Hi, I am thinking about building board with paulownia wood core (about 130 cm by 39 or 40). I have seen boards that were made with smaller pieces of wood 10mm by 30mm (and lenght of the board) glued together to create the core.
1. Was it done on pupose or was it done because it is hard to find one continueos piece of paulownia wood. How does it affect flex and weight of the board
2. If you shape such a core to the thikness of 10 mm between footstraps and taper at the tips can you still create concave and rocker just by using rocker table and vacuum bagging process (just like you can do it with foam core or do you have to shape concave bottom before laminating?
3.does paulownia wood core has any advantages over foam (corecell)
4.do you know any suppliers of paulownia in US
5 any suggestions regarding laminating? i am trying to get strong board but with considerable amount of flex for soft landings and comfortable ride in chop since i had a knee injury.
Thanks for any suggestions

Bump. Just found this note -- thinking about the same thing -- and would be curious to know if anyone had any thoughts on this...

Thanks!

wood tolerates flex and impact better than foam (less denting, hard to snap)
you can get paulownia in US, but have to dig around for it.
Wood cores are done from laminated strips to prevent warping and get good (consistent) flex.
It is cheaper to glue up smaller pieces of wood, also....
Paulownia should flex a lot, and it's light and easy to shape.
I know you can force a thin flat glued up blank into a concave on a rocker table, as long as it is not "extreme" in curvature. 10mm thick might be too thick though, not sure. Depends on the concave and the wood....
You could also glue up the blank on a "cylinder" that has no rocker, but defines the concave (or part of the concave) then flex it onto a rocker table after it has cured. This is a way that works to force a little more curve into thicker layers. But you probaby don't need to go that far, and you would not want to prestress the wood TOO much or it will no longer resist snapping so well

We currently use Paulownia Wood Cores on our boards.
What is extremely important is the way the woodstrips are put together.
Ours have jaggered ends, almost like zig-zag which makes an extremely good bond between each segment when glued together.
This makes the core more pricey to produce but ultimately keeps it true for longer and also makes it stronger.
As always you get what you pay for and not every wood core is the same even when the same type of wood is used.
So the things to watch out for is the connection between each strip of wood and that the wood has been stored for long enough and at the right humidity and temperature.

Here a short animated video of one of our Boards with a Paulownia Core.

I think it may be apples and oranges?
For production you buy containers of logs, boards or premade strips, so you get better results with fingerjointed strips, I guess, an engineered material evens out the variation, when you potentially build one kiteboard from different pieces of lumber, trees, etc.

For the one-off custom or DIY, I think you might want a different approach.
Find a good piece of wood, resaw it into full-length strips, glue the strips to avoid warping, etc.
I also think this would be good for the amateur light glass jobs and thicker strips....

But I don't really know Paulownia, I suppose segmented strips could arrest shear stress propagation along grain, if that is a factor in the durability of this wood?

not sure why they use multiple strips. i've always used 2 pieces and never had a problem with that.
IMO board manofacturers use multiple strips cos it looks better, or just because that's what everyone does. (when other kiters look at my boards, they ask: will it brake in the middle? -- noone would if it was made out of 15 strips )

(but my boards have no concave.)

pablo

btw, each board has around 80 pesos in kiri (around 25 usd)

Pablo,

Sweet looking boards! Pretty sure board manufacturers use multiple strips b/c it's cheaper. It's a lot more difficult to find large pieces as sweet as those that you've used than it is to find marginal piece where they can cut out the knots, checks, etc. and then glue it back together. Just a thought. Either way, I'm having trouble finding the stuff in the US to make up a board. Anyone know where to find Paulownia in the states?

Thanks!

There are growers in some southern states.
Some nurseries may also have trees, they grow quickly....
The growers also sell samples of lumber....
Google will find you more info about all this stuff than I could write here in a week.
Swaylocks.com is a good board building resource, so are lots of boatbuilding type websites, for general information that would be useful.
If I knew somebody that stocked paulownia lumber I would tell you (after I bought a few boards myself).

Hi Maybe someone know what's name this Paulownia wood for kiteboards. I mean that paulownia have many type.Which is the best for it??
Dan

lots of surface area in a decent glue joint for a 1/4 " board,
so i would not worry about the need for something like finger joints.

for me the need for multiple thin strips is more of a practical matter.
most boards available to me come as 3/4" think planks, usually flat grain.
( the exception would be 1/8" balsa planks or wood veneers sold for furniture and now surfboards )

lots of waste to plane 3/4 " down to 1/4 or 3/8 core.
so i rip saw the 3/4" flat -grain into multiple 1/4" quarter-grain strips

you can glue/assemble the strip onto a rocker table if you wish.
but without a matching piece on top , or steaming , or something else to resist the bending shear it will just return to 'flat'

i'm not the first to figure any of this out:
you can take a peek at john B's thread for a wooden mako
viewtopic.php?f=1&t=2359282&hilit=wood+mako
or do a quick google search for building a strip built kayak

two thins sheets of wood on the rocker table will be fine
or
wood core with 4 oz glass laminated top and bottom to set both rocker and concave

regards,
-bill