End Cracking of Round Posts

1. My mailbox from the road.
2. The top of my mailbox post

My Mailbox

My mailbox has been hit by passing cars several times in the past few years.  The last one was a good one so it was time to get a new mailbox.  The new post is pressure treated for ground contact with ACQ (alkaline copper quaternary) and was set in concrete to be sturdier.  I was concerned about having a flat exposed surface so I cut it so that water cannot sit on the top surface of the post.  I did not field treat the post because there was complete penetration of the preservative so I felt that field treatment was not necessary.  I did not determine the moisture content of the post at the time of instillation, but it was dry to the touch, and I proceeded with the assumption that the post had been kiln dried to approximately 19% moisture content.  After about one year of service, the exposed end of the post is severely cracked. 

Wood Shrinkage

An annual application of a water repellent would have helped but this situation was probably inevitable for two reasons.  The first reason is due to anisotropic shrinkage.  This is a fancy way of saying wood shrinks, and swells, at different amounts depending on the grain direction.   For example, in a flat sawn board, the thickness is the radial direction and the width is the tangential direction.  The opposite is true in a quarter sawn board.  The tangential shrinkage is typically twice that of the radial shrinkage.  This is the reason you often see cracks on the end of a log that resemble spokes in a bicycle wheel.  As the wood is drying, internal stresses develop and a crack develops when the stress is greater than the inherent strength of the wood.   My mailbox post has been exposed to several cycles of hot and cold, wet and dry which leads to swelling and shrinkage.  This repeated cycle inevitably will cause checking, particularly in round stock (posts and poles). 

Polyethylene Glycol

In my opinion, the most effective solution and mostly widely used is to use a wood stabilized such as polyethylene glycol (PEG).   The PEG solution penetrates the wood and keeps the wood at the same moisture content and stops the cyclical shrinkage and swelling cycle that causes cracks.  It works by “bulking” the cell wall.   This prevents the cell wall from gaining or losing water molecules.  If we can control the gain and release of water molecules in the cell wall, we can control the dimensional stability (i.e., shrinkage and swelling) of any wood member.   PEG is expensive and the resulting wood surface may not accept the finish of your choice. It also takes extra time to apply and may require additional equipment to make it work correctly.  However, PEG is very safe to use and is non-toxic to humans and the environment.  It has a long history of use by wood workers that need to stabilize wood for making items such as duck calls, wooden eggs, bowls, etc.

Todd Shupe is the President of DrToddShupe.com and is a well recognized expert on wood-based housing and wood science.  Shupe worked as a  professor and lab director at LSU for 18 years and Quality Manager for Eco Environmental (Louisville, KY) for 2 years. He is active in several ministries including his Christian blog ToddShupe.com. Todd is the Secretary of the Baton Rouge District of United Methodist Men, Database Coordinator for Gulf South Men, and volunteer for the Walk to Emmaus, Grace Camp, Iron Sharpens Iron, Open Air Ministries, HOPE Ministries food pantry. Todd is currently preparing to be a Men’s Ministry Specialist through the General Commission of United Methodist Men.

Maintaining Your Wood Cutting Board and Knives

Wooden cutting boards and knives are my most used kitchen tools.  Obviously, as for myself, we use all-natural wood and not polypropylene or polyethylene (plastics) cutting boards.  I don’t buy organic food but I try to avoid products produced from natural gas, feedstocks derived from natural gas processing, and feedstocks derived from crude oil refining (i.e., plastics).

Wood or Plastic?

Wood because it’s the best choice for maintaining a knife edge and wood cutting boards and knives simply look nice.   Most chefs will tell you that they find most plastic boards quite ugly, especially over time as they stain and get roughed up. Eventually plastic boards need to be discarded, whereas I’ve had some of my wooden cutting boards for over 30 years.  Wood cutting boards and knives need about 5 minutes of love each month.  There are many options for maintaining your wooden kitchen items, but I use a mixture of mineral oil and beeswax.

Process

Wooden cutting boards need to be kept clean and the best maintenance is washing with hot soapy water after using.  Do not clean wooden kitchen items in your dishwasher.  This will dry them out and cause cracking.  Initially, the cracking may not be visible to the naked eye but rest assured it is there.  You should never soak your boards or knives in water.  You run the risk of cracking because the moisture content of the wood is increasing quickly while uner water and then decreasing quickly as it is removed.  To sterilize your wooden kitchen items, you can use a very diluted bleach solution or hydrogen peroxide to clean their boards after they’ve been used for cutting raw meat as a precaution against bacterial contamination.  

You should oil wood cutting boards and spoons to help maintain their surface and keep them from cracking. I try to do this monthly.   You may need to do it more or less often.  You have many choices to use for oil.  Whatever oil you use must be food grade and not prone to rancidity.  Mineral oil is an inexpensive and popular choice, and is readily available.  The boards must be clean and dry before oiling.  The oil should be rubbed on with a clean cloth or paper towel and allowed to soak in as long as possible.   A good practice is to apply the oil in the evening after cleaning up from dinner, and then gently wipe off any excess oil on the surface the next morning.   If the wood has an unpleasant odor, apply a small amount of beeswax or lemon oil to the oil.

You should oil wood cutting boards and spoons to help maintain their surface and keep them from cracking. I try to do this monthly.   You may need to do it more or less often.  You have many choices to use for oil.  Whatever oil you use must be food grade and not prone to rancidity.  Mineral oil is an inexpensive and popular choice, and is readily available.  The boards must be clean and dry before oiling.  The oil should be rubbed on with a clean cloth or paper towel and allowed to soak in as long as possible.   A good practice is to apply the oil in the evening after cleaning up from dinner, and then gently wipe off any excess oil on the surface the next morning.   If the wood has an unpleasant odor, apply a small amount of beeswax or lemon oil to the oil.

Theory

Wood is a hygroscopic material, which is just a fancy way of saying that it will gain and lose water depending on the ambient conditions.  Wood is also an anisotropic material, which again is a fancy way of saying its properties, in this case shrinkage and swelling, are different in the different directions (width, thickness, and length).    Changes in wood moisture content between 0-30 percent will result in either shrinkage or swelling.  Changes above 30 percent will not affect the dimensional properties of wood.   Wood will swell or crack as a result of rapid changes in moisture content.  Food grade oil will coat the surface.  The purpose of the oil is to penetrate the wood and saturate the wood fibers to stop any other liquids (water, blood, etc.) from soaking into the board. A well-oiled cutting board 

or knife will keep the same shape when the wood fibers are saturated, so it will not expand and shrink and therefore will not crack or warp.

Todd Shupe is the President of DrToddShupe.com and is a well recognized expert on wood-based housing and wood science.  Shupe worked as a  professor and lab director at LSU for 18 years and Quality Manager for Eco Environmental (Louisville, KY) for 2 years. He is active in several ministries including his Christian blog ToddShupe.com. Todd is the Secretary of the Baton Rouge District of United Methodist Men, Database Coordinator for Gulf South Men, and volunteer for the Walk to Emmaus, Grace Camp, Iron Sharpens Iron, Open Air Ministries, HOPE Ministries food pantry. Todd is currently preparing to be a Men’s Ministry Specialist through the General Commission of United Methodist Men.