Laminating Balsa

It'll epoxy with a balsa core.

A seat, can have more than just a 300lb distributive load. Impact load and a centered load.

The second problem (without going into the calculations) is grain of the Balsa, will be in shear load with the end grain. I don't know if there is reinforcement brackets/braces under it.

So I would say no.

The balsa is pretty much irrelevant, it's merely holding the f/glass into a box section.
I'd say it depends how many layers of f/glass and how well you apply it. I'd guess that 2 or 3 decent layers would do it.
Not sure what you mean by end grain balsa... if the grain isn't running along the length of the seat then the balsa is a waste of money, you may as well make a box section from cardboard with some internal cross bracing and glass over that.
I have no physics, maths, or great experience of f/glass to back this up.... I'd just use wood and forget the glass, but that's me.
Del

To me it seems he wanted the end grain to show as the seat pattern.

A seat? As in in something that moves and bounces? nor like a chair.

Is there a special need for this lightweight wood? Going ballooning? Solar racing?

Is this a continuous duty seat or for a few hours a year?

It really depends on where, how much and how the load is being picked up beneath the board? Is it only at the ends?

As Del said. It's all about the layers.

..I'd round the edges a bit..

It all depends on the support....I mean if it's sitting on a block of wood, then you don't have any need of support structure....If it's being hung by two steel cables from the ends, then much more is needed....Will you wrap around all the edges for added structure integrity? If it's supported around all the edges, then you should be fine with 2 or 3 layers...

No!

And end grain balsa is blocks held together with scrim cloth so it can be bent into complex shapes. Not very strong.

Why e-glass and not s-glass, which is stronger.

I say 5 plys minimum may hold the weight, if it is applied properly and forms a box beam structure.

If you are contouring it, all bets are off.

More details are required for any useful answers.

I pictured a very sturdy 'butcher block' type of arrangement, with pieces very securely glued together. Who is right here?

A butchers block type arrangement would have V little strength. Like those bogus karate demonstrations where they use end grain wood you could sneeze on it and break it.
A butchers block is only strong because it is supported underneath. If it was just supported at either end it wouldn't take much load.
Del

The core goes into compression and tension keeping the skins separated. It is not a cosmetic covering you are making, but rather separating the layers to make a beam, with the moment of inertia constrained to the upper and lower skins.

I think you need to read my other replies and see my post in full context... you seem to be confusing me with an idiot.

Del

Google, "end grain balsa". It is not securely glued together. Its used to form complex contours that are then skinned over with fiberglass and resin when boat building.

It is NOT suitable for an unsupported seat.

My question..Is the balsa glued together , edge to edge,in a panel, or is it, as suggested, held together only by a scrim cloth, with space between the blocks? Makes a difference, as with building curved surfaces out of end grain balsa and foam blocks, one must force a resin / filler mix into the open joints as you laminate. Have used both in boatbuilding. Go to Gougeon Brothers, among other sources...

I have no way of knowing, it's not my balsa.

We have a "seat 12" x 30" using 5/8" end grain balsa.

[With] "8 oz/sq yd e-glass epoxied to each side" be strong

enough to "support 300 lbs distributed load".

Who knows?

Yeah, curious also. End grain blocks are generally designed for designing structural curves, and when bending, one side opens and the other compresses. Oh well, maybe he will chime in...

This is so small and so easy to build and test!

It is no bigger than a sample test panel.

Let's see some test results!

I'll leave it to you.

<bye>

Try it - it will probably work.

Years ago I made a canoe out of 1/2 inch thermal set foam (no real structural strength) and applied a single layer of 3 oz fiber glass to each side. The test section (1 square foot) supported at the edges on bricks would not yield with me jumping on it. It becomes essentially a box beam with the filler keeping the top and bottom layers separated. The top layer goes into compression and the bottom into tension. The greater the separation the more rigid the panel. Wrapping the ends also helps. The center of the core takes no real tension or compression. (you could use cardboard). 50 years ago balsa was used in a sandwich construction for the bottoms of fiberglass power boats, worked great as long as you didn't puncture the skins, then it became water logged and rotted.

This may be of interest for you for your project.

http://www.compositesworld.com/articles/getting-to-the-core-of-composite-laminates

It has some broad descriptions of composite structures.

The canoe I made was using an AIREX foam - looked like the C71 - but again that was 50 years ago!

What you did with thermal set thermo-set foam bears little direct correlation to balsa wood.

You are correct in thinking that the outer skin forms a beam like structure, but foam has equal strength in all directions. Balsa wood does not!

Del is correct.

Consider the likelihood of no-one else on this forum having done this before...