Wood absorbs water from the air during high humidity causing it to expand; during low humidity the water evaporates from it contracting it. After a project is finished this process is called movement in service. All species of lumber fall into one of four categories of movement: minute, little, average or great. The greatest amount of movement occurs across the grain {width.} Thickness has a lot less movement and the movement lengthwise is inconsequential. The thinner and more narrow the wood the less movement it will have. In fact wood that is less than 2 inches wide and 1/4 inch thick, the movement is minute or even inconsequential. Coating the wood with a finish will not stop the movement it just slows it down! The finish you choose to use, will determine how long it will take to reach EMC. For instance wood coated with marine spar varnish will take a lot longer than wood coated with tung oil to reach EMC.
The process of reaching {EMC} equilibrium moisture content to be in balance with the surrounding air {not gaining or losing moisture} is a slow process that eventually brings the piece in balance with its surrounding environment. There are a lot of variables that affect this process such as: whether your house is air conditioned with refrigerated air or evaporative {swamp cooler} or a combination of both. If it is heated with gas, electric heat or a fireplace, how well insulated it is and how {tight} losing air to the outside by way of cracks around windows, doors and other openings. If you use a humidifier or dehumidifier system and how much direct sunlight a room receives will also impact the movement of the wood. Even keeping the door closed to a room that has a seperate humidifier or dehumidifier will make a difference in the EMC of that room from the rest of house. All houses are different. In North America a lot of houses have an EMC of 6%-11%.
Wood that is kiln dried to between 6%-12% moisture content is extremely stable, 99.9% of wood defects such as bows, warps, shakes, twists, honeycomb checks and end splits are caused by improper kiln drying. Make sure that your wood is between 6% and 12% and does not contain one of the above-mentioned defects when you obtain it. This will decrease the problems that are caused by using improperly dried wood. If the wood is above 12 % do not use the wood for your project until it has reached acceptable moisture content.
Tip Of The Week
You can dry small pieces of wood in your gas or electric oven (WATCHING IT CAREFULLY.) DO NOT USE A MICROWAVE! In this day and age owning a good moisture meter is essential to assure that the wood does not have an extreme change after your project has been assembled possibly ruining a future heirloom and costing you a lot of wasted time and money. Another tip to remember is quartersawn lumber is more stable than plainsawn or riftsawn.
This Weeks Photo Credits go to C.T. Miltenberger Copyright 2003
This week I have some pictures that were provided by one of our readers, that I thought I would share with you. C.T. Miltenberger is a person who uses unique pieces of wood that he finds in his area to utilize in some of his sculptures.
The wood is Eastern Red Cedar also called Pencil Cedar. Botanical name is Juniperus Virginiana. It is in the classification of softwood {Conifer} and grows basically everywhere in North America from dry uplands, especially in limestone, to flood plains and some swamps. When worked {sawed, planed, sanded etc.} it gives off a sweet smell and if left unfinished this smell will emanate for years, because of this it is used for cedar closets, chests and for those cigar connoisseurs, who do not like the traditional smell of Spanish Cedar it is used in humidors. It is a light reddish brown to medium reddish brown with light to pale cream markings. The wood is fairly easy to work and has virtually no blunting effect on tools. Cutting tools should be sharp as this wood tears out easily. Some time back a disease killed many of the trees growing where C. T. Miltenberger lives in the Appalachian Mountains on the Maryland-West Virginia border so now there are dead trees sticking out along the rock outcroppings. Due to the windy and precarious places they grow, the trees are bent and twisted in all conceivable ways, creating magnificent and unique pieces.
Quote Or Proverb Of The Week
The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low, and achieving our mark
