When it comes to understanding the world of cedar, there are few people we trust more than “Mr. Cedar” himself, Paul Mackie. He’s been with the Western Red Cedar Lumber Association—known as the “voice of the cedar industry”—for more than two decades, working to represent quality cedar producers and educate others on all things cedar. In this series, he’ll share everything cedar-related, from what exactly western red cedar is to the difference between kiln- and air-dried lumber, to installation best practices.

Paul Mackie - Mr. Cedar - Western Red Cedar Lumber Association

Today’s video goes over the reasons western red cedar needs to be treated, how to stain western red cedar, and techniques to protect the wood throughout the process of treatment through installation.  

Why western red cedar needs to be treated

Western red cedar is a naturally durable product, and it contains water soluble extractives, sometimes called tannins. Tannins are tobacco-juice brown in color, and they’re found in the heartwood of the species. When tannins migrate to the surface, this is called “tannin bleed.” They’re brought to the surface by moisture. If you’ve followed our recommendations when it comes to prefinishing, then any bleed that occurs should only occur one time. Tannins are relatively easy to deal with. You can wash them off with soap and water.

Properly storing western red cedar before installation

Usually tannin bleed will occur with siding where the pre-finished siding has been improperly stored on the job site. We recommend that siding and trim be stored on the job site, on top of a vapor barrier, on top of “stickers”—two-by-fours or four-by-fours—loosely covered with the paper wrap in which the material was delivered. Lastly we recommend that that paper wrap be peaked, to allow for air circulation. If the western cedar is not properly stored on the job site, it can absorb moisture (even though it’s a kiln-dried product), and when it eventually gets installed, it can lose the moisture, bringing the tannins to the surface.

How to stain western red cedar

When it comes to solid-body finishes—paints and solid stain—for siding and trim boards, we recommend an alkyd oil stain blocking primer. It gets absorbed by the wood and then becomes a great base to which the topcoat of solid stain or paint will adhere. We recommend 100% acrylic latex topcoats, over an alkyd oil stain blocking primer. If you’re in an area where alkyd oil stain blocking primers are not available, you will still need a latex primer that contains stain blockers. These stain blockers help keep the tannins from migrating to the surface.

Common problems when treating western red cedar

One of the primary scenarios that we run into when we have failure of a film-forming finish—like solid stain and paint over primer—is improper surface preparation. This can happen if the wood is not pre-primed on all six sides before it is installed. The other thing that can lead to coating failure is installing the wood raw, leaving it exposed to the weather, and then attempting to field apply primer and solid stain, or primer and paint. This technique leads to adhesion problems, and the adhesion problems will be greater the longer the siding is left exposed to sunlight, rainfall, and dirt.

Another common problem is failure to prime the end cuts. Even if you’ve done everything else right, if you neglect to touch up the ends with the primer, that can lead to premature coating failure at that end cap, on the end grain.

How to protect treated western red cedar during installation 

Once you’ve treated the western cedar, it’s important not to undo the work in the installation process. If you overdrive the nails in installation, a pocket can be created, and the primer and top coat can be compromised. Overdriving a nail creates a hole where the raw wood is exposed. This hole will require putty, a dissimilar material to the wood itself. That’s why we recommend nails be driven flush, not countersunk. If you countersink them or overdrive them, you’ll have to take corrective action with putty or with a latex caulk. These changes will create a different appearance in the wood, and there will be spots in the areas where the nails were overdriven.

Stay tuned for more from Paul as we continue to learn from him on Dunn Solutions over the next few months, and catch up on his previous posts: