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board repair question

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Created by gofaster 1 month ago, 19 Apr 2019
gofaster
87 posts
19 Apr 2019 6:16PM
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I thought I would have a go fixing this board (RRD freestyle) It had a big soft area in front of the straps and cracking right across. As can be seen in the photo the pvc foam layer is cracked. My plan is to lift the pvc and put in some thin eps sheet to build up the squashed eps, glued with gorilla grip, then some replacement pvc, then cloth over it all. My questions are , 1)there seems to be a thin cloth under the pvc foam - do I put something in there? and 2)the deck seems to be 1 layer of carbon/kevlar. Can I just use glass over this instead? I don't care about how the repair looks or weighs, just get the board going again.


decrepit
WA, 9108 posts
19 Apr 2019 7:35PM
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The underlying cloth is a tension element in the sandwich construction. If you want to restore full construction integrity, there really should be an overlap, (about 3cm should do), between the good part of the old and new cloth you put in. The cracks where the sandwich has failed is primarily in this underlying cloth, so not tying the repair into the good good cloth will lead to a fairly quick fail.

Are you sure it's kevlar, a lot of resin has a kevlar like colour, and can make glass look like kevlar?
I normally use a carbon patch in the area around the footstraps to add stiffness to the sandwich.
That area is right under your feet, I'd certainly be using at least 2 layers of 4oz glass and 1 layer of 6oz carbon.

forceten
654 posts
19 Apr 2019 10:10PM
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I question it's kevlar also , the advise above is good.
you can do what ever you want, the difference is in how it may hold up. See boardlady.com

My procedure, would be remove any wet EPS, crushed .etc ..if needed to the bottom , fill entire area with pour foam, 8lbs, it's 2 stage, not as light as Diviycell or core mat sandwich material , but no other epoxy is needed.
Cut the excess foam off after it dries to a layer below the surface. Epoxy carbon then glass to fill gap, using marine epoxy.
Sand smooth, shoot with grey primer, sand lightly.

gofaster
87 posts
20 Apr 2019 1:01PM
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Thanks you guys. Two different approaches. I've looked at the board lady website, and old seabreeze posts, but this has confused me a bit. I've done kevlar racing kayaks before but this sandwich construction is new to me.

Photo is after i investigated further. There is a woven running along the middle of the board, and very light woven to the sides - tissue? The outer skin is carbon/kevlar. The eps just appears squashed. Dry.

If I understand correctly, Method 1 above is to cut out the damaged woven and patch across it with carbon. Would this be only on the central thicker woven, not the parts to the L and R? ( they are very thin)
How to fill the space between the eps and the cloth? If the gap is quite small(10mm), is it possible to just use epoxy with filler added? (cheaper)
Presume pvc foam on to the cloth, then glass over this.

Method 2 is to cut out the woven and patch the eps up to the deck level, with pour foam , then carbon patch and glass over that?


decrepit
WA, 9108 posts
20 Apr 2019 1:35PM
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The sandwich is like a beam, it has tensile elements on the outside and a compressive element on the inside.
Leave out the tensile element on either side and it will bend easily one way but not the other.
The external cloth also has the job of protecting against impacts, so there's more cloth on the outside than inside.

Carbon kevlar as you probably know is good for impacts and rigidity. This is probably just a patch under the feet.

My question here is, have you cut that carbon kevlar or is that it's original shape?

If that's the way it was, then that could be the reason for the damage, it didn't extend far enough past the foot pad area, and made a "hard point" where the board wanted to flex.

As far as the pour foam method is concerned, it's an easy way out, and I've used it in smaller non structural areas. But this spot is part of the area, where most of the loads on the board are. Changing the entire construction method at this point is risky, an overly soft or hard point here, is going to change the way the board flexes under load. If one point flexes more than the rest, then that will fatigue and give way. My aim would to try and replicate the original as much as possible. And if the carbon/kevlar patch does end as in the photo, make an exception here, and extend that past the footpads, ending in a pointy shape, DO NOT cut it straight across the board.

You probably don't need to use carbon/kevlar, as the Kevlar is about toughness not stiffness, straight carbon would be just as close to the original sandwich stiffness.

forceten
654 posts
20 Apr 2019 10:22PM
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Kevlar is a pain to work with. It's pricy as I recall even compared to carbon. I seriously doubt it's in there.
i asked a shop repair person about technique and materials to make my own board, after speaking and listening said, there's more than one way to make a cake.

decrepit
WA, 9108 posts
21 Apr 2019 9:32AM
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Select to expand quote
forceten said..
Kevlar is a pain to work with. It's pricy as I recall even compared to carbon. I seriously doubt it's in there.
i asked a shop repair person about technique and materials to make my own board, after speaking and listening said, there's more than one way to make a cake.


