Lumber Grade and Verifying the Load Capacity of Railing Posts
In Question & Answer in the May/June 2011 issue, Andy Engel wrote on the subject of wood species and posts and referenced "4x4s in number 2 and better grades of common deck-building wood species." I am not trying to be critical but think that accuracy in such matters is important. The grade for 4x4s is "Standard & Better." "Number 2 & Better" is the designation for wider material.
It is important to make the distinction because lumber is tested differently for different typical end uses. If we do not all strive to use the correct terminology we risk losing the intended purpose and understanding. Our industry already suffers great distortion of communication regarding materials and their intended functions.
Bruce HoodPalmer Lumber Co.
What About Moisture Content When Staining?
In the July/August 2011 issue (Question & Answer), Andy Engel has reservations about waiting for the decking to dry out before staining. How does moisture content affect the life of the stain? I was always under the impression that it is very important to wait for optimal 12 percent moisture content in pressure-treated lumber. Does the moisture content vary with different species of wood, like cedar or ipe?
Steve StelkicDoylestown, Ohio
Andy Engel replies: Of course, if the wood is too wet, there's no room in its structure for stain, either water-based or solvent-based, to be absorbed. In that case, I'd expect early finish failure. So it is best to stain when the wood is at the optimal moisture content. But in my view, it's just not practical to sweat that out with a deck.
First, how do you know the wood has reached its optimal moisture content (MC)? The only way to tell for sure is to use a moisture meter. Readings taken from the surface of a board aren't accurate, as the MC usually varies throughout the board. Moisture readings should be taken from the center of the board using a pin-type meter, which means you have to cut the board in half. And you have to do that to several boards to get a representative sampling. Clearly, no one is going to go to that length. There are moisture meters that read from the board's surface, but I don't believe these are particularly accurate, as there are many variations in lumber other than the MC that can affect their results.And in fact, it isn't realistic to expect a board used outside to ever settle down to a uniform MC that's anything like 12 percent. MC's going to depend on the climate, and whether the board gets full sun, and how close to the ground it is, and whether the homeowner waters the lawn frequently.
Wood species won't make much difference, except that dense species like ipe will gain or lose moisture more slowly than less dense species like cedar. That's why my advice was to wait the stain manufacturer's recommended period of time, sand to remove UV-damaged wood, and stain according to the directions. And of course, you shouldn't stain right after or before rain. I did say to seal the end grain at installation, but the purpose of that is to slow moisture movement to minimize cracking.