White stain under epoxy coating

Interesting.....

Barry Irby

Can't contribute much but questions....

I think what your friend has is a "cookie".

If it is six inches thick and was air dried, I doubt it is completely dry. It will never be completely dry, but I am saying I doubt it has reached equilibrium. The one inch per year rule (which is not a rule anyway) does not apply because this piece is all end grain.

Most cookies crack and end up looking like someone took out a thin slice of pie.

You did not mention whether he coated the bottom side. Usually a good idea to treat both side equally. If he did not, it will continue to dry to the bottom and may warp and crack. Not sure what will happen if he coated both sides and it's still green.

With this much end grain and such short fiber length it may have dried more than a typical board. A shame he did not weight it before and after. OTOH, if that is a five foot diameter cookie and it's five or six inches thick, that is one heavy table top.

I am curious about this. I have a giant red oak tree that has been slabbed and is stacked and stickered in a shed, drying. Been drying about six months. At about a year I will try getting one or two slabs kiln dried. Maybe. Keep us posted on your friend's progress. I have actually heard one crack and I fear he may too.

Re: Interesting.....

Pete in Holland MI

Hi Barry -

Yea, he is more of a dreamer than a true wood worker, but if it does hold together, it is a stunning table. Cookie? Perfect name. The pedestal is a square cut about 24" square. Yes, it IS a heavy table. Doesn't move much when you slam your leg into it (experience talking).

Just curious about the white stain in the epoxy, if that is damaged epoxy, or a reaction to the wood underneith, and if it will reduce in time.

Thanx !

Impossible for moisture to migrate through epoxy

Dick Coers

Just an assumption, I've never done any scientific studies. If it could, a lot of fiberglas boats would be in trouble. Is there any finish on the bottom?

doomed to failure

Bill Tindall, E.Tn.

Why:

the tangential shrinkage of oak is 8% and the radial 4% (approx. to make the calculation easy to follow).

what do these values mean? They mean the circumference of the disk will shrink twice as much as the diameter as the wood dries. The circumference can't shrink twice as much so it will open cracks to be able to shrink this amount as illustrated in the picture of a pine disk.



As stated this disk of wood had a diameter of 5', and hence a circumference of 15' (C=piD). When dry the diameter will shrink 0.04 times 5 or 0.2 feet. To match this shrinkage the circumference would need to shrink 0.04 times 15 feet equal 0.6 feet. If the diameter and circumference both shrank 4% the disk would not split. But, the circumference in fact shrinks twice as much. When the diameter shrinks 4% the circumference will have shrunk not 0.6, feet but 1.2 feet. A crack, or cracks, of 0.6' will open up around the circumference to relieve the stress.

I have no idea what makes the white but it likely has something to do with water making bubbles or crazes in the epoxy.

PS that pine disk was cut in 6 seconds with a cross cut saw in a competition.

nit picking

Bill Tindall, E.Tn.

Actually water molecules migrate through all plastics, but as you know, not very fast. Water is a tiny molecule and plastic (polymers) have lots of molecule sized vacant space in them. Sealed in a thick layer of epoxy it could take decades for that oak chunk to dry..... and crack. It will be interesting to see what sort of chemistry goes on in the soggy wood sealed in the epoxy shell.

At 67, decades means impossible for me

Dick Coers

My Mom lived to be 87, but her brain was gone years before that. My Dad was 61. I don't think in decades any longer for me.

agree

Bill Tindall, E.Tn.

but I nit picked because the diffusion of stuff through seemingly "solid" plastic explains some things not obvious. Some may be curious. You won't see beer in plastic except for short term storage(oxygen). After a few years a gallon of Titebond will be thicker(water). Soda in a plastic bottle will be flat after a year of storage(carbon dioxide).

Re: doomed to failure

Don Stephan

And a much cleaner cut than a chain saw!

water through plastic

John K Jordan

>>>...the diffusion of stuff through seemingly "solid" plastic explains some things not obvious.

I read that CA glue will set up in a typical plastic container due to water vapor entering the bottle through the plastic. The possibility of condensation from moist air entering the bottle is the reason it is recommended to let a bottle stored in the fridge or freezer come to room temperature before opening.

Mercury Adhesives claim their bottles are specially formulated to resist the water vapor. In any event, they offer a lifetime replacement warranty for failed containers of CA, no questions asked.

I keep water vapor away from my CA by storing in a sealed container with indicator desiccant. Works well. I recharge the desiccant when it starts to turn pink.

JKJ

I've been wondering for a long time,

Keith Newton

Wouldn't the tangental / radial relationship need to be pi to prevent the radial checking? Well, that would be taking away the quicker drying factor for the sapwood v heartwood relationship.

Oh, and for anyone wanting to use these cross-cut sections, I would suggest that if you cut them diagonally rather than straight across, this gives these stresses a way out, by going from one face diagonally across and out the other face.

At 67, decades means impossible for me

Tom Colligan

Keep pedaling that Ferrari of a bicycle you have, Dick, and you will likely get pretty close to 87.

Tom

The Villages, FL

Thanks Tom

Dick Coers

That’s two of my reasons for riding. Mind and body. Planning on the eBike being a time machine.

geometry

Bill Tindall, E.Tn.

Your question hinges on whether we speak of shrinkage as an amount or a percentage. As an amount, yes C must shrink pi times something. But as a percentage pi is not a factor.

C = piD There is a linear relationship between these factors when it comes to shrinkage. If D shrinks 10% and C shrinks 10%, C still equals piD, that is to say, the circumference shrank exactly enough to accommodate the shrinkage of the diameter..... 0.9C = 0.9Dpi

If they don't shrink the same, 5 and 10%.....

0.9D =/= 0.95C C must open a crack of 0.05%D to remain stress-free.

In the pine example I measured the reduction of diameter upon shrinkage and the width of the crack and was able to compute the radial vs tangential shrinkage. ( The things one does to postpone a difficult woodworking operation)