Firstly, apologies for using the term compsand, since I know it’s a brand, etc…but at least it conveys the general build method of my board. I’ve just recently finished my second board, being a 5’6 x 20 3/8 x 2 5/8 EPS/Balsa composite and I have an unusual delam issue. Let me explain my build (sorry, no build photos at the moment):
I've used 19kg/m^3 (M-grade for the Aussies), which is about 1.3# EPS, for the core (from RMax if anyone in Melb knows them). Seems like a good quality foam, shapes very nicely.
I've skinned the core with 2.5mm balsa (aero-modelling sheets 915x100mm), with 6oz glass between the skin and the foam. I free-bagged both skins at the same time, and both adhered very nicely, the bottom skin following my double concave perfectly. If you're wondering why I used 6oz under the balsa, it's because I have a 100m roll of the stuff, and didn't want to buy a lighter cloth just for this.
Balsa strip rails added and shapped.
I laminated the board with 1x6oz bottom and 2x6oz deck, no issues there.
Total board weight with 5 probox boxes came in at 3.5kg. Not light, but around the same weight as my standard PU/PE 6'6 from a local shaper.
[img_assist|nid=1056450|title=Board #002 - Balsa/EPS 5'6 x 20 3/8 x 2 5/8|desc=|link=none|align=left|width=640|height=427]
[img_assist|nid=1056449|title=Board #002 - Balsa/EPS 5’6 x 20 3/8 x 2 5/8|desc=|link=none|align=left|width=426|height=640]
Now onto my problem…I’ve surfed this board maybe 10 times, got it in the water just after Christmas, in a range of conditions up to 4ft (Vicco scale, ie overhead), and I am very happy with the result. There were no pressure dents at all, until my last surf on it when after a wipeout, the deck-side came down hard on my head. This caused a pressure dent about 120mm long by 70mm wide and maybe 2-3mm deep, which in itself is no big deal, I’m not precious about boards. However, later on I noticed that the patch of glass around the pressure dent had that delam feel about it. The wierd thing is, the glass hasn’t lifted off the balsa, and the balsa hasn’t lifted off the foam. It seems likes the fibres of the balsa have separated with the bottom half of the sheet remaining with the dented foam, and the top half ramining with the glass. The glass feels floppy, like there is probably less than 1mm of balsa remaining with the glass, but there is no visual indication of a delam. In terms of fixing, I was just going to make a small incision and inject some resin, but I’m more concerned about how to avoid this in the future.
Have any of the compsand guys encountered this? I am considering using bamboo on a future build, but I like the look of the balsa planks! Should I use a thinner balsa sheet, ie 1.5mm instead of 2.5mm? Any other advice, suggestions, etc?
“It appears that your core failed in shear” - nailed it. Had that happen a few times and I couldn’t really figure it out until I took the zone apart. I’ve tried injecting resin and revacuuming locally, which worked okay, and removing the horizonatally split wood, faring in another piece, and then revacuuming as well. More work but probably a better long-term fix?
I have same problem on 2 boards with balsa deck and i repair a firewire with same problem on ding rail: fiber of balsa separate from each other. It’s a problem with balsa, and it’s accelerate if water penetration. On the last one with balsa i seal it with hot fluid resin, no problem but i go to timberflex style (thin veneer over stronger foam), boards are flexier and work better but dent more.
I have same problem on 2 boards with balsa deck and i repair a firewire with same problem on ding rail: fiber of balsa separate from each other. It’s a problem with balsa, and it’s accelerate if water penetration. On the last one with balsa i seal it with hot fluid resin, no problem but i go to timberflex style (thin veneer over stronger foam), boards are flexier and work better but dent more.
I have same problem on 2 boards with balsa deck and i repair a firewire with same problem on ding rail: fiber of balsa separate from each other. It’s a problem with balsa, and it’s accelerate if water penetration. On the last one with balsa i seal it with hot fluid resin, no problem but i go to timberflex style (thin veneer over stronger foam), boards are flexier and work better but dent more.
bummer about the board man. i guess what Jeff said about repairing is true.
open it up and see what really happened
sometimes the balsa breaks away from itself. sometimes the styro just breaks from itself. Never the bond between glass and styro. only sometime the bond between the glass and balsa [when a board breaks completely this happens a lot]
so, open her up, find out what the problem is and come back to us or your own logic for a better build next time
bert broke many boards before he got to where he is today [thailand??] still want to surf a longboard but they are ultra hard to come by here in europe
he always said that you have to make it flex. does your board flex?
Thanks for the input guys! I agree that it is likely a shear failure resulting from a local weakness due to the dent.
@cj, thanks for the reading, it was quite informative. BTW, the whack on the head was hard enough to make me see stars for a minute, but not enough to end the session!
@jeff, I think I’ll just inject resin and revacuum. This isn’t my everyday board, so a simple fix should last long enough.
@wouter, I have a peek inside when I make an incision to inject resin, but I’m pretty sure the balsa fibres have pulled apart due to shear. As for flex, the board is a lot stiffer than normal, since I have 26mm of balsa strip rails / perimiter stringers. I’m beginning to see how this compsand and/or timberflex approach isn’t as straightforward as I first thought, there’s a lot to learn…oh well, it gives me an excuse to build more boards!
