rear pad delam, split divinycell.

discovered a crack in the rail under the rear foot pad, water oozing out. I attacked it with a knife to have a look inside, and provide a bigger hole for the water to escape, and found this.



As expected the eps has broken down, but so has the divinycell. You can see the split running all the way through it.
I've never seen this before, has anybody else?

When I first cut into it, and the top layer of sandwich came away, leaving the bottom layer behind, I thought that it was a poor bond between the cloth and divinycell. But that's solid, both bits of d-cell have cloth stuck to one side, they've just separated from each other along that crack above.

Looks to me like the bond between the d-cell both top and bottom were very strong, stronger than the d-cell itself. I'd take it as evidence of a very strong build, it's impressive, unless the board is pretty new. Which brand of board, if you don't mind me asking?

seen a few times a custom slalom board that creased, a wave board had a big area that had done that & one or two warranty claim cutups. Guess once the eps splits the dcell must be the next weakest spot with the movement.

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decrepit said..
Mastbender said..

Looks to me like the bond between the d-cell both top and bottom were very strong, stronger than the d-cell itself. I'd take it as evidence of a very strong build, it's impressive, unless the board is pretty new. Which brand of board, if you don't mind me asking?

I'll take that as a congratulation, as I make all my boards myself.
The metadata on it's finished pic says 11 april 2011, so it's coming up for 7 years hard work.

Well then you should, good job on the construction, too bad nothing lasts forever.

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decrepit said..
It's in the sun right now drying out. I'll fit some higher density closed cell foam in the big hole I've made, and in a week or so it should be as good as new.

Question for ya. How do you get continuity of the top and bottom glass layers in the sandwich in a hole like that? Do you tuck the new bottom layer under the the old bottom layer?

In the post, I've carefully routed the d-cell back 20mm to expose the underlying glass. That's easy enough on a flat section, but right on the rail, I'll be going with Mark's method above.

It is meeting the glass under the d'cell as a butt join.

Not perfect but if you poke it under with an implement as some do, it is sticking a 0.25mm thick layer of glass in with a 1mm thick blade / scraper = void.



I think the continuity of the 2oz glass underneath the d'cell is least important of the whole layup- and any strength loss at the perimeter is made up for by the small amount of resin/q-cell mix around the edges of the d'cell join.

Interesting. I recall that the Boardlady described delamination as coming in phases, with a separation of the core being first, and crunching of the sandwich coming later.
I recently talked to an experienced windsurfer who builds his own boards. He does a few things differently than what I'd heard before. He uses a layer of carbon instead of glass between the core and the sandwich, reasoning it's stiffer and reduces the flex at the bottom layer, and thereby the stress on the core foam and the boundary. He also uses a high density foam that's about twice as thick as normal, and looks a bit different from divinicell, more like PU foam. He uses glass on top. His boards hold up very well, and he's a heavy guy (100+ kg) who sails a lot in swell. It's also quite windy where he sails, so a little extra weight from the thicker sandwich does not matter. Any thoughts on his ideas?

That's a clear example of the core having melted. Have you thought about trying for a refund?

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boardsurfr said..
. Any thoughts on his ideas?

I agree, where I need 1 layer of carbon it goes under the sandwich, if I need 2 it goes both sides.

carbon isn't good on impact, the glass and sandwich protect it.
Under the sandwich is more in tension with a compressive force, so I think the carbon is more effective there in reducing core fatigue.

That pic of mine has carbon both sides of the D-cell, because it's under the foot pads.