Weighting a slab question

consider your question

Bill Tindall, E.Tn.

I am wondering how much they will lose before they reach equilibrium?

How can anyone but you answer this question? The answer depends on the relative humidity of where they are reaching equilibrium and the moisture content they started with. The only way to know what they started with is to measure it.

I agree with Bill, but also

Keith Newton

There are variables, like the average green weight for the heartwood is 79, and the sapwood is 137%, so if you know how much the heart /sap ratio is, this may help.

However from a more practical standpoint, I would keep a close eye on it. If it starts to dry to fast on the surface before the core looses an equal amount, there will be small checks starting. Rather than hauling them outside, all you need to do, is cover them with canvas or plastic to cut off the drier air for a while.

I hope you did end-coat them.

Re: Weighting a slab question

Walter Ahlgrim

I would think over 50%

I weigh my ruff bowl blanks when they are dry. I do not bother weighing them for several weeks and I often see 25%

Fast drying is likely to crack the wood.

Walta

Re: Weighting a slab question

Larry Barrett

What you could do is cut off a small piece, weigh it, then put it in an oven at low temp, say 120 degrees. Continue weighing it until it stops losing weight. This might take a few days or so. At that point it will be near 0% moisture and the weight is called the oven-dry or kiln-dry weight. Then subtract this weight from the initial weight and divide by the oven-dry weight. Multiply the answer by 100 and this will tell you the initial moisture content of the slab, assuming that your small piece is representative of the whole. Knowing that, you can guesstimate what the slab weight will be when it reaches equilibrium wherever it will live.

drying

Bill Tindall, E.Tn.

drying for this test is done at 220 F and it will take about 2 hours. One dries until the dry weight does not change further. It is called "drying to constant weight".

Re: drying

Barry Irby

I was thinking that if I knew what the dry (target) weight should be per cubic foot or board foot I would have some idea how far I have to go.

I suppose I need to wax or paint the ends.

I was surprised that one of them weighed 90 lbs. If that were full saturation, what will it weigh when dry?

Trying to decipher what 8% means. 8% of what?

Re: Weighting a slab question

David Weaver

cellulose and lignin are both more dense than water, so if you can fill all of the space between them with water, you'd have a slab something greater than 95 pounds - theoretically maybe as heavy as about 115-120.

Dry weight on average for sweet gum is about 34-36 pounds per cubic foot (dry being 12% MC), suggesting an average slab of the size you're mentioning would be about 55 pounds fully dry.

the hunt for guitar wood reminds me just how far off some samples of various woods can be vs. those average densities, though (honduran mahogany seems to go from lightweight pine if it's young wood and not particularly good quality, all the way to WAY too heavy for guitars, like bordering heavier samples of cherry). No clue how much sweet gum varies - if it's like that, or if it's like red oak where it all seems to be in the same ballpark.

temperature for oven dry method

John K Jordan

>>>drying for this test is done at 220 F and it will take about 2 hours.

The Oven Dry method for determining absolute moisture can be betweeen 212 and 220F, ideally 217F. The time it takes to remove all moisture depends on the species, density, pore structure, and perhaps the phase of the moon.

>>>I was thinking that if I knew what the dry (target) weight should be per cubic foot or board foot I would have some idea how far I have to go.

Barry, you can look up the average density of any species but it is only an average. Specific pieces can be more or less dense.

Wood density chart *LINK*

Dick Coers

Here's a handy chart and info for you Barry.


https://www.nrs.fs.fed.us/pubs/rn/rn_nrs38.pdf

Re: drying

Keith Newton

Trying to decipher what 8% means. 8% of what?

8% of the dry weight.