Composite compression

Hypothetical question…

Say one were actually to do the impossible.  To able to make  2 identical Fin panels, same amount of layers of cloth. Laminated exactly the same.  No variables.

 

One panel is left to dry unmolested after the final layer is wetted/rolled, squeegeed ect, the other panel gets another piece of waxed glass placed atop it and  is perfectly and evenly compressed with a significant amount of weight, to the point it squeezes out some extra resin which is allowed to run off, and this panel becomes thinner and the resin then cures under this compression.

 

So these two theoretical panels have the same amount of fiberglass.  Say One panel winds up being 5/32"  thick, the other is 1/4"  thick.

 

Which Fin panel is going to be stronger?  5/32 or 1/4"?

 

Which will flex more before breaking?

 

Which will flex more under the same applied pressure?

 

 

George Greenough did a lot of that in mid-late 1960’s. I think both over all stronger and snappier flex was the result. As well of course as lighter. He made mold of rough fin shape, filled w/ fiberglass roving, all going same direction, then backed car up on top of it for lots of pressure.

Most fin panels are made with a good roller to apply the pressure, and if done properly, will not have any disadvantages to a pressured panel. 

Resin types, hardeners, fabric type, layup schedule, curing and post curing would be more influential on the final product.

I used a fin panel only as an example where one could eliminate many of the variables and compare the possible differences in results with the only difference being the compression of the composite.

 I am not making fin panels.

 

Recently I stumbled on a ‘new to me’ technique of fixing dings and was going to keep it to myself in ‘secret sauce’ fashion, but heck with that, I’ve learned too much here to not return something possibly helpful to others.

 

Basically, I got some serious rail dings recently. Granite wins again.  I sanded through hot coat to original fiberglass below and a little more. Confined the ding with blue tape. Sand to edge of tape. Standard ding repair stuff.

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I used a 5.5oz Carbon fiber oval covered with a bigger oval of 3.7oz E cloth Oz covered by a bigger oval of 1.43 oz veiling cloth.  Yes the carbon is unnecessary, but I’ve enjoyed its ability to bridge ‘soft spots’ under the shell.

 

I used a ‘wet out table’, saturated all 3 layers together, gravity style, squeeegeed out obvious excess, lifted all three  and lightly squeegeed layers into place,  to the rail profile.

 

But then, I used a large  thicker Ziplock brand  baggie  cut open for a single layer and pulled it tight over the rail profile, and worked out the bubbles and extra epoxy with a finger  from center to the blue tape edging, and no further.  Then, instead of a finger, I tried  a stiff well rounded dry squeegee and Pushed  on the plastic working extra epoxy from center to edges while pulling tight on the plastic with other hand.  I was surprised at how much pressure I could use and how much compression I could achieve and no white spots/dry spots with the plastic preventing air intrusion behind squeegee.  I was also surprised at how much epoxy I was able to squeeze out from patches I had already squeegeed on the wet out table of seemingly all excess resin.

 

As the epoxy slowly thickened it got harder to push the epoxy out to the tape, but the 3 layers of fabric got greatly compressed, and pulled as tightly as possible and had no tendency to pull back/suck back in the extra epoxy.    The carbon edges actually squeezed out and look like they were cut by a toddler with safety scissors, but Oh well. This particular board is no looker anyway.

With the plastic, the pressure one could apply pushing, was several fold more times more pressure than one could use had there not been plastic between cloth and squeegee.   Using the reflection of the light on the plastic I was able to basically mold the epoxy and layers of fiberglass and CF nearly perfectly to the shape of the rail, without any obvious bulge or edge where one layer of material would end.

After I have pushed the layers as flat as possible with all epoxy pushed to the blue tape and no further, I run a new  razor blade lightly inside the tape line, and remove tape and extra plastic outside the tape with it.  In a few hours I can pull the plastic and have a perfectly glossed repair which requires little or no sanding,  and no more epoxy.

I am wondering if these 3 layers of highly compressed fabric have the same strength as if I had done a traditional fix, where each layer was able to absorb all it wanted and excess squeegeed out then feathered edges then re hotcoated then sanded flush and smooth.  I hypothesize that  the traditional method would be thicker and therefore have greater strength compared to being compressed and thinner.

 

But, since there is no more sanding required, and there are the same amount of resin saturated fibers, perhaps it is stronger?  It certainly has to be lighter.

 

Basically there has to be a downside of this simplicity right?  This technique of fixing rail dings certainly saves many steps and lessens waste, but it is weaker than  the traditional method?

