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[tomway]

Now, i've probably done some silly things here  , but i'm hoping some people with experience playing with different combos of materials might pinpoint what they think the specific problem is.

So, for starters, the epoxy i've been using is a local brand. clear, wets out great, 2:1, good uv in sun tests. No specific application info. Basically, an unknown quantity. However, no other option based on my locale.

Foam: as indicated in another post, i screwed up on the densities, and have been using 10kg/m3 foam, which is prob around 2/3 of a pound. very light, and floppy, but shaped ok with care once the rails and bottom were on.

skins: 6oz (under) - 2.5mm balsa - 4oz over. outside glass is a hand lam, with epoxy fill coat.

I shaped 4 boards before starting to glass, and thankfully tested the first two before continuing.

Within the first week of surfing both boards are getting bad pressure dings, with evidence the skins are delaming from the core.

Now, i think there are possibly 4 problems, which do you think is most likely?
1) the glass schedule needs to be beefier.
2) the foam core plays more of a structural part than i originally anticipated, it needs heavier foam
3) the epoxy is crap
4) the epoxy resin/hardner ratio is wrong. I mixed 2:1 by weight as suggested by the distributor. However, the distributor may well know nothing, but didn't want to admit it. In test,  2:1 by both weight or volume seem to cure hard and dry although there is at least a 20% difference in densities (a cup of hardner weighs 20% less than a cup of resin). not done any strength testing though.

So, which point leaps out at you as culprit no.1? 

Thanks in advance!

you can see the boards on sugarpalm77.wordpress.com

 

[lemat]

I see boards made with 10kg home insulate EPS (o,75#) , 1,5mm balsa 4oz under and top. No dents, just some small foot prints after 2 years.
If your resin dry hard mix is not too bad. Too much hardener dry soft and sticky.  A bit too much resin dry hard but fragile. Too much resin dry soft. May be your resin need long time to completly dry or post cure. May be your under lam was too dry for good bond to foam. I think that 16kg EPS is better.

Soory for my frenglish

[tomway]

Hey mat

thanks for your reply

you obviously know your epoxy, great description of slight quantity changes

Could be that i didn't use enough resin under the deck lam and its too dry. good thought.

I've just done a double 4oz on the top of the next board and after a day or two the deck seems solid

Next batch of boards i won't take any risks. 16kg foam and extra glass patches in spots that take the strain

Took a look at your blog, like your boards and love your shaping bay!  Where are you in france? My wife, son and I will be over in the summer.

[lemat]

I am in Ondres near Hossegore and Anglet.

I found (plane and boat builder "secret") that it's good to put "silice colloïdale" (cabosil i think in english) to the resin for under lam. Silice give you a past (mastic) but it still wet fiber right and when you bag, resin stay where it's have to be, stick better and harder.

[wouter]

HEY MISTER
my guess is the foam sucks
usually what happens is the foam is still attached to the deck, but the foam itself broke down.
happens when the pressure on one point, locally, is too much. did you knee board it?
so, stiffen the skin up, keep the foam the same, to make it shear.
at least, that is how i understand it.
wouter

[mark venn]

Hi Tom,
use too much resin on the inner lam, board will be too stiff.  Sounds to me like you need more glass on the outside, one 4oz with questionable epoxy resin is probably a bit close to the mark! I would usually put 1 x 4oz all over with extra under feet and where you push up on the rails. kneeboards, you may get away with 1 x 4oz if you use deck pads.
Cheers
Mark

[tomway]

thanks wouter and mark

so, on the latest one i've done a double 4oz on the deck, and did extra wide laps from the bottom in the 'pop-up' areas - kind of beaver tails to patch where the hands get planted. Hopefully this will help out. As wouter says, the worst bits are where hands are planted on the deck near the rails (balsa prob a bit thinner there too after feathering the edge on to the d-cell rails).

I think resin may have been light under the skins though. I was perhaps a bit too keen to keep weight down. The wood skins actually return to the deck shape in the delam areas, but there's a definite void under them. I can see lemat's point about mixing cabosil with the resin to stop it disappearing in to the foam on the under-lam. Wonder if the benefits outweigh the loss of strength by doing this.

