Red oak, relative humidity and moisture content

[Scott]

Just picked up enough red oak to make a couple small tables. I have

5/4 & 6/4 planks (the 6/4 is quartersawn for the table top), and a chunk of 12/4 for the legs. This wood came from a local hardwood supplier that stores their wood stacked but unstickered in a metal shed (unheated, it seems). My garage is at 43% RH tonight. When I put my hygrometer inbetween the now stickered boards, it reads 50% RH.

Question: is it safe to assume that I can use this wood when the RH right up snug against the wood is the same as the garage? I'll probably do the weigh and bake moisture test tomorrow, but I am curious about the RH idea ....

Thanks,

Scott

[Tom Watson]

When it is safe to use the wood involves a reciprocity between the moisture content of the wood and the stability of the environment that it will live in.

The moisture content of the wood is best measured by a meter that is designed for such use and it is generally agreed that the moisture content should be about 6%.

The reason that it is called out at 6% is that this is the moisture content that will best survive in a controlled environment that is about 68 to 72 degrees and has a relative humidity of about fifty percent.

There are places in both England and the US that might not have central heating or summer air conditioning and this would make the 6% measurement almost worthless.

The real game is about the equilibrium moisture content for the piece in relationship to the environment that it will live in.

If you make a piece with stuff that's living at the 6% level and put it in a home in Florida that does not use air conditioning, that would be a bad thing.

Find out what the general conditions of the space is that the piece will live in and then build your piece with stock that is tempered accordingly.

Thomas J. Watson-Cabinetmaker (ret) Real Email is: tjwatson1ATcomcastDOTnet Website:

[George]

What Tom means to say is consult the tables, where 50% RH equates to an EMC of 8-9%, which is the standard to which wood is kilned where I live and where I've been.

Once the wood leaves the storage area (we used 45%RH at school) it adjusts to the ambient conditions. Knowing this, a woodworker allows for movement in his projects. That's why panels are framed and floated, and tabletops merely held down, not fixed. Finishes slow the effects of rapid RH change by slowing uptake and release of moisture in the wood, which is why we apply finishes to both sides.

Build tight in high humidity, loose in low, but smart in all. Look to your design, and try a book like Hoadley's _Understanding Wood_ for the proper guidance.

Neat stuff here, too

[Scott]

Hi Tom, and thanks for the reply.

Funny how many guys will buy a classical guitar made insome coastal village in Spain, and have it shipped to the desert West . . . and watch that expensive Brazilian Rosewood form nice cracks . . .

The mean annual RH in my home one year was 42 percent; this is now the RH I maintain when I glue a guitar together. The wood I use for guitars has been stored locally for years, and is thus ready to work with. The oak I picked up yesterday ... I don't know it's history. I think I'll call the supplier today, and learn more about their stash, and perhaps see if they can give me a moisture content reading (since I lack a meter of myown at this time). Also, I see Hoadley has a nice map showing ideal moisture contents for the USA; for Idaho it looks like your 6% figure is right on.

Cheers,

Scott

[Scott]

Called the hardwood retailer to ask about MC: he said they bring the wood into the shop at 6-8% MC, where it sits and equilibrates to the local climate until someone buys it. Since I live in the local environment, he said that I should feel free to begin building. Scott