That's definitely a carbon/kevla composite in the pic, I know I've got some just like it.
And I agree it's a pain to work with, It's hard to tell when it's wet out, doesn't change colour. And if it gets to the surface is almost impossible to sand.

Mark _australia
WA, 19092 posts
22 Apr 2019 11:43AM
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That definitely their full carbon/kevlar deck.

Under the PVC foam is just 4oz glass and a yellow resin.


Forget the rocket science part as you are doing a very big structural repair in a highly stressed area, so if your carbon layer goes a bit further toward the rails than the factory one does, you won't be doing any harm. If your glassing is a bit heavier it won;t do any harm. The thinner looking stuff near rail that you describe as tissue may just be the graphic sticker.
There will be at least 4 layers of glass going around the rails. As long as its all blended out nicely and not straight across the board as it is currently. You need to make that repair into a big diamond about 50cm x 30cm

Forceten's method not possible here as we don't get 8lb density polyurethane foam here, the best you will get is about 35kg (2.5lb ish or something) and it has too many big voids. Only use it for small cracks.

Best is to cut out the big diamond shape then see just how bad the styro is. Small areas you can glue in more styro with a single part urethane glue, or look at decrepits thread where he routers out an inch deep over a big area and puts a big slab of foam there to build it up.
The styro is not that important, as long as it is perfectly flat and no spots that are way softer / full of multiple cracks. Well and as long it is the right depth too to avoid lots of filling after you replace the PVC / top laminate.

Then its just a case of 4oz and 3mm PVC / Corecell
Then feather out edges and 1 x 6oz carbon or 6oz CK, then 2 x 4oz. Maybe 3 x 4oz glass if you are only using e-glass.

** if you are re-glassing anywhere in the standing area between footstrap inserts- extra layer of 6oz carbon there. At least.

gofaster
87 posts
22 Apr 2019 7:01PM
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Thanks everybody.
Photo is of yesterday's digging. Removed all the broken foam and glass from the inner layer. I made a diamond shape with curves, - but not as big as 30cm. Nervous about that. But i will cut the front edge back so it is not across the board as i can see that could act as a "knife edge". Will sand the edges so they make a skarf joint. Don't know how that will go with the kevlar.
I'm going to fill the eps layer with slices of eps and gorilla glue, then sand it off to the below pvc level. Then the epoxy/glass over the central existing glass layer - how much overlap?
I'll see if i can find some divinycell, but I found some foam core board - has a layer of cardboard either side of a foam core - comes off with water. Probably not the right density ( feels a bit soft, whereas from memory the divinycell/hexcell is quite crisp?) close enough? or not? Epoxy pvc layer on to the glass and eps at the same time as the above glassing.
Let set.
Feather the edges, then apply the carbon and glass layers. How much overlap to the existing board surface? Are the layers to be the same in size?
will the new surface be higher than the existing?
not worried about finishing it flash like, but need some grip on the deck.

Its slightly intimidating but feel the fear, then get on with it....







Relic
TAS, 751 posts
22 Apr 2019 9:36PM
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This was two pieces. Unorthodox but still going strong after having the absolute **** sailed out of it. Use single bias carbon 3mm pvc in the middle s-glass with carbon fibre on top as per pics. More steps if you want by PM
It deals with torsional and shearing forces in one go for the scientists out there. Proven method stronger than original.







forceten
654 posts
22 Apr 2019 10:41PM
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2.5 pour foam, should work fine, the EPS in this board is 1.5 at most. I can't think of many repair material that wouldn't be as strong or stronger than what's under the top layers. I like KISS, for me , keep it simple stupid. And as previously said, more than 1 way to bake a cake .
in the photo, I see a material that can be carbon hybrid, maybe Kevlar / carbon. maybe the other carbon is removed already.
The property of Kevlar when sanded it will fray, badly, particularly the edges, unlike glass. I don't know what this board is supposed to be reinforced with.
If it's kevlar or not, mute point, don't use it to fix it.

Mark _australia
WA, 19092 posts
22 Apr 2019 10:47PM
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^^^ Yep all kinds of ways will work.

gofaster- you're onto it.
I can send u some corecell offcut big enough if you want - or maybe somebody close to you will pipe up? I remember how hard it was when I needed just a little bit of something....