 

To others trying this squeeging the plastic method, the thickness of the plastic is fairly key to prevent stretching and creases when Squeegeed.  I use the thicker white squeegeee, about 3 inches wide with very rounded edges.  The Ziplock freezer bags worked far better than regular ziplocks which would stretch and crease too much, I will be researching better plastic for this task, at least for rail dings.

 

On one larger ding the bag was not big enough.  I used two bags.  Where the two bags overlapped I could not pull the cloth as tight, squeeze out the excess and the result was less stellar requiring sanding and a fill coat.

 

I am thinking there are other applications, such as compressing the edges of laps and possibly eliminating the need for a fill coat, or reducing it greatly, By doing a whole side of the board using this method.

 

With the right plastic, I imagine it could be reused many times too. On one ding I did not razor the plastic inside the tape and was able to reuse the same baggie again.

 

I know the vaccuum bag guys are achieving something similar, but squeegeeing this thicker plastic over the lamination method allows one to pull the fabric as tightly as possible, squeeze out all extra resin, compress the fabric to an impressive degree, and there is no fill coat required, and no vaccum pump, or peel ply, and it is relatively simple and pretty hard to screw up, with the consequences for screwing up, so far, as far as i know at this point, just being some sanding required afterwards, instead of the pull plastic go surfing methodology if it does come out acceptably well.

 

I’ve no experience vaccuum bagging, but see many possibilities with this squeeging the plastic method, as long as I am not sacrificing strength by the compression of the layers.

 

So I come here to ask those with much more experience and knowledge in this matter.  What are the repercussions of this untraditional approach?

 

Any light bulbs going off, or have I been smoking crack and drinking the Kool aid too long?

 

I’ve done similar technique.  Try getting some ‘Stretchlon’ material.  It can be pulled pretty tight and because it’s stretchy, you can usually pull any wrinkles out.

Can’t say it’s significantly stronger but as you’ve noticed, it can save a fill-coat step.  I still end up feathering the edges, exposing weave, glossing, etc. but the initial lamination comes out smoother and the glass is compacted a bit more than convential lamination.

If you want to try some, PM me and I’ll mail you a piece.  Or just buy some from Fiberglass Supply or someplace that sells vacuum bagging stuff.

Thank you, I will look into the stretchalon material.

 The Zip lock freezer bags do not really stretch that much, but the thinner regular zip locks did, and the results when squeegeed were not as good.  I think there might be a fine line of stretch vs durability when the squeege is pressed down 5 to 10 times harder than one would use laminating regularly.

 

I was very surprised at just how much pressure I could use and not visibly starve the fiberglass of resin.

 

With the squeegee and some time and effort expended during the thickening stage, I am not seeing any personal need for feathering any edges as one can mold the slowly hardening epoxy to fill the edges where the cloth strands end.  But I am not seeking a perfectly invisible repair either, only fixing to watertight and calling it macaroni. But with this method am achieving results much better than I really require for my personal needs on personal board repairs.

 

I love just pulling the plastic and not having to sand any farther or mix more epoxy.  I spend extra time molding the laminations to rail shape with squeegee ontop of plastic, but later save a bunch of time as cutting the plastic and pulling the tape can be the final step and the result, perhaps better. 

 

Perhaps something similar to this technique can be used to save time in regular layups and reduce waste with a possibly better stronger  lighter result.

 

I think a slippier dry squeegee  on the plastic could also improve results or reduce time it takes to push out excess resin and work out any bubbles.

 

perhaps some car wax applied to the plastic’s exterior and dry squeegee to reduce friction.

 

Almost hoping for more dings to repair to try and further improve this technique…

Asking interested members here to try this technique on a rail ding and tell me what you think. Squeegee the plastic laid atop the wetted fabric.  use a lot of pressure  on the squeegee and push out the extra resin from middle to edges pushing the cloth as tightly as possible to the sanded ding area.  Use 5 times or more pressure than one would regularly use, and force out all extra resin onto the ding confining tape, then razor just inside the tape, and pull tape and excess plastic outside repair.  later pull plastic over the repair.  

Tell us what you think of the results.  if there is no compromise in strength or adhesion, I can, at this point, see nothing but upsides to this technique and perhaps it or something similar can be used  in regular production for better results with less waste.

 

Like around tails or wings or just laps, or perhaps the entire board.

 

Not sure about how well it would work with PE resin.  But epoxy just thickens slowly and allows one plenty of time to mold and shape under the plastic.

 

I am also not sure if this molding and shaping of the slowly hardening epoxy  with hard squeegee ontop of plastic, would possibly degrade its cured properties or adhesion to substrate.

 

In my case on this repair,  I am adhering Apex Epoxy to Silmar polyester resin that fully cured 19 years ago sanded to 80 grit.

 

 

 

 

 

 

 

 

Good work.  I’m always looking for a new tip for dings.

