Continuing with moisture and wood

I have met many woodworkers who feel temperature is a big factor in the movement of wood. I haven’t been able to find anything to support that idea. It has been proven that wood will not change in size or dimension unless the (MC) moister content changes. It’s important for you to have an idea of how the woods dimension and form will change in relation to the MC. Those facts become key elements in designing, assembling and especially warranting your product. My opinion is this, a " professional" woodworker, who is planning to invest hours of labor and money in a project, should consider the risk involved in not knowing the MC of the lumber. Not knowing is a bit like Russian Roulette. Later I’ll talk about measuring moisture in lumber.

Wood will change dimension the most across the face or across the grain of the board. There is very little movement along its length. You will notice a change on the thickness if the wood is exposed to high moisture conditions. You can really see this in a wood planked floor, especially if a latex finish is applied to it. With many floors you only have to look closely at the joint of the individual wood strips. If you see a uneven face, from one board to the next you can be pretty much assured latex finish was applied. I will give some insights on finish later.

Many different moisture content scenarios can develop with your lumber and or components. Lets start with the wood containing a too high MC right from the start. Assuming the wood is consistent in its MC, lets just use 10% MC. Unless your able to maintain a relative humidity of around 55% the wood you are using is going to give up moister and the net result will be shrinkage, again primarily across the grain. The wider the board \ component the more the net change in dimension. Sometimes a "even" loss of moister can be dealt with. The real problem comes when the wood or component gives up moister in an uneven ratio. A cabinet end panel or counter top for instance will give up moisture as the piece seeks to reach its EMC. Just imagine the dry winter air circulating freely over the out side exposed surfaces while the insides of the components have very little airflow over them. The exposed surfaces will dry and shrink at a rate different then its opposing side. This will result in cupping and warping. Either will normally ruin your day, not to mention your customers outlook.. And should you be working for your spouse, well you get the picture. In these scenarios it is my opinion that you as the cabinetmaker, would be at fault. You might be able to pass it on to your lumber supplier but your customer won’t really care at this point. Remember with this last point the reverse is true should you start with extremely dry wood and allow it to seek its EMC within a damp location.

Another factor to consider is that a woods end grain will absorb or give up, moisture approximately five times faster than the side grain. This results in splits on the ends of boards and panels.. Consider the panel of a raided panel door or possiblly a solid wood tabletop. Both have allot of end grain exposure. Consider our slightly damp wood with a MC of 10%, in a glued up panel which has begun the drying process. What would happen is this, the center of the panel would be stable compared to it’s MC at the time is was glued up, while the wood towards the end of the panel would now be shrinking across its grain as it gives up its moisture quicker the center.. If you could plot the stress on the panel it would look hourglass in its nature. If you’ve ever had a joint open completely and took the time to sight down it you can see the curve of each board as it is narrower towards the end and wider in the middle. With today’s glues the glue joint is usually stronger then the wood so its common you will see the split develop some where in the width of the board.

Hopefully I will draw this together more in the next post and give you some ideas of how to deal with some of the stresses moister causes.

moister and wood Continued

Continuing with the moister in your cabinets, with summer coming on the wood in your home will begin to adjust to what is normally a more humid time of year. There are a lot of variables to consider. The biggest being the location you live in. Here in Nebraska we have almost brutal swings in temperature and humidity. This constant fluctuation is about as hard on solid wood furniture as you can get. You can think of wood as a sponge. It is constantly seeking to equalize its moisture content with the moister content of the air surrounding it. There is actually a term to describe this, it’s called equilibrium moister content. Wood has a rather predictable response to the relative humidity of the atmosphere surrounding it. Assuming you maintained a 0% relative humidity (RH) in your home the wood in your home would eventually reach 0%, or its Equilibrium moister content (EMC), if the RH is 23% the wood would attain a EMC of around 5%, a RH of 48% would equal a EMC of around 9%., 60%RH would equal 11%. You may or may not know that most furniture grade lumber is considered dry and usable at 6 to 7% moisture content. Any time your wood exceeds that you’re heading for trouble. While the moisture properties are true for all woods remember we are talking about cabinet and furniture grade wood for the most part. In succeeding posts we will address more on how the wood responds to these changes and what you can do to make sure your cabinets and furniture remain stable and in good condition. Please feel free to post your thoughts, comments and such.

Humidity and your cabinets

For you trivia buffs. What was the name of the Knight who designed and build King Authors Round Table? (answer below)
Hey, it’s spring and if you’re like most people your thoughts are turning to home maintenance and fix up projects. One item I would put high on my "to do list" is sharpening the mower blades. Dull blades take their toll on your grass by shredding the cut edges rather than cutting them. This results in a brown to yellow cast in your yard and increases the water required to keep the grass healthy. Getting back to cabinets and wood in general, …that is the blog topic… summer humidity can be hard on your cabinets, especially the doors. If you have solid wood, raised panel, doors this is especially so.
Coming off the normally drier winter months makes this a good time to inspect your cabinets. Look closely to see if the panel in the center of your door has shrunk. Inspect it closely up both sides where the panel fits into the side pieces (called styles). You’re looking for unstained wood or dark lines on the panel. They will appear as the panel gives up its moisture, during the dry winter and shrinks. The line is where the panel was, in relationship to the rail, when it was stained and finished.
Movement is normal but problems can occur when to much expansion and contraction occurs. Usually the problem will be the unstained wood showing along the panel edge or a split in the panel. In another post I will go into more of the properties of wood and how to address the problem. For now you can be assured it’s one of two things, assuming you see shrinkage. The first is you need to add humidity during the winter months or the other being your finish may be not doing its job. There can be other tell tale sings your finish is failing which I will get into later. For now look at your doors next time your in the kitchen and see what you find.

Answer........Sir Cumference……

Welcome to the blog. Feel free to ask a question. If I can't answer it hopefully some one else can. Hopefully that's the spirit of the blog. I have learned allot by asking questions. I often ask my employs why questions about the projects they are working on, should they not be able to answer me I get real nervous.

A wise man once said..."The man who knows how will always have a job. The man who knows why will almost always be his or, hers boss".... That's a driving force in my life and one I hope that drives you as well.

I look forward to getting to know my fellow woodworkers and seekers of knowledge.