Hopefully get this one tested soon. Just fill coated it with PE resin with some tips from huie. Interested to see if I can debunk some myths about this. Small test pieces i did at the same time seem good. no obvious signs that it would chip more readily than epoxy. but time will tell i guess.

done many boards recently mark??

[huie]

hey tom   hvent been here much
so lucky i seen this      anyone doing sandwich these days dont use balsa josh uses palownia
to many prbms
wha t i have done in the past is flip the skin & seal the skin first then lam it up with 4 oz
let i go  when cured  scuff it up good sqeege a coat of epoxy over skin vac it on

never had delams till they at least get a floging

for your outer 1 layer with fin patches bottom
deck 1  4 oz        3/4 patch heart shape  x 1    4 oz

but i would recomend giving the balsa away

yes the poly will stick to the epoxy best way to test it is when you think it is cured get a bit of 120 sand paper
give it a try if it sands ok good to go   if there is any tack poly will f##k up       once you do a few youll know

cheers huie

[lemat]

I speek about silice coloïdale it's a tixothropic agent. It don't modify resin strenth "au contraire"...

I use PE on cure epoxy with sucess too. But on dings i found that PE crack (star ?) more easily than epoxy.

Sorry for my english.

[mark venn]

Hi Tom
No, haven't done a board for maybe 8 months, have given up the workshop as I wasn't spending enough time there.  Have enough room in the workshop at home to do shortboards though.
I would love to give pawlownia a go, but can't get any over here Until then, its balsa, cedar and HD foam! I always use SP Eposeal to seal the balsa before lamming the outer skin, never had any delam to my knowledge. Also never used PE to fill coat the epoxy lam, thats not to say it won't work, I defer to Huies experience there.  I know that PE gloss coats stick as long as the epoxy is fully cured.  any amine blush on the epoxy will however inhibit the cure of the PE, so make sure its clean and cured before trying.
Mark

[tomway]

Yeah, huie, I'm getting the balsa vibe (just seen the swaylocks firewire post hehe!) Actually I have a lot of options for wood here including a number of pawlonia like woods. Problem is getting them dry, stable and to an appropriate thickness. I'm not in a position to resaw yet, and though I HAVE used other techniques they add a lot of hours. Can also get dcell at 80kg/m but really expensive.

Having said that about balsa, the board that markv made me is starting it's 4th season now, balsa alround incl. rails, and it doesn't have a scratch. I surf some pretty hollow shallow waves, no airs or stuff, but I fall off a lot and get flounced by thick lips so i reckon that compensates  for testing purposes

Was that a double 4oz deck mark?

good tip with the 120g tack test. it's the little things...

I actually went overboard and scrubbed with hot water AND scuffed the top of the weave with 80g (as advised by the empire foam crew) AND wiped down with acetone (ahh, acetone, don't tell anyone... run away!) Perhaps just touching the weave with paper allows a bit of resin entry into the cloth and a better key? It is very slightly visible through the hotcoat, so cosmetically not so good.

local test ground:

[huie]

TOMO  did i not say this elswhere

if you sand through to glass you will need to repair with epoxy so it is best to do a bit more substantial hot coat ie. dble coat on laps around fin areas.



heres the deal once you get to know there is no blush         

 i never see it  myself?

i just make sure my laps are clean and go straight in and filler coat

i need to talk to that empire mob  haa''

acetone           throw it away you do not need it    f###king death juice 

[huie]

TOMO  did i not say this elswhere

if you sand through to glass you will need to repair with epoxy so it is best to do a bit more substantial hot coat ie. dble coat on laps around fin areas.



heres the deal once you get to know there is no blush          

 i never see it  myself?

i just make sure my laps are clean and go straight in and filler coat

i need to talk to that empire mob  haa''

acetone           throw it away you do not need it    f###king death juice  

epoxy lam poly filler poly gloss

[huie]

go hug your mum 

[tomway]

huie
you did say sand throughs would need epoxy repair. won't do that again.
must be those empire guys trying to throw me off scent  . fool me once...

beautiful work on the pictured board. I've been in awe since i saw those first cdd shots a year and a half ago. the burred wood is a veneer (?) so the balsa also is very thin?

Mark, sad that your workshop is gone. it was a dream setup you had in there. You've still got all your tools?? still working on boats? I'll email. Want to catch up in june if you're around.