I only recently became aware of end grain balsa core. You guys involved in boat building have been using it for years. It comes in various thicknesses in 2 foot by 4 foot sheets. Sounds ideal for paipo and small kneeboard construction. You might even be able to laminate a stagger pattern to make longer boards. I looked around the internet and noticed wakeboards are using balsa core. Any of you guys ever use the balsa core sheets? Dale, you must have done this.
Hi Poobah, Youre right, end grain balsa has been in use for many years. Its natures micro-honeycomb structure. Among other useful characteristics, it has excellent compression strength to weight, often as high as 1500 to 2000 psi. In the 1970s I applied it inside the rail chines of flexible kneeboards and paipos. Small blocks, set side by side, were shaped to conform to the kneeboard/paipo glass shells interior contours and then glued into position with microspheres and polyester or epoxy resin. Very effective, offering flexibility, buoyancy and outstanding compressive strength. In flexible structures, end grain balsa was a superior replacement for the weak, lower-density of common surfboard foam... which would eventually point load in certain places, forming fatigue "hinges". The final result being breakage if not repaired or completely rebuilt. But working with end grain balsa in this way was very labor intensive. Later on I replaced the balsa with hand-pour high density polyurethane foam, about 10-15 lbs./cu. ft. Its also available in other densities/compression strengths, has outstanding bond to the shell, offers consistent, easy tooling and is much less labor-intensive… basically build a cardboard dam, mix, pour and shape. The time from wet pour to hard cure can be delightfully quick.
We use end grain balsa extensively in the boats that are built where I work.I have often thought about using it to build a board.There a couple of problems I can see in using it to make a longboard.Firstly it is end grain, structualy the grain needs to be running down the length of the board, not from top to bottom.End grain balsa is very easy to cut down the grain. I can see problems with to much flex and it trying to break down the grain. Secondly it tends to be quiet heavy. Balsa naturaly grows in different densities. To get much the same density in each block, the balsa is compressed under great pressure.So what may have been a 3" x 3" block is squashed to 2 x 2", so you need more balsa to to produce a given size sheet. It will also absorbe more resin. We pre coat with resin and let it gell before laminating. I dont want to sound to negative here, I think it is a good product and will work in smaller products like wake boards etc and what Dale was doing.But in larger,longer boards I think it will cause some problems.David.
David, During the 1970`s, I purchased roughsawn 4" x 4" and 4" x 6" balsa timber, usually in 6’ and 8’ lengths. I soon found it was necessary to have quite a few planks in the shop from which to select. The balsa I received had a wide range of quality, densities and weights.
Dale, When I first staryed using EGB, the sheets were made up with all different densities of balsa. Sanding the sheets after bonding was a real pain. You would be sanding away thinking about anything but the job at hand and bang you hit a soft patch. Thankfully I dont sand much balsa anymore.Though it is not such a big problem with the compressed balsa these days. I noticed the time on your last post, there is less than a hours difference in our post times. Where are you writing from. David.
David, Im on the central coast of Oregon. The Pacific Northwest, USA. I dont sleep as much as I should… afraid I might miss something! Ha ha!
Dale, That would explain it. The only other explaination would be that you were half way between east coast Australia and New Zealand.David.
Incredible stuff. We’ve built some but it’s a bit heavy for boards.
Here’s the photo again for anybody interested… 
John. Is that one piece of end grain balsa at the back of the fin box, then solid fibreglass? It would make sense to do that, to have a good solid hinging point.Is that the only place it is used in the board?David. p.s. Are they all Greenough fins? Nice collection.
David - It looked to me like the EGB was faired in as a transitional material between the foam blank and solid glass flex tail. I guess it would have been nice to have a close up of that area and a shot of the deck also. The fins are a mix of designs ranging from “tuna tail” Greenough/Liddle styles to paddle fins, Paul Jensen wood composites, etc. I think Paul Gross did most of the flex fins in the photo. I really felt (still do) that up in Big Sur we had one of the most eclectic assortment of surf craft assembled and that Matt and Kirk’s combined collection was a highlight.
We used egb for the transition area but we used roving to and later found that layers of volan built up like a fin works better.I have a new flextail in the works.There is no need for egb with the new ones.You can also take a board you have and retro fit it with a flextail.KP
My Turn. Who is building your flex?
Marc Andreini shaped it and I will do the flex after its glassed ,unless TB is up to it? your turn.
Mark Rabbidge wrote an article on flex that appeared in Australian Longboarding magazine earlier this year. He talks about retro fitting a flex tail to convential boards.Go to resources then articles here at Swaylocks “Tuna Swirls” David.
KP, Have you checked your e mail lately? Maybe I don’t have it right?..TB