Coaming boards revisited - apparently quartersawed wood makes a difference...

[chrisncate]

When wood is quartersawed, it only expands/contracts regarding it's thickness, not it's length or height.

[Hartley18]

He's quite right. It has to do with the way the grain runs.. but there'll still be a small amount of expansion dependent on the thickness of the timber, it's moisture content and the temperature range in your neck of the woods.

You're using CPES, not straight epoxy - yes??

[CalebD]

Quarter sawed (or sawn) wood is superior in some ways.
Quarter sawing - Wikipedia, the free encyclopedia
I'd still use butyl to bed the coaming boards even with an epoxy coating on them.

[mitiempo]

Quarter sawn wood is better and has more stability, but as it is solid and not laminated for the ultimate in stability it should, in my opinion not be epoxied. I would compare it to fiberglassing a cold molded boat vs doing the same to a traditional planked boat. The cold molded boat is stable and the covering should not have any problems, but the planked boat (quarter sawn or not) will move enough to crack the glass covering.

Epoxy is great for modern (laminated) construction.

Traditional finishes are best for solid wood structures that will move, however little.

In my opinion anyway.

[Hartley18]

Brian, as the current owner of a wooden boat, I, for one, completely agree with you, but my question still remains:

I'm assuming that by "varnished epoxy" C&C is referring to the use of a Clear Penetrating Epoxy Sealer (CPES) product under the varnish to increase durability - not an epoxy sheathing solution - which is something I use all at the time and especially on exterior brightwork like my bulwarks.

..but I could be wrong.

[mitiempo]

That is the only type of epoxy I would possibly use on solid wood.

[merc2dogs]

Quartersawn is the way to go reduce expansion and contraction, it can also be the prettiest way to cut wood. But due to the way the grain runs it's not always the best for applications that can be stressed. If it's supported only on one edge, loading the 'free' edge causes cracks and splits a lot easier than other methods of cutting.
Plane/slab cut lumber puts the grain at a better orientation for strength across the width of the board.

[hellosailor]

I wouldn't think quartersawn is relevant to this. No matter how the log has been sawn, the length (or height) of the boards will come from the length of the trunk, and when wood shrinks it doesn't shrink significantly in that direction. The shrinkage and swelling is radial, i.e. the trunk gets fatter and slimmer, which will translate into the width or thickness of the board, as opposed to the length. Again, no matter how it was sawn.

You see this is log cabins, which when properly built allow for the logs to slip and move to accomodate the shrinking widths as they age and get thinner, although the lengths of them does not change.

The big difference in "laminated" wood would be if you were using veneer-cut (rotary cut) wood, which is used to make plywood. Much more stable because the wood is literally sliced from the log the way you "peel" paper from a roll, and then the plies are glued alternately cross each other to counter any movement. If you were building up laminates from thin sawed boards though, you'd still be working with boards, not veneer cut.

[deniseO30]

Chris.. think what was being done long long before epoxy... Varnish.. best way is one of those type of finishes. Epoxy just won't last in the heat, sun, and temp changes (imho)

[hellosailor]

"Epoxy just won't last in the heat, sun, and temp changes "
So epoxy would be unsuitable for, say, building fiberglass composite hulls that were going to be exposed to the sun?

A little paint or varnish on top, a little care...epoxy might not be so bad for long-term use. Heck, wood doesn't always do so well out in the sun by itself either.