When painting, dry time varies according to several elements. Knowing these variables enables you to appropriately prepare for exterior paintwork and the time required on each coat before recoating or using the surface.
Type of Paint
The external paint applied significantly contributes to the drying periods. Solids, binders, and solvents in different formulations for paints affect the rate at which they cure.
Latex paints: These can be exterior paints that contain latex, meaning either acrylic or vinyl polymers, and water is then added, resulting in a shorter drying time of two to four hours between reapplications. However, latex paint takes longer than oil-based paints to achieve its ultimate cure and acquire its shield characteristics.
Oil-based/ Alkyd Paints: These paints are alkyd type with alkyd resins in the solvent of mineral spirits that need six to 24 hours between two coats but cure more in later hours. This is because the oil binders of the paint harden and create a denser layer when the paint is dry.
Enamels are some of the highest gloss oil/alkyd paints that take longer to dry and cure, starting with at least 24 hours of wet time between coats because of high solvent content.
Environmental Conditions
Exterior paint hardens by oxidization or coalescing, which results from the evaporation of solvents. Hence, external weather conditions are a factor that significantly influences the drying rate of exterior paints.
Temperature
The weather affects paint; it dries faster during warmer weather. High temperature is beneficial at accelerating the rate at which solvents evaporate and binders cure while at the same time being disadvantageous.
While at moderate temperatures of 60-80° F, the exterior latex paint can take one to two hours, while with an oil-based paint, the enamels take six to 12 hours to dry. When paint is applied in conditions of cooler temperatures, 50-60°F, or high humidity, it can take a lot longer to completely dry.
Direct Sunlight and Ventilation
Solar exposure increases the speed at which paint dries when there are solvents. Ventilation plays a vital role in effective drying and solvent removal.
Low mobility of air current, high amounts of shade, or low temperatures mean that more extended periods of time for coats to dry will be necessary. This also leads to tackiness or improper curing.
Paint Thickness
If excess paint is used in one coat, drying times may be significantly affected, and the paint may not cure correctly. Excessive thickness of paint coats will prevent solvents from proper evaporation whereas this would not be an issue if thinner coats of paint were used.
Evaluate the wet film thickness to be within the suggested levels provided by the manufacturer for best results. Usually, one to four mils of thickness are sufficient for one coat of paint.
Surface Porosity
The speed at which the base surface material absorbs water plays a crucial role. That is why paint takes longer to dry on porous surfaces such as wood, due to such surfaces absorbing the paint faster. It is easier for a coating of paint to dry where the substrate does not absorb the solvents found in the coating.
Before painting, the substrates should be cleaned adequately, sanded, or primed and painted according to the manufacturer’s application recommendations.
Number of Coats
Generally, the total curing time for different layers of exterior paint should be longer in between coats. Also take note that the first coats of stucco dry more slowly than the finished coats. Heeding the correct drying times is crucial for ensuring every coat dries well.
Tack-Free vs. Fully Cured
It is crucial to determine when paint looks and feels dry and when the chemical curing of the paint is complete.
Tack-free times specify when a subsequent coat of said material can be applied or when the coated surface will be only slightly sensitive to traffic. However, it may undergo considerably prolonged hours to attain the crosslink density, mainly the protective film characteristics.
Recoating Too Soon
Touching up exterior paint while its film is not fully formed will lead to some issues, such as a lack of adhesion, tacky feel, paint cracks, paint chalking, and lack of protection.
Another strategy for painting is to adhere to the manufacturer’s recoat window. When recoats are applied too quickly, the chance of paint failing to cure in the future also rises rapidly.
Testing Dryness
A few hours after painting is completed, it may be difficult to tell through observation whether exterior paint is already dry enough for another coat or application.
There are some simple methods to test dryness:
Touch Test
Gently rub a finger on a section of the painted surface. If it is slightly sticky, slippery, or leaves a stain behind, you will need to allow for more dry time.
Twist Test
Allow a piece of plastic wrap to stick directly to an area of the painted surface for 10 to 15 seconds. Gently tear it, and then observe the back side of the plastic sheet. The presence of a wet or tacky paint surface means that it is still too early for a recoating job.
Thumb Print Test
Apply gentle pressure with your thumb by pressing it into the painted surface, and then pull it back to see if your thumb leaves imprints that can be felt. If it has cured, pressing into the paint will cause it to bounce back without causing any indentation on the surface.
Why should one protect exterior paint when it is curing?
The paint should not come into contact with rain, grease, chemicals, or excessive dirt and should not be used often during the periods of curing. Make sure that exterior paint coatings develop a good crosslink density by allowing the coats to gain their total crosslink density. This takes between seven to 14 days before the coats of paint are exposed to standard atmospheric conditions.
It’s also wise not to plant gardens, add mulch, hang lights or signs, or do any other surface preparation before the paint has fully cured. Ensure that you know the different factors that influence exterior paint dry time, the weather conditions that allow it to dry faster, or conditions that allow paint to adhere to the right recoat window for long-lasting, quality exterior paint.
