Question (WOODWEB Member) :
Does anyone have a policy to deal with shrinkage in their furniture after a customer places it into service?
(Furniture Making Forum)
From contributor M:
I state clearly that my warranty is void if the woodwork is damaged as a result of exposure to excess humidity or moisture. I define this as greater than 55%, or below 25%, which is still generous in my claimant. I also state that the more stable the environment is the better, and that changes in dimension are to be expected. In my care statement I warn against storage in garages, basements, attics etc. I also mention that fine furniture should not be placed over, or directly adjacent to a heat register, or other heat source.
I generally dehumidify my shop to about 45% when conditions get above 48% RH in the summer. This year I am going to get an air conditioner. I can't work when I am dripping sweat all over finished surfaces. If the humidity in my clientís home is greater than my shop by more than 5% I try to match it a bit closer. I have to constantly educate my customers on this. I get asked to build stuff that would self-destruct, and then they second guess you when you say you canít do it their way. It would be nice if all of our customers had archival quality climate control in their homes, but that is just not realistic. I am glad to cover warranty issues that are clearly my fault, for example problems from using wood with a high MC, or from improper construction. However I go to great lengths to prevent this. Beyond that I can't be responsible for what nature does to itself, provided I did everything I needed to do.
As we all know, wood will shrink or expand as it will. All we woodworkers can do is to try to mitigate or buffer (or hide) this fact. It all starts with the design, compounded by the process.
My shop was totally un-conditioned, except for spot heating and cooling. As a test, I glued up an 18" wide piece of oak. Over a two year period, its minimum and maximum widths changed by 3/8". So, from a design perspective, if I were to insert an 18" wide board into an 18" wide mortise, there would be a substantial amount of stress points created very quickly, and the piece soon would be destroyed or damaged. As a remedy, one would create two (or more) narrower mortise and tenon joints to lessen those stresses. Another remedy would be to use a different wood. A piece of mesquite under the same conditions moved an almost indiscernible amount.
A properly applied film finish will slow down the wood movement. As relative humidity goes up or down, so too will the wood's moisture content, albeit at a much slower rate because of the additional vapor barrier of the finish, thus minimizing the actual change in the wood's dimensions. By the way, wax is not a finish.
A properly made raised panel door actually allows for wood movement, but the end result can eventually be unsatisfactory because the staining/ finishing process was incorrectly accomplished. Many shops assemble the door, then stain and finish. When that panel shrinks, the unstained edges show.
Molding and trim were invented to hide gaps. It's all about reducing or accommodating the inevitable stresses. Making a well-thought-out bookcase in Arizona and shipping it to New England should be less of a problem than, say, a parquet tabletop. With the bookcase, all of the movement is in a parallel direction and a nominally equal amount, so everything moves as a unit. With the table, the movement is in all different directions, thus offering no stress relief.
How a customer takes care of the furniture is a factor of course. If the owner is constantly moving the furniture piece into the garage for storage and then back into the house, that piece is going to suffer.
An informational packet, discussing the customer's responsibilities in caring for the furniture, goes a long way in preventing future issues.
If a piece of furniture shows wood movement problems in less than 10 years, it is either from poor design, poor workmanship, or customer/ elements abuse. 10-20 years, you may want to help the customer if you can. Over 20 years, hey, that's wood! (These numbers are highly subjective.)
If the problem is of your making, own up to it. The cost of materials and labor usually is far less than the cost of a tarnished reputation.
For woodworkers and many "civilians", solid wood furniture imparts a sense of beauty that few other items match. Making solid wood furniture imparts a sense of satisfaction that only a few other activities match.
In the summertime, the average inside a home or office is 50% RH or 9% EMC. (If a home or office gets much more humid, we have paper feed problems, mold in bathrooms, dampness here and there, etc. Air conditioners generally remove moisture and the low RH helps us feel cooler even when temperatures are a bit high.)
Some manufacturers are told two humidify their shops in the wintertime to get 40% RH or higher. This does help prevent lumber problems during manufacturing if the lumber is not dried to a low enough MC, but it also postpones shrinkage problems until the homeowner gets the item. Run the shop at the same RH (or a bit drier) that the homeowner has.
A homeowner has the right to expect that in the normal dryness of his/her home or office in the wintertime that the furniture will not shrink excessively after it was made. One thing that will help you prove that your items are properly made is if you measure their MC with a moisture meter (made in the USA) that costs at least $250, and of course your readings were all around 7% MC and not wetter. On the other hand, if you ship to Denver, the RH can be very dry at any time. If you ship to the Florida coast, the reverse.
As indicated, garages can be 12% EMC; basements 15% EMC, and unheated home under construction, 16% or so. Servicing these markets seems to require that the furniture or cabinet is put in a plastic bag, which (if no holes) will hold the moisture constant for years. Note that outside conditions in almost the entire USA average 65% RH or 12% EMC, summer and winter. Our bodies do not judge humidity very well. When it is 45% RH and 95 F, we think it is hot and humid, but the wood only sees the 8% EMC. Temperature is not an issue. Coastal areas are more humid and higher elevations in the West are drier.
I have several clients that have an old 18-wheeler trailer that is without holes. They store any incoming wood in it and keep the RH under control by heating the inside until they get 30-35% RH (about 25 F above the morning's low temperature) all year round. One client went from over 100 complaints in a year to just three. Another reduces warping issues in their product from 23% to 6%. For about $30, you can get a reasonably good and accurate (as accurate as we need it) digital RH sensor. With this (or several) you will know what is actually happening in storage, manufacturing, shipping, customer's home, etc.