Don't worry about sanding the kevlar, it will come off but just leave fluff, which will be under the laminate you add anyway. After the corecell is bonded on, try to sand out the top laminate which is say 1mm thick to make a 20mm ish bevel......... sanding disc in angle grinder goes well, a variable speed 7" sander/polisher much better

Then you will cut you carbon or CK exact, then next layer of 4oz glass say 1cm larger all round and same with next. After that you can add a layer of glass over the whole job to be say 5cm bigger al round, and that will be easy to blend in as its about 0.2mm thick .... won't see it.

If you really want to go nuts I could send u some CK offcut that matches (they don't sell the H-beam looking pattern in Australia) and corecell...
but as per decrepits suggestion, normal 200gm carbon will be fine and less hassle.





forceten
654 posts
22 Apr 2019 10:54PM
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Do you have core mat, it's cut, serrated with a net on the back, it curves to match the area?
Adding these, adds weight , more so with the epoxy .

Mark _australia
WA, 19092 posts
22 Apr 2019 11:08PM
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^^ exactly- it adds so much weight why would you?
The lightest version - Soric honeycomb coremat - is about 6x the weight of corecell when soaked with resin.
Geez, plywood soaked in resin would be better.

Do it right. Corecell sandwich.



As to your pour foam- its great for sticking the cracks in styro back together, but not good for building it up higher like he needs to do. Our 2lb ish stuff sets with a million voids up to about 1/8" dia., so if you sand that back, its almost as bumpy as the styro he is trying to fill so its a waste of time. We're trying to make it simple,less effort and strong not inventively unconventional and frustrating for a first timer.

Then again what would I know I have only repaired a couple....

hoop
WA, 1560 posts
23 Apr 2019 1:44AM
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Just my 2 cents.
It's too fooked for a project if you're still getting the basics together. It will be expensive and time consuming for an average outcome.
Find one that's a bit less fooked and go from there.

Cheers, Hoops

forceten
654 posts
23 Apr 2019 5:24AM
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Select to expand quote
hoop said..
Just my 2 cents.
It's too fooked for a project if you're still getting the basics together. It will be expensive and time consuming for an average outcome.
Find one that's a bit less fooked and go from there.

Cheers, Hoops


This has some merit. I have all the materials , unless I run outta epoxy.
Income has little to do with it, it's priorities, the lad needs new shoes he goes barefoot.. no not really.lol.

forceten
654 posts
23 Apr 2019 5:30AM
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Select to expand quote
Mark _australia said..
^^ exactly- it adds so much weight why would you?
The lightest version - Soric honeycomb coremat - is about 6x the weight of corecell when soaked with resin.
Geez, plywood soaked in resin would be better.

Do it right. Corecell sandwich.



As to your pour foam- its great for sticking the cracks in styro back together, but not good for building it up higher like he needs to do. Our 2lb ish stuff sets with a million voids up to about 1/8" dia., so if you sand that back, its almost as bumpy as the styro he is trying to fill so its a waste of time. We're trying to make it simple,less effort and strong not inventively unconventional and frustrating for a first timer.

Then again what would I know I have only repaired a couple....


Using pour foam it adds no additional epoxy until you layer..carbon..glass at which time the voids holes are filled
I don't think it soaks in much.

I think i agree , we disagree.

forceten
654 posts
23 Apr 2019 5:44AM
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Left is the inside of a Mistral tail section , EPS, prob 1 lb. On the right is the pour foam , cut off portion from box installation , it's not sanded, I don't think I have a device that would measure the imperfections.
At times the surface texture has some irregularities, nothing that a smear of epoxy wouldn't cure.
its not as light as other things, but it's easy peasy, and in grams .. not so much

Mark _australia
WA, 19092 posts
23 Apr 2019 10:23AM
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I am talking about our "pour foam" that we get in Australia - if you keep saying it will look like that it won't man.
All good if you do it that way.... but this is a forum question DIY - its about telling a first timer how to get the easiest strong result. If he fills that with our "pour foam" it will take two days to fix the mess that looks like the surface of the moon.

FormulaNova
NSW, 8623 posts
23 Apr 2019 12:30PM
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A genuine question here, but do you get a better density of pour foam if its trapped? I have injected it into holes before to stick a layer back down, but I don't think I have seen what the density is afterwards as I haven't cut it up.

Left in the open I have no doubt that it creates the voids that Mark suggests.

decrepit
WA, 9108 posts
23 Apr 2019 2:40PM
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Yep, I usually try and get some compression. My foam is ancient, (GP 330) I don't use it a lot, I keep expecting it to be hard when I do use it, at a guess it's about 25/30kg/m3 when poured under compression. I've just found an off cut from the last time I used it.


