Why Does Caulk Turn Yellow

Yellowing caulk signifies a problem leading to seal failure due to cracking and shrinking. It must be replaced because the gaps it seals are less protected and more susceptible to damage. But why does it turn yellow if the caulk is made for the applications indicated on its label?

Caulk turns yellow when chemical components interact with light, heat, and various contaminants, causing oxidation, which reflects the new color. Yellowing caulk is a sign of failure, so choosing the right caulk and protecting it will extend its life.

In this article, I’ll explain the differences between caulks, why caulks turn yellow, and what you can do to prevent yellow caulk.

caulk turn yellow

Why Caulk Turns Yellow

The Adhesives and Sealants Industry wrote a very detailed explanation of the science behind why caulk turns yellow, but the main takeaway is that the discoloration effect itself comes from chromophores. 

Chromophores exist in some caulk chemicals, reflecting light their host molecules don’t absorb. This light hits our eyes in the visible spectrum as ‘yellow.’ Without any protective barrier applied to the caulk, it invariably becomes contaminated by light and the elements.   

Several newer caulks include yellowing protection as more companies have developed resistant sealants for specific applications. It’s important to know what application you’re using the caulk for and prepare it in advance.

Some surfaces must be primed before applying the caulk. Suppose you caulk onto a surface that isn’t sufficiently prepared to receive it. In that case, it will turn yellow before shrinking and cracking.  

Excessive Heat Exposure

Over time, caulk that is exposed to extreme outside temperatures or applied indoors near sources of heat risks degradation. Prolonged heat exposure causes the creation of free radicals that damage the caulk’s structure through oxidation. This damage is made visible through chromophores. 

Ultraviolet Radiation Absorption

Caulk is almost always applied to areas exposed to regular light. Specialty caulks developed for use outdoors and in wet environments withstand these effects much better than acrylic latex caulks made for indoor applications. 

caulks used on roof

When light interacts with the caulk, ultraviolet radiation is absorbed in the form of light photons. This absorption creates other free radicals that promote oxidation. 

Environmental Contaminants

Over time, exposure to various environmental contaminants threatens all paintable caulk, even siliconized versions. However, these will last much longer than non-siliconized caulks.

  • Dust and dirt contamination
  • Liquid and humidity interactions
  • Mold and mildew growth

Yellowing Caulk Care and Prevention

1. Remove Yellowing Caulk

While good options exist for removing yellowing from caulk (such as using bleach), the fact is that yellowing is a sign that degradation has already begun and the caulk is failing. If the caulk is failing, it needs to go because the reactions inside are continually taking place and won’t improve. 

remove yellowing caulk

The basic process involves:

  • Scraping off the entire strip of caulk 
  • Cleaning the substrate 
  • Laying down a fresh strip of caulk

Removing caulk takes time and patience, but not too much. This video by Ace Hardware shows you how:

2. Choose the Right Caulk

Selecting the proper caulk for the project sets the stage for maintaining its looks. There are three main types of indoor caulk:

  • Acrylic latex: Acrylic latex caulk is the easiest to paint. Still, it is the least flexible and water-resistant (its ability to clean up with water offers a clue). It’s a more affordable option, but more likely to become yellow. Due to its contaminant-collecting proclivities, acrylic latex must be painted.
  • Siliconized acrylic latex: The siliconized acrylic latex changes its structure to better fit the space. It expands and stretches while resisting cracks. It lasts longer than non-siliconized versions but can still turn yellow if unprotected. This option takes paint very well, so a couple of coats will protect for a long time.
  • Silicone: Silicone stretches and flexes well, making it an excellent sealant. However, silicone is notorious for its paint-rejecting properties, so it won’t work for areas that need paint. You can try priming and painting, but you’re better off using acrylic latex caulk with added silicone.

In addition to indoor caulks, there are outdoor caulks made from rubber or polyurethane that withstand the elements and accept paint.

3. Paint the Caulk

Once you have allowed the caulk to fully cure, lay down a primer coat before painting. Priming accomplishes several things:

  • Smooths over imperfections for a uniform surface. 
  • Fills the cracks between the caulk and adjacent surfaces.
  • Maximizes paint adhesion and improves paint-base versatility.

Using either oil- or water-based paint, paint the primed caulk according to the instructions. Paint improves caulk’s longevity and resistance to degradation because it blocks moisture and light.

If you’re redoing the caulk and need to redo adjacent painted sections, I wrote a guide on removing paint from wood, which you can read here.

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People Also Ask

Does Painter’s Caulk Yellow?

Painter’s caulk yellows over time because environmental contaminants interact with the caulk’s chemicals. There have also been instances where an ingredient in the caulk reacted with paint directly on it. 

Do Paintable Caulks Need To Be Primed?

Paintable caulks don’t need to be primed before painting. Still, the primer protects the caulk further from environmental hazards and potential interactions between the paint and the caulk’s ingredients.  

Does Decorators Caulk Go Yellow?

The decorator’s caulk will go yellow if left unpainted because it doesn’t contain the level of contaminant resistance of paint. Paint forms a protective barrier over the caulk, preventing chemical reactions due to various environmental factors that can turn it yellow.

Final Thoughts

Your best option for preventing yellow caulk is choosing the right caulk for the job and sealing it properly. But if you already have yellowing caulk, removing it immediately will prevent more damage to the area. Once you’ve prepped the adjoining surfaces, lay down some new caulk and seal it.

If you intend to paint, you’ll need a paintable caulk. Give it a coat of primer to maximize protection and quality. Painting the caulk once fully cured will protect it from the elements, which keeps it from turning yellow and failing.