top of page
  • Writer's pictureDave MacAusland

Why Does Wood Turn Grey?

Updated: Jan 6, 2022

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

Mold & Mildew

Wood, coming from being a tree, 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 watering a patch of dirt which then quickly grows plants, periodic wetting of wood, along with access to air, grows bacteria on the surface. When wet this layer of bacteria is dark gray. When the water dries, it turns light gray. Mold and mildew grow much more pronouncedly outdoors where frequent and prolonged moisture provides the water these bacteria need to thrive. Indoors wood tends not to get wet on a regular basis and hence doesn’t go gray from mold.

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". Breaking down wood's lignin causes the surface to develop microfine cracking, which deforms its otherwise smooth surface and results in light "diffracts" rather than being more integrously "reflected". This diffraction is a “blurring” event that makes the wood less colorful to the eye (kind of like a stainless steel mirror versus a glass one). Combined with the loss of visibility of the woods natural colorational pigmentation, the organic bacteria colonizing its surface, and the light diffraction from microfine surface cracking, adds up to your wood turning “Grey”.

So... Seal with Sun Frog and:

-Less microfine cracking of surface cells from UV

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

-More natural wood strength pigmentation PLUS color simulative Trans Oxides added!

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 does this).

  • Also, just as wood looks more colorful when wet with water, treating wood with oils (like with those of our Sealer) similarly improves its color coming to our eyes.

Is Turning Grey Bad For Wood?

Mold and Mildew don't harm the wood. However, allowing wood to absorb water frequently and deeply, thereby promoting wood rot fungus to grow, does! Grey is “old”. Colorful is “young”.

Maintaining your wood with an oil-based sealer (and ours contains a broad-spectrum EPA-approved biocide to inhibit surface growth of mold and mildew) diminishes deep water absorption, which prevents wood rot fungus from eating your wood, and also reduces checking (cracking of wood along the grain) which takes place over time by invasive wet/dry (swell/shrink) cycles.


Sealing your wood WITH SUN FROG SEALERS REDUCES water caused by wood rot, REDUCES surface caused greying and cracking, and AND REDUCES mold and mildew. It also beautifies your wood, keeping it looking young, not old! Not for use on HUMANS, UNFORTUNATELY!

133 views0 comments

Recent Posts

See All

Sun Frog got this inquiry today: Hello, I’ve got a IPE wood deck. What is your recommendation for a sealer? Thank You, Larry Here's how we responded: Larry- Because IPE wood cells don’t have hollow ce

bottom of page