Trained Eye

 
 
 

Treating Cedar Fencing

Question:

I will be building a new cedar fence, using pre-built tongue and groove 6 x 8 foot panels, shortly and I am not sure how to finish it. I want to preserve the natural cedar look and would prefer to have to treat it only every three to four years. Everybody I talk to has a different opinion about the best product to use on cedar.

Can you give me some guidance? Is it true I should leave it a year before putting any finish on it?

Thanks for your help.

Answer:

While inspection of fences is not often within the scope of a typical pre-purchase home inspection, the cost of replacement or installation of lengthy fences can easily be several thousand dollars. For this reason, it is essential that the materials are properly treated to get the maximum life out of the fencing.

There are two areas of consideration when discussing methods and materials for treating exterior wood components of a home, location and type of wood. While type of material being used appears to be the most important criteria, location and orientation of the wood is even more important. There may be completely different requirements for treatment of wood that is installed in a vertical plane as apposed to horizontally. Also, proximity to grade will also need to be taken into consideration when making your decision. Wood components that are in contact or in close proximity to the ground will be subject to “wicking” up of moisture from the soil or precipitation and are much more prone to rotting. This is of particular consideration in horizontal surfaces such as decks, especially those installed right on the ground. For your fencing, this is less of a concern as the fence is primarily vertical and most above grade, but other location considerations will apply.

The biggest enemy of all wooden exterior components is moisture. Wooden fences will be subject to numerous wettings, over their lifetime, from rains and snow and nearby vegetation. Trees and plants can severely affect a wooden fence’s ability to dry after wetting, which will promote moss and rot growth. For that reason, any sections of the fence that will be in contact with the ground, such as the bottom of the fence posts, should have below-grade preservative treatments in addition to any stains or finishes. Red Cedar has natural chemicals that help resist rot, but these will be limited in value if the wood remains constantly saturated

The second biggest detrimental environmental factor to exterior wood structures may come as a surprise. While exposure to the sun will have beneficial effects in quickly drying out wet fencing, Ultraviolet radiation will cause extensive discolouration to the cedar boards, if untreated. The greying of natural cedar is not due to moisture but UV exposure. For that reason, location of the fence in relation to other exterior components is important in your decision about treatment options. If the fence will be mostly shaded from the sun by buildings or large trees and bushes, a treatment with high preservative content and minimal colour may be a better choice than heavily pigmented stains. If the fence is to be built in a wide open area with no trees, plants or shrubbery, there will be less of a need for frequent reapplication of preservatives, but stains with more pigment may be required to prevent discolouration.

As you have pointed out, you will undoubtedly get numerous opinions on types of treatments for you new cedar but be cautious of claims by manufacturers of “clear” or “natural” treatments that maintain the natural, beautiful look of the new wood. Without pigments that contain strong UV protection, the wood will likely turn grey quicker than desired. To illustrate this point, think of the composition of sunscreens that we put on skin to resist sunburns. The higher the SPF rating, the more visible the lotion is when applied. As with many wood treatments, the heavier the pigment, the better the protection from the sun. The drawback of this property is that the pigments will often cover the natural look of the cedar which may be the main reason it was your choice of material, in the first place.

To answer your question about delaying treatment of the wood for a year, that is a bad idea if you want to maintain the original look. I am not sure where this recommendation originates from, but I have heard the same thing for many years and don’t understand the reasoning. Wood treatments and stains help seal in existing moisture in the wood, preventing warping and checking due to rapid drying. This can be seen on many untreated wood surfaces as the boards shrink and cup. If the boards are fairly dry when installed, treating as soon as possible after installation is desirable. If the fence boards are wet to the touch, as is often the case with newly cut cedar or boards left out in the rain, allowing several days to dry after erection of the fence is a good idea to ensure the treatment will be properly absorbed.

To try and summarize this often confusing subject, look for a cedar treatment product that has a good balance of UV protection, while maintaining the look of the original wood. Several manufacturers now have products that have moderate pigmentation that mimic the natural look of untreated red cedar, while having a high preservative component. These are often the best choice to avoid the need for yearly reapplication just to prevent excess greying of the wood. As with many building products, you get what you pay for and higher quality treatments are typically more costly as they contain more solids and less solvent.