Moisture Content, Humidity & Wood Finishes

If we read the information provided on this page for more details we can than agree wood carries a moisture content that when changing affects the size of the wood through expansion & contraction. Temperature along with the level of humidity in the environment where the wood is affects the wood differently depending on those variables. Too high or too low humidity along with warmer air cause the movement in the wood. Different wood species and different cuts of and/or thicknesses react differently. Harder or Denser woods like Maple & Oak move more than Softer woods. A  2" wide piece of Maple can shrink or expand by 1/16th of an inch. Veneers tend to move 1/10th of solid wood pieces & the wider a piece of wood the more movement that can take place.
Most Kitchen Cabinet Door Rails & Stiles are close to or at 2" in width which means as the wood acclimates to any given room it can shrink or expand 1/16th of an inch
This is a considerable amount of movement for just one style, there are 2 styles per door so a door can shrink 1/8 th of inch in it's width and height.

How does wood movement affect wood finishes?

Wood finishes are made to be flexible to some degree to accommodate movement of the wood. One key part of getting any finish to stick is starting with wood that has a lower Moisture Content or a stable content compared to your home.
45% Humidity at room temperature would be ideal for any given home, 60% is however not too high as long as it is constant. Moisture content in any given room when fluctuating greater than 10% whether up or down will cause movement in wood. The higher the swing in Moisture Content the greater wood will move.
Slight movements/slow movement of the wood are easier for finishes to hang on to, faster movement & constant variations or swings from low to high over 10% begin to cause problems for any finish.
An example of this would be a painted piece of wood left outside during the 4 seasons of the year. Sooner or later the swings in humidity & temperature cause hairline cracks not just in wood joints but in the finishes themselves, once this cracking starts it allows moisture to travel through the crack. Moisture then gets behind the finish and into the wood where sooner or later the finish flakes off or pops off the wood taking the primer & the paint with it.
This is exaggerated in the outdoors however the same conditions apply inside on wood surfaces just to a lesser degree.

When it comes to spraying bare wood or respraying over an existing finish the bare wood sprayed the first time will show more movement along the joints or seams and the overall width of rails & stiles. Older Kitchen Cabinet doors having a finish previously applied and acclimated to a home will move less, unless swings in humidity & temperature exist greater than the 10%
In a Kitchen environment moisture comes in two ways, Humidity level of the room & moisture from tap water near sinks or steam from kettles, coffee makers & boiling water.
Heat comes from home/exterior temperatures, ovens & boiling or steaming water.
All of these conditions to some degree can affect the wood & the finish.
Proper air flow like range venting systems, room fans and HVAC systems that circulate and remove the moisture from the air all reduce the likelihood that swings will take place in the moisture content of the room and also the wood & it's finish.
A poor working or not working range vent is bad and will begin to cause problems, air that is not circulating and removing humidity is also bad in a Kitchen. This is the same reason ceiling fans are required in bathrooms, to remove excess moisture.

This is all very important information as it directly relates to warranties whether from the door & cabinet manufacturer or the company applying a new or resprayed finish.
Wood movement can not be stopped, environmental conditions as described above directly affect wood & the finish's movement. Conditions in any given environment are well beyond the door manufacture or finishing companies control. These conditions vary from home to home and are under the control of the homeowner.
Spray It Like New Kitchens does NOT Warranty any sprayed items where wood movement causes damage of any kind including hairline cracks, cracking or flaking off of the finish where this movement causes these problems.
Our warranty is limited by species and condition or type of the material we are spraying or respraying to our workmanship which includes the following:
Dust particles, lint, bumps, runs, sags, uneven finishes or sheen level, tinted colour being off by more than 2% of a swatch or issues where the top coat did not stick to the primer or previous finish unless caused by grease , silicone or food debris.
Our process on new bare wood involves applying 2 coats of primer/sealer, sanding this down smooth, wiping dust down & applying 2-3 coats of the Titanium Based Acrylic Urethane.
Our process on previously existing finishes involves clean doors free of food and grease, finish sanding the old finish to remove the sheen, wiping with a mild solvent to further clean and soften the previous finish while opening up the pores of the old finish, applying the primer/sealer (the primer/sealer we use will stick to glass as long as the glass is clean), we then finish sand the primer/sealer, remove the dust & apply 2-3 coats of the Acrylic Urethane.
We make every effort to ensure the best bond possible & the smoothest finish possible for the material.
Despite every effort we make or every step we take humidity & movement of the wood will dictate how well and how long the finish will bond and remain looking good. Please ensure that you take every precaution to stabilize air flow, moisture & temperatures in your home to reduce the chance that the finish will deteriorate, crack and/or flake off prematurely.

How Wood Moves ~ Continued

If the MC of the wood you install is too high, excessive shrinkage may occur, along with the risk of problems of unacceptable gaps and cracks in the wood itself. When the MC is too low, the wood may expand, and may buckle, bow, and distort surrounding material.

There are six key areas finish carpenters should be aware of when it comes to wood movement.

1. Width of material

The wider the board, the more movement will occur (the term “board” technically refers to wood 1 1/2 in. thick or less, but for this article its use will refer to wood typically used by finish carpenters). It’s a direct proportion: an 8-in. board will move twice as much as a 4-in. board, and a 12-in. board will move 3 times the amount as a 4-in. board. And it’s important to keep in mind that a glued-up panel behaves basically as one wide piece of lumber.

2. Grain orientation matters

Boards are characterized as being either “flat sawn” or “quarter sawn.” Quarter sawn lumber (also referred to as “rift sawn” or “vertical grain”) shrinks and expands roughly half as much as flat sawn. Most over-the-counter finish material is flat sawn, and you should assume flat sawn values unless you’re sure your material is quarter sawn. Quarter sawn lumber has annular rings that are oriented between 45 and 90 degrees to the board’s face. Flat sawn grain orientation falls between 0 and 45 degrees to the board’s face.

3. Moisture content of the wood at delivery

The only way to accurately predict wood movement is to know the MC of the material when you receive it. Moisture content is measured using a moisture meter. Failure to check your delivered material means you have no chance of anticipating movement problems. Furthermore, material that measures outside of the acceptable MC level should be rejected.

4. Humidity inside and outside the structure

Homes in most of the U.S. that lack humidity control typically experience interior levels of humidity from 25% RH to 65% RH. This range of humidity will cause a 6% change in the MC of the wood. This change in MC will cause a 12-in. wide maple board to change 1/4 in.

When material is installed that was delivered at an unacceptable MC, or the humidity range in the structure exceeds typical values, the amount of wood movement increases—and can cause problems even in well-designed trim details. It’s worth noting that panel material (plywood, MDF, composite materials) move at about 1/10th the rate of solid wood.

In most of North America, exterior humidity levels range from 60% RH to 70% RH in summer and winter, but are lower in the Southwest, and higher near large bodies of water. If the material is delivered at 6 to 8% MC, it can experience more than a 2% change in size as it adjusts to the EMC.

5. Species affects the amount of movement

Wood movement depends in part on the species. A 12-in. wide western red cedar board will fluctuate 1/8 in. while the same size maple board will fluctuate 1/4 in. The formula for calculating wood movement is complex and extremely accurate, but tedious.

One simple rule of thumb serves as an approximate guide to predicting wood movement: “Most species of flat grain material will change size 1% for every 4% change in MC.” Applying this formula to a situation where the seasonal EMC ranges from 6% to 10%, a 12-in. wide board will change dimension 1/8 in.