06-09-2021: Wood Moisture

by | Jun 9, 2021 | Chips & Grits

Before starting discussion of the declared topic, one member talked about a YouTube video on how to make your own wipe-on poly. There were a variety of opinions on using a 1:1 ratio or 3:1 ratio of oil-based polyurethane and mineral spirits or another solvent. The ratio depends on how fast it’s needed to dry. One person in the video uses the 1:1 ratio for the first coat and the 3:1 ratio for subsequent coats on a large table top project. It was decided that woodturners probably won’t need to mix large quantities so the time spent mixing the liquids may not be worthwhile. A tin of wipe-on poly lasts a long time.

The discussion topic started with a question about what moisture content is best for woodturning. The AAW link to an article entitled “Wood: Kiln Dried, Green or Air Dried?” By Joshua Friend can be found at: https://www.woodturner.org/common/Uploaded%20files/WFPortal/Wood/WoodKilnDriedGreenAW2803p20-24.pdf The article says that most kiln dried wood has 6-9% moisture content. There are two types of moisture in wood: free moisture causes no problems (other than getting your smock and faceshield wet when you turn very wet green wood) but the bound moisture causes cracking as the wood dries.

One member’s home has 16-22% moisture in it. It was a higher amount than expected in our arid climate. No matter what moisture content is in the wood when it is turned, wood will react to the amount of moisture in the environment where the final object is stored by either losing or gaining moisture until it reaches equilibrium.

Some wood has been aging for 5 years with no problems while something only 6 months old has lots of splits. Cracks will happen and turners have to learn to work with them.

Measurement devices: Some members have moisture gauges with 2 prongs. Is it accurate? Different readings can be obtained from different places in the wood. Everyone was suspicious about the accuracy of the devices. There are scales for different woods, but are those really helpful? The gauge registers differently on end and on side grains perhaps because of the direction on the fibers. The density of the wood may make a difference also. One member suggested cutting off the end of the wood before and after taking a reading to see what the center moisture may be. Wood will be wetter inside and will take longer to dry. Perhaps the value of the moisture gauge is to watch moisture changes when working with green wood. It may have 30% moisture to start and 12% may be as dry as it gets. The key is to get the wood dry enough that the moisture level is consistent over time. The density plus the hard or soft nature of the wood affects moisture. The moisture meter gives a relative scale to watch drying over time.

A member asked if others put collection dates on their wood. Several people did but the dates are often obliterated by water or sun bleaching so have only occasionally been much help.

A rule of thumb for air drying wood is to allow one year per inch of thickness was described in this article: https://www.wood-database.com/wood-articles/drying-wood-at-home/  Unanswered questions by the group were: Does it apply to radial or longitudinal thicknesses? Could it apply to all species? Perhaps reading the article will help.

Can wood be too dry? Dryness can make it harder to turn and can result in more dust or powder. One member made cutting boards from the oak church pews that had been donated. He used mineral oil to cure but it soaked through due to going through the end grains.

How does boiling wood dry it? Members speculated that boiling may relieve the stresses in the wood and reduce the tendency for it to crack. It may normalize the cell moisture and help it dry equally. An AAW article by Ron Hampton that discusses drying by boiling, microwaving, and oven heating can be found at: https://www.woodturner.org/common/Uploaded%20files/WFPortal/Wood/DryingGreenBowlsAW1202p15-17.pdf

One member used a glycerin solution using Costco detergent and water to soak wood and make it easier to turn. He used a 5-gallon bucket, weighted down the piece and soaked it for 24-48 hours. The solution draws the moisture out. It makes it wet to turn but had less cracks later on. An article on this process originated by Ron Kent can be read at: https://www.woodcraft.com//blog_entries/soap-in-your-bowl. If you are an AAW member, you can also find an article under resources, articles, and search for “Soapy Bowls” by Ron Kent and Phil Wall.

Polyethylene glycol (PEG) and pentacryl are polymers that replace the moisture in wood and doesn’t shrink but isn’t always successful.

Wax or sealer on the ends of logs slow the drying process. (Reminder that the club sells a wood sealer for $24/gallon from either Gary Frank or Ken Allen.) If wax is impermeable, how does it help with drying? Radial and longitudinal shrinkage are different and the rate of evaporation on the inside is slower than the outside.

What can happen to green wood if a finish is put on it before it’s dry? It can blister, depending on the finish. Poly probably wouldn’t work, but an oil finish could work since it wouldn’t care about the moisture.

Green bowls could have a different shape after 6 months of drying depending on the type of wood.

Ways to dry green wood: Let it dry outside, or more slowly, inside. Microwave at a low power (in the shop) so it’s warm to the touch. Too hot is a problem. Use a smoker at a low even heat. (If you add chips, you could market it as seasoned wood or maple with hints of cherry or mesquite.) Make a garage kiln from an old refrigerator with an incandescent bulb as a heat source. Emiliano Archival of Hawaii uses one. There are articles in the AAW resource website called “Cool Kiln” by Bob Rosand and “Project: Kiln for Drying Wood” by Larry Zubke.

Speaking of AAW articles, there is one by Sara Robinson, “How to Dry Wood: A Beginner’s Guide,” that also has helpful information on our topic.

Drying wood is a form of dehydration, similar to drying fruit over time at a low temperature. We talked about freeze drying. It’s an expensive process that vacuums and freezes in a chamber at the same time.

A question: A member was turning rosewood and found it to be an oily wood that frequently clogs sandpaper. Some advice: use a slower speed while sanding, use abranet, wipe with denatured alcohol or acetone before sanding as a solvent for the surface oils. An oil finish was suggested. Lacquer wouldn’t work with an oily wood.

Different species of woods have different characteristics. Brazilian rosewood hadn’t seemed oily to one of our members. What determines if certain species are oily or not? Does the environment make a difference or the DNA of that tree species? Minerals in the soil affect the cells, but the way cells develop depend on that species’ characteristics. Woods evolve for survival reasons based on insect infestations and climate impacts. Trees develop ways to resist insects like beetles and during droughts create a tighter grain. (The only wood developing chainsaw resistance may be ironwood.) Fast growing trees in moist environments build their cells differently than those in drought conditions. In Phoenix, only succulents are natural; trees have been imported and have to adapt or die.

“The Hidden Life of Trees” by Peter Wohlleben was suggested as an interesting book on how trees change, communicate with each other, and protect themselves.

What is the difference between soft and hard maple? In one reference, soft maple is a common term for wood that’s not hard but hard maple is a specific species. In another reference, soft maple is 790 on the hardness scale, while hard maple is 1450, about twice as hard. Soft maple grows in a more temperate climate while hard maple grows in Northeastern North America. Pressing a fingernail into the wood may help tell if the wood is hard or soft. Or, look for the stamp on the wood “H” or “S.”

Surprisingly, box elder is a type of maple. Red flame box elder shows red due to its reaction to a bug infestation. One member had seen the bugs which look like fireflies with red rings on them but they do sting people too.

Are there helpful ways to get rid of sawdust? It helps absorb oil on a garage floor. It’s not good for putting it in a garden. Walnut is especially detrimental to other plants and keeps them from growing too close to it. Sawdust can help reduce the smell of dog poop. Craft Supply has an arrangement with local pet stores to clean up chips after their classes so the pet store can use the chips in the store.

Trees Native to Arizona

Per the Arizona Department of Forestry and Fire Management website at

https://dffm.az.gov/forestry-community-forestry/urban-community-forestry/tree-care 

Trees Native to Arizona (below 4,500 feet)

 Trees Native to Arizona (between 4,500 feet and 6,000 feet)

 Trees Native to Arizona (above 6,000 feet)