So as Mark Says, it's soft and full of holes.
Funnily enough sometimes Australia is different to America.
So I guess it depends where gofaster is, if in Aus don't use this stuff for critical repairs.

Mark _australia
WA, 19092 posts
23 Apr 2019 2:43PM
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The density quoted is always "free rise density" for that reason, 'nova

Contained it is much better but as you said then you never know just how good.

gofaster
87 posts
23 Apr 2019 5:26PM
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Today I cut out the bad eps and glued in blocks of foam with gorilla glue, then sanding flush.Worked well. The overall surface is not completely smooth though.Does it need to be?If it should would q cells in epoxy be ok here?
2nd question; on the board lady site , she shows skarfing the exsiting pvc then glueing in the repair pvc with a glass patch wrapped around/under it.Is this the go? Doesn't seem to shape the bottom of the patch either.No need to?

decrepit
WA, 9108 posts
23 Apr 2019 7:02PM
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There's 2 approaches here, board ladies is the easiest, but you need plenty of pressure to form the new PVC over the old skarf.

If you have a router, you can set it to a fraction less than the old pvc, and remove a 2cm wide strip around the perimeter of the damaged area. If you get it right, this leaves the underlying cloth intact. You can then butt the new pvc with new underlying cloth up against the old.

Both ways provide continuity between the new and old underlying cloth, that's the important bit.

forceten
654 posts
23 Apr 2019 9:26PM
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Quite a few more than 2 approaches. Those all being presented , are sound and can be done at home. Cost will vary depending on what is on hand VS what needs to be purchased.

Im not a chemist, nor NASA scientist. I use what works for me.
dalchem.com.au/product/polyurethane-foam/gpf96-high-density-rigid-foam-kit.html

This pour foam product, shows 96kg/m3, which converts to 5.99 lbs density.

decrepit
WA, 9108 posts
23 Apr 2019 10:01PM
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Select to expand quote
forceten said.. dalchem.com.au/product/polyurethane-foam/gpf96-high-density-rigid-foam-kit.html
This pour foam product, shows 96kg/m3, which converts to 5.99 lbs density.


That looks interesting, thanks for that. Very heavy though, wouldn't want to use too much of it. But seeing the pvc we use is 80kg/m3, it could well be used as part of a sandwhich.


Select to expand quote
forceten said..
Quite a few more than 2 approaches.


Yes obviously.
Guess I should have quoted what I was replying to. That was the board ladies approach of skarfing the pvc, the other method is an underlying cloth overlap and a pvc butt joint.

forceten
654 posts
24 Apr 2019 9:43PM
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Select to expand quote
FormulaNova said..
A genuine question here, but do you get a better density of pour foam if its trapped? I have injected it into holes before to stick a layer back down, but I don't think I have seen what the density is afterwards as I haven't cut it up.

Left in the open I have no doubt that it creates the voids that Mark suggests.


Pour foam.expands a lot, 30-50%. Once it's set it has to have layers on top ,as glass , carbon so small imperfections are insignificant. It doesn't destroy the EPS , and epoxy adheres to it nicely.
I have never injected it. No comment as that to me is a non desire able fix.

i find pour foam works well for me, it's easy to use , sand , it takes the shape of the cavity.it floats and doesn't take on water.





gofaster
87 posts
27 Apr 2019 4:37PM
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Went to buy carbon cloth - faced with lots of different ones. What should I be using for this repair?

decrepit
WA, 9108 posts
27 Apr 2019 5:34PM
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There's a very thin broad close weave that looks fantastic, STAY away from it! I used some like that and it wouldn't wet out, it was designed for resin infusion.
There's not much 3D shape there, so a straight ordinary 50/50 simple weave around 200gm/m2 should be fine, or go with the cheapest. Carbon often comes in different widths, so take that into account as well.

Mark _australia
WA, 19092 posts
28 Apr 2019 9:54PM
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200gsm twill or satin weave.
Drapes (bends) better than plain weave and is stronger. Conventional, easy.

But like decrepit said, there is not much curve there, and different widths are cheaper, and the strength difference is negligible..... so who cares.
If not in a hurry, look for 300mm wide chinese crap on eBay it will be $10 ish.......... not the $80 that some aussie shop wants to sting you.

olskool
QLD, 1273 posts
29 Apr 2019 6:02AM
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I bought 200gsm twill carbon recently. 1m x 1.2m . $40. Perfectly matched a Severne mast i was repairing.



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