@lemat, that’s what I was beginning to think, it’s a balsa problem. I’ve read here that people have switched from balsa to bamboo and won’t go back. If I can find a local bamboo veneer supplier that does 0.6mm, then I’ll do the next one with that instead. At the moment, the only supplier I’ve found is an hour away and only has 1.5mm veneer, which probably will be too heavy. The other option I have is to use thinner balsa, say 1mm and hope that in the course of bagging the skin and laminating the cloth, the balsa would become completely saturated with resin, thereby preventing any separation.
I have had a couple of boards delam from the balsa skin. When you take it apart you notice there is a thin layer of wood stuck to the glass and the rest is still attached to the foam. This happened under glass on fins, but never from an impact to the board. I noticed the way it delaminated when I started fixing it. My fix is to go to boxes.
The other delams seem to come from using extra light EPS cores. The foam we get here from Lowes is very soft compared to Home Depot foam which is soft compared to 2lb construction type EPS. The Lowes foam boards has spots on the deck where it feels spongy, but it also feels like the whole skin is still intact, but flexing over a soft core. I have a bamboo skinned board that has had the same problem. I know the skin is water tight because it will balloon up if left in the sun, but it has a soft flexy feeling skin. I have no plans to fix these, I’ll ride them till they die.
What Paul R says seems to work. Some of the boards we made had enough resin under the balsa to saturate through when we vacuumed them to the foam. Those have very strong skins.
If you want a seriously strong board, skin a PU blank with balsa. My brother and I have a couple and they are solid. I had my head shoved into the deck of one and all that happened was I got a serious bump on my head. The board had no signs of an impact. The down side of these boards is they weight more, but in 5 years they’ll probably not have any signs of wear.
In the last several years, I have made a bunch of EPS boards without the wood skin because I can make them so much faster. That would be one work around, just use another layer of cloth and add color.
I seem to recall Bert Burger mentioning a couple of things about "wood impregnation" and, in the absence of an autoclave, "breaking out the solvents."
I suspect there is a solution in those two quotes and it has to do with what Sharkcountry posted about some of his skins being saturated through with resin.
I also have seen fiberglass peel off balsa and have a thin layer of balsa still stuck to the glass... as if the balsa had separated from itself.
since your in oz I’d switch from balsa to paulownia
less fiber seperation than balsa about the same weight.
This happens on PU glassed boards as well
my brother dropped my alexander gemini on its rail on the concrete and it developed some rail shatters
the next thing I know I have a large delam bubble on the bottom next to the shatters in the deep concaved bottom.
I think the rail shatter provided some release from the exoskeleton tension of the glass as it was pulled tight into the concaved bottom causing it to release from the stress and bubble out. Never saw anything like that before.
finding a way to infuse your balsa panels with some sort of highly penetrating sealant without increasing the weight is I guess one of bert trade secrets. As water penetration from pinholes and dings are a balsa composite’s worse nightmare. That’s why I like Gary Young’s technique of using HD foam/XPS for perimeter rails and layers of epoxy saturated bamboo veneer in place of fiberglass and then sealing the exterior with hurricane proof glass plastic skin sheets for extra sealing and protection.
Thanks Paul and Oneula, I’ll look into some local paulownia suppliers. I guess the next board will have either a bamboo or paulownia skin, depending on which I can get more easily/cheaply.
Really light balsa is not much good for compsands....it will absord far more resin that tighter grained heavier balsa, so there is no weight saving. If using poly resin,I prime with 5% styrene and it will seal and not absorb much resin.........at minus 80 to 100 kpa of vacuum, you can suck the resin right through light thin balsa and weaken the bond , particularly on unprimed eps...........you can also spray the shaped board with clear acrylic before glassing,,,good sealer and good bond with a poly glass-job
hi kayu that is not entirely true but your right as well. you can make an under 4 pounder with light balsa if you layup with a brush or prepreg. the board will dent and ding a bit but not snap easily. you know what i mean if you want light with reasonable durabilty then balsa nails it but you gotta be careful with the resin and finish in 2 pac. people cant expect light boards to last forever. but you can expect a year or two out of super light balsa if your lucky or careful. still beats a 6 month poly IMO. but then again light boards are not my buzz anymore . im more concerned with crowds then board construction or design
hi kayu that is not entirely true but your right as well. you can make an under 4 pounder with light balsa if you layup with a brush or prepreg. the board will dent and ding a bit but not snap easily. you know what i mean if you want light with reasonable durabilty then balsa nails it but you gotta be careful with the resin and finish in 2 pac. people cant expect light boards to last forever. but you can expect a year or two out of super light balsa if your lucky or careful. still beats a 6 month poly IMO. but then again light boards are not my buzz anymore . im more concerned with crowds then board construction or design
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Hi Paul , many ways to skin a cat , yeah. Its not often that I need to go sub 4lb... and if its a light eps core , 4lb is way too light for the floatation of the foam IMO...for a pro maybe ok. The blanks i do make for some shapers are made considering the floatation, and not so much the finished weight.....which is the main reason I prefer the balsa a little heavier , so the sealer doesnt drink so much resin.....in any case , mine are a different animal, not compsand........carbon under thin light balsa is the sub 4lb special , if people are prepared to pay the cost ! haha!....cheers