How Does Paint Dry? The Practical Implications of Paint Wicking for Professional Painters Reply

Luis had been out sick for three days when he finally returned to finish the job. The client was glad that Luis was feeling better and eager to see the job finished. All that remained was touching up the wall near the trim. Luis had a steady hand and was sure the client would be excited with the final result.

However, after finishing all the corner-work and trim work, Luis started to notice that the paint appeared to be a different color than the rest of the wall. The difference was subtle and it was unlikely anyone, including the client, would ever notice. But Luis noticed, and it aggravated him. As he lay in bed ill for the previous three days, he had worried that this might happen. Some of the paint he applied today was actually going over the paint from earlier that had already dried. And that was causing a problem.

Paint drying differently

Paint from the same source can dry very differently.
Image courtesy of MaisonDepax.com

As we recently discussed, getting a new coat of paint to match an older coat is a challenge. That challenge isn’t limited to paint colors that have faded after years of exposure to sunlight or everyday wear and tear. Paint that is just a few days old can differ greatly in color compared to a new coat. Finding the right paint color and gloss in relation to the paint you are trying to match takes a well-trained eye and an experienced paint technician with the right tools at their disposal. However, the right color and sheen aren’t the only critical parts of matching paint colors. There is also the matter of the paint’s rate of absorption into the substrate.

By definition, a dried or cured paint is one that has set up completely and is absent of any water or liquid composition. Water in paint is removed one of two ways after application. The primary removal of water takes place through atmospheric evaporation. The secondary way that water is removed is through “wicking,” or the absorption of water into the substrate. That different substrates absorb water from paint at different rates has a material affect on the final appearance of the paint.

What does this have to do with matching colors to existing paint? Simple: the original paint was applied to a different surface than the new coat, which means it will dry at a different rate. And since the time to dry or cure affects the appearance of the paint, two identical paint colors may look very different after drying, depending on the surface to which they are applied.

paint drying on interior wall

A wall showing how the same paint can dry differently.
Image courtesy of LaurenPlayingHouse.com

Consider an interior wall. The original paint coat was likely applied on top of a primer on top of sheetrock. The touch-up coat you apply years later is actually being applied on top of the paint, which has significantly different hardness and absorption qualities than the sheetrock/primer substrate that took on the original coat. As a result, even if you are using the exact same paint for the original coat and the eventual touch-ups, the final appearance may look different. The original paint surface (sheetrock and primer) absorbed the moisture in the paint more quickly than in the case of paint-on-paint. After drying, the touchup paint is likely to appear slightly darker than the original coat, even if the paint is from the exact same can.

While controlling the rate of moisture absorption with any certainty is virtually impossible, you can control the time paint takes to dry in an effort to manipulate the curing process. By extending the time a paint takes to set, you may be able to more accurately match the color with an existing coat and avoid having a noticeably different result in your touchups. For example, thinning the paint with water or thinner will give the paint a longer time to dry and set up. Similarly, there are a number of commercial additives available to help control drying time in paint.

thinning out industrial paint with water

Thin out your paint to increase wicking time.
Image courtesy of Wikihow.

Manipulating drying time or paint-set time is but another tool in your arsenal when it comes to matching paint colors. Whether matching an older paint in the case of touchups or simply trying to ensure that the paint on your draw-down card accurately matches the end result of your work, do not overlook the importance of wicking when you work. Click here to learn more about matching paint colors!

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