How to avoid climate caused problems with wood furniture and Kitchen Cabinet Doors

23 January, 2014 BY JIM HILL

New home Cabinet Doors and remodeled homes with Replacement Cabinet Doors can face a difficult environment if relative humidity is left uncontrolled. Here’s why.

Ideally the woodâ_Ts moisture content in Kitchen Cabinet Doors will be matched to the average relative humidity of the region where the wood product will be used. This will allow the woodâ_Ts moisture content to be stable. When the wood moisture content and the local climate is closely matched, the finish on the cabinet door will keep the moisture content in the door from reacting too rapidly to relative humidity changes and, therefore prevent the damage those humidity swings could cause to an unfinished door.

Wood with moisture content of 7% is said to be at equilibrium (that is it wonâ_Tt take-on or give-off moisture) when relative humidity is at 30%. So wood with a moisture content of 7% will be stable when the humidity is 30%. As the relative humidity increases above 30% wood at 7% moisture content will absorb moisture, increasing the woodâ_Ts moisture content. When relative humidity decreases below 30% wood at 7% moisture will give off moisture. Itâ_Ts not the gaining or losing of moisture that is potentially damaging to wood products, itâ_Ts the speed of the change in moisture content. Unfinished wood will see the end-grain change moisture levels at a much faster rate than the center of the wood piece, and wood with large differences in moisture content across the length will develop significant internal stress. This internal stress can result in catastrophic damages, like cupping, warping, and even serious splitting.

Humidity is seldom constant and changes in relative humidity are certain. Thatâ_Ts where the cabinet doors finish offers protection. The finish is not intended to completely protect the door from the effects of humidity changes. But it is designed to slow the changes to the woodâ_Ts moisture content with the humidity fluctuations. When a rain storm approaches the relative humidity will spike but the finish on the cabinet doors will slow that high humidity from being absorbed into your doors so quickly as to cause damage. Moisture will still enter the doors, but before the wood moisture content is significantly increased, the storm will have passed and relative humidity will have returned to a point closer to the regions average level.

A more serious condition exists when an unfinished wood product has acclimated to a humidity level above 70%. If wood which has stabilized at this relative humidity is subjected to a very dry climate, with relative humidity levels around 10-15%, the high moisture content in the wood will boil-off very quickly. This condition where moisture leaves the end-grain faster than the moisture leaves the center (to replace it) is typically the major cause on end-grain splits. While end-grain splits are not even abnormal in hardwood lumber, that same end-grain split in the panel-cut of your Raised Panel Cabinet Door would be a serious defect.

The door styles most likely to show splits are Raised Panel Cabinet Doors. The area most susceptible to damage from rapid moisture loss is the end-grain on the raised panels. These panel cuts are where the panels are machined down from the A_-inch thickness in the canter to A¼-inch thickness where the panel tongue fits into the groove machined into the Rails. Splits caused by rapid moisture loss are common in these panel end-grains. Splits in the A_-inch thick panel center are much less common.

All traditional cope & stick cabinet doors have exposed end-grain on the stile ends which can show splitting with rapid moisture loss, although not as likely as the raised panel end-grain.

Mitered doors have the stile end-grain slightly protected because of their design so stile end-grain splits are somewhat less likely than in traditional doors.

Itâ_Ts important to remember that we are talking about the worst-case of an Un-finished cabinet door being exposed to an extreme climate change. While this perfect-storm of events is likely to damage unfinished cabinet doors, there is a preventive solution; Finish your cabinet doors as soon as they are delivered!

As a rule of thumb, wood products manufactured in a damp climate and shipped into a dry climate, unless finished very soon after delivery, have a high degree of potential danger, while wood products made in a dry climate can usually be shipped into a wet climate (or any other climate) with minimal likelihood of damage. This is because most climate-caused damage to a cabinet door comes from rapid moisture loss, and damage from rapid moisture gain is far less likely. That is one of the mail reasons we built our factory in Arizona. Arizonaâ_Ts dry climate allows our products to be shipped anywhere in the country with very little risk of climate related damage to the product.

The sealer and lacquer will slow the moisture migration, even in extreme climate conditions, to a point where your new doors will be a dependable, reliable, and beautiful addition to your home for generations.

When considering a location to place your unfinished cabinet doors prior to finishing, ask yourself this question; would this be a place I would store an expensive piano or other piece of fine wood furniture? Click here to get Laura Ashley voucher codes for amazing furniture.

Accurate Sizing & Humidity Effects

Our cupboard doors are accurate to within 0.015 inchesThere are three key steps in manufacturing 5-piece Cabinet Doors that will determine the sizing accuracy of the finished door. If each of these steps is held within a tight tolerance, the finished product will be accurate to within the desired 1/64 inch, or about 15-thousandths.

The first of the three critical operations is moulder accuracy (sometimes americanized as “molder”).
The second critical operation is stile & rail length cutting accuracy and the third is consistency in stock removal during the operation of machining the outside edge.
Our standard is to hold each of the three critical operations to a tolerance of 5-thousandths of an inch. This produces a finished cabinet door with a worst-case sizing tolerance of 15-thousandths, of 1/64-inch.

