Why Wood Turns Gray If You Use a Clear Finish

Effect of 18 Months of Sun Exposure on Bare Northern White Cedar
Effect of 18 Months of Sun Exposure on Bare Northern White Cedar-Image courtesy Perma-Chink Systems

 

 

“The bottom line is that if only clear coats are applied to exterior bare wood they provide only temporary protection against UV damage.” – Perma-Chink Systems

Our customers often ask us for a clear finish that will protect their wood.  The truth is, clear finishes may provide water repellency, resistance against mold and mildew and insecticidal properties, but clear finishes do not  protect your log home from damaging UV rays that cause graying of your home’s exterior walls, decks and rails.  With most clear finishes you will notice graying wood within 6-24  months of initial application.

Why will the exterior of your home turn gray if you only use a clear finish to protect it?   Clear finishes do not contain the appropriate pigment load to absorb UV rays from the sun. Clear finishes often contain little to no chemical UV inhibitors and the inhibitors they do contain are often “sacrificial, in other words the more UV light that they are exposed to, the quicker they get used up” according to Perma-Chink Systems. The result is a clear finish that breaks down rapidly from exposure to the sun, leaving wood unprotected and exposed to damaging  UV rays.  Wood will then start to turn gray, which is the natural reaction of bare wood fibers when exposed to the sun for extended periods of time.

We like to compare pigmented wood finishes to sunblock. Your body’s natural reaction when exposed to the sun over time is to tan or burn, it’s just how your body manages UV exposure. You apply sunblock to create a protective layer between you and the sun.  When you apply a wood finish that contains pigments or tints, you are accomplishing the same thing as you are with applying sunblock before you go to the pool, which is to provide a layer of pigment protection between the wood and the sun.

Semi-transparent, tinted wood finishes provide your wood with UV protection. Different wood finish brands contain various UV inhibitors, but the rule of thumb is the darker the tint of the stain, the better the UV protection for your house.  If your house is located in a high sun area, where it is fully exposed for hours at a time, LogFinish.com recommends using a finish with a medium to dark tint.

If your deck or wood exteriors are weathered and gray and you have decided to re-finish them with a tinted product it is important to first remove the gray, weathered surface. To do this, we recommend using a cleaning and brightening product that will leave your wood at the proper pH for staining as well as remove any dirt and pollen that has collected on the wood.  We do not recommend using household bleach and water to brighten wood because of its ability to dramatically change the natural pH of the wood. Instead, try out an oxalic acid based product like X-180 Weathered Wood Restorer, a wood cleaner and brightener for mild to severely discolored wood.

Thanks to the good folks at Perma-Chink Systems and LogFinish.com for inspiring this article and providing a wealth of information on this subject.