Expert: Greg Scholl - 9/19/2011

Question
QUESTION: I have read various answers pretaining to timber, not properly dried, but the cracking has occurred on various pieces made from different species of timber (all hardwoods)some more than a year old. All the pieces were fine until moved to a location where the air conditioning is on most of the time. Large cracks have occurred in tables and desk tops within a period of 4-5 months. One crack opened up with what could be described as a gunshot !!  Could it have something to do with the dry air and what can we do to prevent it?
Kind regards
Arthur Brown

ANSWER: Hi Arthur, it likely has a lot to do with the air conditioning, which as you probably know, is also dehumidifying. Are these new pieces, and was the wood properly dried?(8-10%)Or were they stored in one place, then moved into the new environment? It also makes a difference how the tops, and other large pieces, are fastened to the other structural members...as with all solid wood pieces, they must be designed and constructed in such a way as to allow for movement. Solid wood will always try,(and succeed) to equalize itself to it's environment, and any major changes...without being designed with the ability for the pieces to move, will cause damage,...sometimes with surprising and/or dramatic results. Also,if these are slabs of solid wood, containing the sap wood, pith, and other disparate grain, they are subject to multi directional instabilities while going through these changes.Certain species are also more dimensionally stable than others, but construction, design and using properly dried wood...as well as monitoring the humidity in all the various areas,(shop,storage, and final destination) are all important...

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QUESTION: Thanks Greg, In answer to your questions: were the pieces new etc, this is the position.
The majority of the pieces were new, however some were aound 10 months old and had been standing on showroom floor for that period before transporting to roughly 15 kilometres away as the crow flies. 2 of the large tables were manufactured from timber stacked under roof, for 6 years before use but fairly exposed to general outdoor hunidity. I am reasonably sure that the timber was stable with the humidity at point of manufacture, and though we have installed in the same area on numerous occasions this is a first! Could the installation of a humidifier,be a solution?   Kind regards Arthur Brown

Answer
"Reasonably sure" isn't a good way to be....especially when using solid wood that's been stored outside. You need to know the moisture content, using a pin type moisture meter or other means, and here in the northeast, we would likely still kiln dry that material before using it to make furniture..........and as I said...they need to be constructed in such a way as to allow for expansion and contraction, even with the appropriate moisture content.I would buy an inexpensive Hygrometer or two and place it in the space to monitor the relative humidity for a few days and see what it tells you, but it likely won't be practical to use a humidifier.If it's central air, some systems have the ability to rehumidify the air, but it's difficult to monitor or adjust unless someones willing to do that....you could also put a Hygrometer in the showroom where they were and see what it tells you as well....but to me it sounds more like this was a construction issue, using heavy solid wood timbers. However, without knowing any more it's difficult to be sure, of course. Here in the northeast U.S., we have a lot of homes heated in Winter with forced hot air systems, and this type of heat causes a lot of furniture damage, especially if the pieces are located near the vents.....it just has the capacity to really dry out things, and if not paid attention to, it can do a lot of damage....which helps keep us furniture restorers busy........I have a print out I give to many clients, and furnish to Antique stores to hand out,that explains the issue of relative humidity and what a Hygrometer is, and why one who collects fine furnishings should own and use at least one, and pay attention to it and adjust the relative humidity accordingly.....which can be a nuisance.