oil) do not leave any product on the actual surface of the wood, therefore, there is no real film to leave a mark in. There will be a slightly oily feel for as long as a few days, but there should be no appreciable layer or transfer of oils after the excess has been buffed off. If there too much oil, rebuff with a fresh towel, rag or pad to remove more excess. Some “bleed back” may occur over the first few hours as oils may creep back out of cracks or certain parts of the wood and will look like shiny spots. Wipe these off with a clean rag/towel/pad. Even though these coatings are essentially “dry” immediately, you should stay off the surface and do not cover. Although not truly dry, you can immediately walk on the surface with socks or protected shoes. Avoid bare feet or unprotected shoes for at least 24 hours.