The stile stock moulding operation starts the process of insuring sizing accuracy and, without close attention to this step, consistency in sizing the finished door is almost impossible.
When cabinet door stile stock is moulded, the width of this stock is the most critical factor in accurately sizing a 5-piece cabinet door. If the moulded width of the stile stock is held within a tolerance of 5-thousandths of an inch, the subsequent operations that affect sizing can be standardized.

At CabinetDoors.Com length cutting of stiles and rails is performed on CNC machinery so achieving our 5-thousandths tolerance for this operation is actually easy. Cutting accuracies of better than 5-thousandths are normal.
The outside edging operation is more difficult to hold because the edging cutter’s diameter changes from sharpening, so slight variations do occur. Our average edging tolerance does achieve the 5-thousandths inch goal, but the standard deviation shows a range from 2-thousandths to 9-thousandths inches.

Because the moulder accuracy is key to finished door sizing, let’s look at some examples of inaccurate moulder adjustment and the effects these errors will have on the finished size of a 5-piece cabinet door.
First let’s assume the moulder is set up correctly and the stile stock, which is targeted at 2 1/4–inch width, is actually oversized by 5-thousandths (2.255 inches). Assuming the rail length cutting and the edging operations are both perfect, the finished door will be 10-thousandths oversized. Most cabinet makers will be measuring the cabinet doors with a tape-measure, so the 10-thousandths error on this door will be considered perfect and within the acceptable range of even the most demanding cabinet professional.
Now let’s assume the moulding operation is not within a width tolerance of 5-thousandths and is actually over by 15-thousandths of an inch. That will make the stile width 2.265 inches, with the additional 15-thousandths doubled to 30-thousandths by the same error in each of the two stiles. This door will be oversized by 1/32 inch even if the other critical sizing operations are perfect.
This 1/32-inch error, while acceptable by the standards of the industry, is detectable with a tape measure.

The challenge to the cabinet door manufacturer is to size the door as accurately as possible by setting tight measurement quality tolerances on the operations that affect door sizing.

The variable beyond the control of the manufacturer is the normal swing in relative humidity and the effects humidity changes will have on the moisture content of the wood in the doors. All cabinet doors will react to changes in relative humidity by either absorbing, or giving-off moisture. Unfinished doors will react sooner to humidity changes, but even properly finished doors will eventually reach a balance between the relative humidity and the door’s internal moisture content. These moisture content variations will result in dimensional changes to the stiles and rails of the cabinet door.
These dimensional changes can be huge and are usually far greater than the total manufacturing sizing tolerances.
The definitive study on humidity and its effects on wood moisture content, and the changes it causes to wood dimensions was conducted by the US Forest Service, a department within the US Department of Agriculture.
The Forest Service, published the Wood Handbook: Wood as an Engineering Material in 1999 (and 2010), which outlined the expected moisture-content caused dimensional changes in various woods. The 1999 study focused on wood flooring but applies to all wood products kept inside the house and subjected to normal fluctuations in relative humidity. The 2010 study is extensive and covers almost all commercially used woods.
The 500+ page 2010 study can be viewed or downloaded here (Chapters 4 & 13 deal with Moisture and expansion properties)… http://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_id=100&header_id=p

I’ve tried to simplify the findings by focusing on plainsawn (Flat Sawn) Red Oak for this example. But, woods other than Red Oak and differing sawing-grain directions, like quarter-sawn, have different Coefficients for Dimensional Change. Because plainsawn woods are more popular and tend to have a greater dimensional reactions to moisture variations, I have used plainsawn in my example.
The bottom-line finding of the USDA research is that a 4% change in the moisture content of the 2 ¼-inch stile of a 5-piece Red Oak cabinet door will be expected to cause a dimensional change of 0.0332 inches, or about 1/32-inch, per stile. That means that a 4% change in moisture content is expected to expand, or shrink the width of a 5-piece Red Oak cabinet door by 1/16-inch, which dwarfs the 1/64-inch worst-case tolerance of the cabinet door as it finishes the manufacturing process.
This 1/16-inch moisture-caused change is 4-times the combined total tolerance of the critical steps in the making of a cabinet door, and certainly needs to be considered when designing cabinets. This is especially true when considering the spacing between butt-doors on cabinets. Without proper spacing, butt-doors may not close properly during high humidity periods.

These humidity-caused sizing swings may seem extreme, but keep in mind that these calculations reflect the humidity of the worst-case the country has to offer; the desert regions of the southwest. In the southwestern deserts relative humidity routinely changes from 5% in the dry month of June, to over 90% when the monsoon storms come in July. This wide humidity swing accounts for the 4%+ change in the moisture content of wood products in the southwest. Cabinet doors installed in other parts of the country will typically be expected to experience about half this dimensional change, or about 1/32-inch.

