Replies

1. 
   roqqytop | Feb 27, 2009 02:44am | #1

   Yes, get the dehumidifier and a indoor weather station.
   75% is too high.

2. 
   SgianDubh | Feb 27, 2009 04:48pm | #2

   Three paragraphs below starts some text lifted from some writing of mine on timber technology. It doesn't specifically address your question, but hopefully you will find some points of similarity described in that text with your own situation.

   To address your specific question, it may be beneficial for you to create stable conditions of RH in your timber storage and workshop area held at approximately 50% RH-- this equates to a moisture content of about 9% in most wood species, given time to reach EMC.

   If you can create those conditions reasonably inexpensively with a dehumidifier, or by any other means, eg, additional heat, then it won't hurt. I think the clue to the answer you are seeking can be found in your statement, "I am not really seeing any adverse wood movement so far... " In other words, the conditions in your wood storage and work area aren't causing significant problems to you; as long as that remains the case potentially expensive solutions involving technology, machinery, additional insulation, etc, seem unnecessary. Slainte.

   "An understanding of the relationship between wood, water vapour and atmospheric Relative Humidity enables a woodworker to develop strategies that suit local conditions. When I moved from the UK and lived and made furniture in Houston, Texas during my ten year sojourn there I had to adapt my previous working practices to suit my new working environment. To do this I learnt about and understood the local weather patterns and the conditions typically found in the habitable buildings of the area.

   Conditions on the American Gulf Coast where I lived are very different to my native cool and damp Great Britain. In Houston I worked in a typical all-expenses spared metal workshop with poor insulation and no climate control—during summer months it wasn’t unusual to experience 100ºF and, on particularly enervating days, 85- 97%RH. Although I didn’t keep records that provide accurate numbers, the combined thermometer and hygrometer on the workshop wall provided useful data on a daily basis. My Houston workshop generally had low and high RH percentages in the summer between about 95% (am) and 55% (pm). In winter equivalent figures were 90% (am) and 75% (pm).

   In America kiln dried native hardwoods such as cherry, maple and walnut are routinely dried to 7% MC in northern states, e.g., Pennsylvania. By the time I bought the wood in Houston’s hot and humid climate it had taken on moisture and was often 10%MC, and rising.

   Most, but not all of the furniture I made went to local clients and typical RH numbers in habitable buildings in Houston range between about 40% during winter and 60% in the summer—much the same as Great Britain, which is perhaps surprising.

   With careful thought and adapting what I knew of the relationship between air’s ambient humidity, wood moisture content, and its expansion and contraction I was able to satisfactorily make furniture for my clients. I knew that the wood in all the furniture I made during the year would almost certainly shrink at least a little in width once it was in a client’s house. As a consequence I had routines such as fabricating traditional hand-made drawers a little too tight for their openings. We did have an air conditioned office and completed pieces of furniture were put in it with the drawers removed. After a week or two in this environment the timber would shrink enough that a final fit of the drawers meant skimming off the top edge with a plane just prior to delivery.

   I also had to, and still have to take into account that some of the furniture I make could end up in unexpected places. Part of my furniture production is ‘on spec.’ It goes on exhibition in galleries and shows. At the time of building I have no idea where the piece might end up, nor precisely the range of relative humidity it might have to cope with in the future. I’ve always found it is prudent to design and make furniture to cope with quite an extreme range of RH, not a restrictive one. If the piece I’m building is a dining table or chest of drawers for a habitable building I try to allow for wood expansion and contraction that will occur between 5%MC and 15%MC. This equates to RH numbers of approximately 25% to 80%. These extremes are wider than I’d expect—but you just never know! Similarly a piece designed for a sheltered outdoor location under a porch or similar might have a change of use and become a garden piece or even sustained use in a conservatory. You can’t allow for every eventuality, but you can at least try to accommodate most circumstances."

   Richard Jones Furniture

   
   

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   Edited 2/28/2009 5:48 am by SgianDubh

1. 
   wolfonce | Feb 27, 2009 06:01pm | #3

   Thank you Richard. That makes the job easier. It does make it more complicated but knowing all the parameters makes the job easier. Dave