Durability of Cedar Signs in Outdoor Exposures
Cedar should last 15 years in the weather — if the assembly details and finish are suitable. July 29, 2012
Question
We’ve been making hanging signs for local business for the last 2 years. Our city wants to hire us to make signs for their downtown locations. If we choose a western red cedar over engineered material, they are asking us what the longevity of cedar as a sign would be. In that we've only been into this for a short time, does anyone have an idea how long the cedar lasts outdoors? Assuming the wood is best left without a coating to try and protect it, what have you seen - 5 years, 10 years or more before the sign is replaced? Our signs are edge-glued with Titebond 3 and have biscuit inserts in between most of the stave work. We haven't tried kiln dried material for this yet, but have kept stock air dried before glue up. All is 2x6 material from local yards.
Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
Are the 2x6s treated? If you use WRC heartwood, the wood should last 15 years. However, the screws or hooks will probably fail, as there can be deterioration around the fastener and perhaps an entry way for water. A clear water repellant finish (non-film forming) renewed perhaps every five years would be great.
The biscuits you use are probably not needed, as they do not add strength to the joint. A spline or a mortise and tenon lengthwise would be really cool if you needed extra strength.
Stick with air dried material.
From contributor S:
Good to know kiln dried isn't needed. Would you recommend a clear non-film forming finish? So heartwood in cedar is based on the color, or how does one tell?
From Professor Gene Wengert, forum technical advisor:
Non-film forming, any color or clear, penetrating with excellent water repellency. Color defines heartwood. Some evidence indicates that second growth is not as durable as old growth.
From contributor M:
Old growth Western red cedar is hard to determine by color. It can range from beige, yellow, pink, brown and chocolate brown. Ring count and color can help. Be sure to use stainless fasteners, as they will resist corrosion. Old growth Alaskan yellow cedar is more weather resistant than Western red cedar but can cost more.
From the original questioner:
Can anyone tell me the drying schedule for WRC? We have kilns powered by sawdust fed boilers and have steam enhanced features on some of them as needed. We get the material locally and MC is around 15-18 at the most. If I'm right on this, we need to be around 10% MC for cedar. I know this would make a much better blade sign. Any thoughts on this?
From Professor Gene Wengert, forum technical advisor:
In much of the USA and Canada, 12 - 14% MC would be ideal. I do not know specifically for your city, but we can estimate it if you can give us the annual average RH. I think 15-18% is close enough as cedar is quite stable. You should ask for quartersawn, which also means very small shrinkage in width. Kiln schedules for WRC are in a book published by the US Forest Service, "Kiln Schedule for Commercial Woods."