I’ve had good success by just taping the larger outer layer of glass around the perimeter and pulling it really tight against the ding on the rail. 3M 233 tape is essential. Then a small piece of clear plastic tape over it to gloss it up.

all the best

I have had good success with saran wrap, wax paper, and even shrink wrap.  I like to use the shrink wrap over wax paper to really squeeze it in, but only on the flats…  Wax paper wrinkles like crazy on rails.

This cheap hand pressure mold was a norm when i make my composite rc plane wings 20 years ago then i go with vacuum bag for better pressure répartition. Main problem with hard squegge method is you can really micro cracking fiber at cross of yarns.
Answer to first post, if fiber is not micro cracking and resin respect composit building rules, your compress panel will be lighter, it will flex more under same flexural forces, equally under tensil force, buckle first under compression force. It will flex more before break. Energy to break will be better and fatigue strengh too. Because of working mode, stiffness is the main characteristic of surfboard skin for strengh against breaking and denting.

Thanks for all the input.

Lemat… these possible Microcracks with this much pressure, Invisible even magified?

 

The one soft area under the worst ding is no more, it feels super strong and rigid and sounds more solid than the rest of the board when rapped with a knuckle.

 

I decided to take the sanding block to the one smaller ding which other wise looked  a ‘good enough’ level of finished once I removed the plastic, and the shiny depressions reveal a far from perfect gloss coat.

There was a very  very slight print through in one area where the 5.5oz (?) CF patch ended, and a much smaller print through  where the 3.7 oz  E Oval patch ended, but nothing like if I did not compress it under the plastic with a squeegee.

 

There were also a few bubbles I had not seen when working the squeegee on top of the plastic that left some voids in the pattern of the cloth…

 

I wound up wetsanding with only 220, feathering edges barely, and smearing on another coat of epoxy with a gloved finger, and the result it is far better than I really require.  Not like this is a show board or I am repairing boards for dollars.  With Eyes closed I cannot feel the bulges of the CF patches.  Previous dings where I just laid 4 OZ over a smaller CF oval patch, the thickness of the CF was, and is very obvious.

 

I’ll still be exploring this method further.

Further thoughts for a better result is I need to get more epoxy off the stacked lam on the wet out table, or just wet out the ovals on the surfboard rail itself, or wet out the ovals separately squeegeee separately, lift and set them separately.  They were too wet and I was able to push out way too much epoxy. and the CF under 2 layers of fiberglass still  walked outwards with Squeegee, looking unprofessional.

 

Also The squeegeeing of plastic can be done earlier when the epoxy has not started thickening. I was taking my time and this epoxy is pretty fast.  I think pushing it to the edge of the oval patch and then wait for it to thicken some, then feather the edges more withte squeegee, and touch the middle of the patches less or not at all once epoxy has thickened.  Perhaps the results once plastic is peeled from cured epoxy can be done almost perfectly.  I did not achieve this but I think with practice it could be possible.

 

I still wonder about laying some plastic over the deck and hull laps and pushing them flat rather than letting them swell and have to be sanded. I’ve had issues with lap clarity over HWS rails in the past. Part is being an Epoxy miser and using airated epoxy to wet the laps, but part has also been sanding perhaps a bit early to insure I get that best possible chemical bond.  Eliminate the sanding and not being an Epoxy miser could allow the wood clarity I desire.

 

Anyway, unless these plastic assisted compression repairs prove to be weak, I will be using this squeegee the plastic over the lam method on all rail dings from here on out. 

  One other thing to add, this  recently acquired Apex epoxy I am using, My third 1.5 gallon kit, is different from previous batches. The hardener is Clear, the result is an almost water white epoxy.  It does not fisheye nearly as badly as the previous batches with the more amber hardener, and its smell is less than before and slightly different.  I like it.  For 81 dollars I think it is pretty good stuff. If you have a choice between teh amber and clear hardener, and i was led to believe there was a choice in the store, go for the clear.

In an effort to reduce weight for fins I’ve been rollering each layer on a wetting out table before I add it, rolling just enough to get that crystal look before it goes clear, the result here under magnification is a open weave that connects with each layer, the actual fibres of the glass have set but the spaces in the weave don’t have resin. It’s certainly light and strong enough for the job.

Thinking it was smarter to not add resin and then try to remove it but I always vac at -80kpa. Too high for foam but it holds the layers tightly.

It looks and feels both smooth and textured, I’m certain it picks up a layer of water and might even help with the boundary layer because it holds its own layer of water to itself.

Close up shows every layer is perforated with thousands of holes. It’s the same echinacea I use on fins and panels like hydrofoils and handplanes.