Design provisions to accommodate dimensional changes in the raised panels of cabinet doors are in place allowing the panels to float within the stiles and rails. The panels used in recessed panel doors are either Medium Density Fiberboard (MDF) or MDF core with wood veneers, which are dimensionally stable and react very little to humidity changes.

Looking at the once popular, and hopefully never to return to popularity, Slab Cabinet Door as an example , you can see the makings of a dimensional train-wreck. With the Slab Door we are not just dealing with the moisture-related dimensional properties of a 2 1/4-inch stile. We are now looking at the dimensional properties of a glued-up slab between 12 and 24 inches wide.
Using the same moisture-content calculations for plainsawn Red Oak from the Forest Service Study, we would expect to see a 12-inch wide slab door react to a 4% moisture content change with a width change of over 3/16-inch and a 24-inch slab changing width by over 5/16-inches.
Clearly width changes of these magnitudes are unacceptable and homeowners requesting slab doors need to be made fully aware of the dimensional instability of this cabinet door design.

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Moisture & Product Dependability

Humidity changes don't damage properly finished kitchen cabinet doors

Ideally the wood’s moisture content will be matched so the average relative humidity of the region where the wood product will be used will allow the wood’s moisture content to be stable. When the wood moisture content and the local climate is closely matched, the finish on the cabinet door will keep the moisture content in the door from reacting too rapidly to relative humidity changes and, therefore prevent the damage those humidity swings could cause to an unfinished door.

Wood with moisture content of 7% is said to be at equilibrium (that is it won’t take-on or give-off moisture) when relative humidity is at 30%. So wood with a moisture content of 7% will be stable when the humidity is 30%. As the relative humidity increases above 30% wood at 7% moisture content will absorb moisture, increasing the wood’s moisture content. When relative humidity decreases below 30% wood at 7% moisture will give off moisture. It’s not the gaining or losing of moisture that is potentially damaging to wood products, it’s the speed of the change in moisture content. Unfinished wood will see the end-grain change moisture levels at a much faster rate than the center of the wood piece, and wood with large differences in moisture content across the length will develop significant internal stress. This internal stress can result in catastrophic damages, like cupping, warping, and even serious splitting.

Humidity is seldom constant and changes in relative humidity are certain. That’s where the cabinet doors finish offers protection. The finish is not intended to completely protect the door from the effects of humidity changes. But it is designed to slow the changes to the wood’s moisture content with the humidity fluctuations. When a rain storm approaches the relative humidity will spike but the finish on the cabinet doors will slow that high humidity from being absorbed into your doors so quickly as to cause damage. Moisture will still enter the doors, but before the wood moisture content is significantly increased, the storm will have passed and relative humidity will have returned to a point closer to the regions average level.

A more serious condition exists when an unfinished wood product has acclimated to a humidity level above 70%. If wood which has stabilized at this relative humidity is subjected to a very dry climate, with relative humidity levels around 10-15%, the high moisture content in the wood will boil-off very quickly. This condition where moisture leaves the end-grain faster than the moisture leaves the center (to replace it) is typically the major cause on end-grain splits. While end-grain splits are not even abnormal in hardwood lumber, that same end-grain split in the panel-cut of your Raised Panel Cabinet Door would be a serious defect.

The door styles most likely to show splits are Raised Panel Cabinet Doors. The area most susceptible to damage from rapid moisture loss is the end-grain on the raised panels. These panel cuts are where the panels are machined down from the ¾-inch thickness in the canter to ¼-inch thickness where the panel tongue fits into the groove machined into the Rails. Splits caused by rapid moisture loss are common in these panel end-grains. Splits in the ¾-inch thick panel center are much less common.

All traditional cope & stick cabinet doors have exposed end-grain on the stile ends which can show splitting with rapid moisture loss, although not as likely as the raised panel end-grain.

Mitered doors have the stile end-grain slightly protected because of their design so stile end-grain splits are somewhat less likely than in traditional doors.

It’s important to remember that we are talking about the worst-case of an Un-finished cabinet door being exposed to an extreme climate change. While this perfect-storm of events is likely to damage unfinished cabinet doors, there is a preventive solution; Finish your cabinet doors as soon as they are delivered!

As a rule of thumb, wood products manufactured in a damp climate and shipped into a dry climate, unless finished very soon after delivery, have a high degree of potential danger, while wood products made in a dry climate can usually be shipped into a wet climate (or any other climate) with minimal likelihood of damage. This is because most climate-caused damage to a cabinet door comes from rapid moisture loss, and damage from rapid moisture gain is far less likely. That is one of the mail reasons we built our factory in Arizona. Arizona’s dry climate allows our products to be shipped anywhere in the country with very little risk of climate related damage to the product.

The sealer and lacquer will slow the moisture migration, even in extreme climate conditions, to a point where your new doors will be a dependable, reliable, and beautiful addition to your home for generations.

When considering a location to place your unfinished cabinet doors prior to finishing, ask yourself this question; would this be a place I would store an expensive piano or other piece of fine wood furniture?

Return to the CabinetDoor.Com/Blog.

Visit the Cabinetdoors.com website