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Why Does Wood Turn Grey?

Updated: Jul 27, 2023

Wood grays from both bacteria growth on its surface (mold and mildew) and UV light damage to its exposed surface cell structure.

Mold & Mildew

Coming from being a tree, wood is an organic material. When a tree has been cut into boards and left outdoors, they are a food source for mold, mildew, and, ultimately, wood-rot fungus. While wood rot fungus thrives in dark, damp conditions (particularly below ground or with ground contact), mold and mildew can thrive in drier though still periodically wet, conditions. Like periodic watering of a dry a patch of dirt, mold bacteria quickly grows on wood surface that gets frequent moisture. When wet this layer of bacteria builds up, your wood will turn first light gray, then then progressively darker gray.

Sun Damage

UV light is an energetic wavelength from the sun (photon radiation). This energy breaks down the wood's lignin at its surface, the “glue that holds cells together". This causes the surface to develop microfine cracking, which deforms its otherwise smooth er surface and results in light scattering. This light scattering defracts rather than reflects the visuality of the wood to our eyes, thereby being a “blurring” event that makes the wood look different to our eyes (kind of like a looking into a stainless steel mirror versus a glass one). Combined with the loss of visibility of the woods natural colorational pigmentation, also from UV light degradation, UV exposure over time (6 months?) in part causes visual graying of your wood.

Taken together, the organic bacteria colonizing its surface, and the light diffraction from microfine surface cracking, this adds up to your wood turning “Grey”.

So... Seal with Sun Frog and you will get:

-Less microfine cracking of surface cells from UV

-Less Mold Growth (our Sealer incorporates a broad spectrum, EPA approved mildewcide), and

-Longer lasting natural wood pigmentation, and

- Our Natural Appearance, Color Additive, UV absorbing pigments in our colored Sealers ADD SIMULATIVE TRANSLUCENT COLOR TO YOUR WOOD.

Preserving Natural Wood Color

Can Graying be stopped and the wood be made to preserve its fresh-cut appearance?


  • Cleaning mold and mildew off the surface of the wood will allow the native color of natural wood to be seen by the eye (our Sun Frog Deck Cleaner followed by our Born Again Brightener does this).

  • Also, just as wood looks more colorful when wet with water, treating wood with oils (like with those of our Sealers) similarly improves its color coming to our eyes. And incorporating our non-vision impairing pigments helps add color when the natural color of fresh cut wood has weathered away.

Grey is “old”. Colorful is “young”.


Sealing your wood WITH SUN FROG SEALERS REDUCES beautifies your wood, keeping it looking young, not old! Not for use on HUMANS, UNFORTUNATELY!

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