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sheathing BRS 17 with Xynole - how much epoxy


sscoville

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Xynole takes approximately 0.32# of epoxy per sq ft to fill the weave sufficiently for finishing.  Epoxy weighs 8.8#/gal.  So one gallon of epoxy will fill about 8.8/0.32 = 27 sq ft of Xynole.  These numbers are from my own work so there may be other numbers that are slightly different.

Fairing will add some weight also.

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Tom's numbers sound a lot more exact than mine, which are summed up by simply saying....a lot! You can't believe how much epoxy that stuff sucks up, which btw, is not bad in my opinion. It doesn't go into a black hole....it's building up a durable surface.

Tom: Would you say the best way to apply this is to precoat and sand the hull, then apply the xynole or do it dry the first time? Either way, I'm guessing 3 to 4 coats to fill the weave prior to the fairing process.

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I am getting ready to order epoxy to sheath my hull with xynole.  I've never used Xynole.  Does anyone have a formula for determining how much epoxy it will take?

sscoville... What weight Xynole are you planning on using?

Tom...  I'm asking out of igorance of Xynole -  but I'm used to using/hearing numbers close to 50% / 50% ratio of glass to epoxy as being a good ratio for optimizing strength (including for s- and e-glass) so your experience is a real shocker.  Can you shed some light on the 'why' it apparently requires so much more resin than would expected for glass? 

If the Xynole were vac-bagged what would be your guess as to the resin/glass ratio that might be attainable.

If you've ever sheathed in Kevlar... what was your experience for that?

Just askin' (was considering Xynole as a possible alternative to Kevlar for the bottom)

Thanks a lot,

TomH

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I think Raka carries either 4oz or 6oz.  From what I've read, it takes so much because of all the space between the weave, not that the weave absorbs so much, but I'm not sure about this.  I think you basically have to build up the rest of the boat to make it even with the outside of the Xynole.

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Xynole is not at all like fiberglass cloth and can't be treated as such.  All that I have bought came from Defender Industries and they only had one weight.  Xynole is an open weave polyester cloth constructed of fuzzy fibers that do soak up a lot of epoxy.    Not that the fibers themselves may ingest epoxy but the weave does.  A thick coat of epoxy on the outside of a hull, particularly the bottom and to above the waterline, is a good thing for waterproofness.  I like that feature on any boat that can tolerate the extra weight and that's any other than a racing boat.

The main reason I like Xynole is its abrasion resistance.  In objective tests that I made some years ago, Xynole was over 6 times as resistant to abrasion as 10oz glass.  Both were coated with the necessary epoxy to fill the weave.  Part of the difference is that the Xynole is much thicker but even on a per-thickness basis, Xynole is about 2 1/5 times as resistant.

I much prefer to put cloth on dry and Xynole does this much better than fiberglass because of the open weave.  Don't ecpect to sand Xynole because it almost can't be done.

I don't use Kevlar because its admittedly fine properties have not been necessary of the boats I build.

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Both Xynole and Dynel are fabrics with elongation properties much higher then regular 'glass fabrics, more closely matching that of the resin system it's used in (epoxy). This means it will distort and return to it's original shape after the 'glass fibers of regular 'glass have begun to break. The results are two fold: first is, the covered piece has a uniform flexibility, with the two elements fairly well matched and second is, the improved abrasion resistance of these materials in the cured matrix.

With the exception of some not very well known and less understood building methods, these polyester or modified acrylic fabrics are used as abrasion protection only in the marine environment.  A light weight sheathing (relative) of Xynole or Dynel will impart little to no additional strength to a panel covered with it, much unlike conventional 'glass fabrics.

I would think you could bag the fabric to control the resin/fiber ratio, but I wouldn't want to speculate as to what would be an ideal one, nor if it would be as successful at its job, with less space within the fabric for resin.

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I forgot the fiber to resin ratio question.  In a glass and resin matrix, a high glass to resin ratio is desirable.  How high?  For home builts without pressure or vacuum, you will not be able to get too much glass fiber in there.  50% is not nearly high enough in glass for optimum strength.

With Xynole, this ratio is not a big issue.  As Paul said, we use Xynole for abrasion resistance and as a highly waterproof sheath, not for stiffness or strength.  Abrasion resistance could undoubtedly be increased by multiple layers vacuumed to a thinner thickness but I don't know if that is normally done.  One layer is enough for the kind of boats we build. 

For that matter, woven glass cloth doesn't add nearly as much stiffness as many think.

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Tom, I think a generally unaccounted element of these materials abrasion resistance is the elongation properties. It's accepted that the material is tough, set in epoxy, much more so then 'glass, but then again so are cotton fibers and other materials.

When you slow down things, within a abrasion "event" to the point where you can have a good look at what's going on, you'll see a fair amount of deflection and material elongation. The resin can take this and is one of the things we rely on epoxy. So one option is fairly stiff fabric to "harden" the sheathing or a material that has an elongation similar of the resin so fibers don't break and tear within the matrix as deflection and distortion occur. These are the very reasons biax is a better choice for strength concerns and Xynole/Dynel for abrasion resistance, this ability to match elongation or add stiffness to the cured resin.

It would be an interesting test to have cotton and other fibers, which can offer the interwoven "fluffy" environment for resin to flow into, compared side by side. I suspect West might have some data in this regard, but haven't ever seen it yet.

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Tom & PAR,

Thanks so much for the careful answers.

I'll have to look closer at Xynole and Dynel for bottom sheathing - but from what you've said it implies that the resin much be well matched in it's physical properties in order to get the expected abrasion resistance properties.

Back in the day, as they say, I switched from WEST brand to System Three as my general purpose epoxy because of some instances where WEST seemed to be too 'brittle' for my liking and was well pleased with the improvement.

What epoxy brand/product are you using for the Xynole/Dynel application?

Are there any brands you found to be more or less well suited to these fabrics?

Thanks again,

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Par, all of the synthetic materials I tested did better in abrasion than glass.  Did not test any natural fabrics like cotton and don't plan to but think it would be inferior to synthetic.  Most likely the elongation of synthetics do aid in abrasion resistance.  For what its worth, 18-8 biaxial glass did rather well in abrasion also but was the heaviest layup I tested at .46#/sq ft.  For applications where strength and stiffness are required, biaxial is my choice.  For heavier abrasion duty, I'd cover it with Xynole.

Our use in boatbuilding is not normally as critical as other industrial epoxy applications so most any that can be worked in our environments will be ok.  In general, I would prefer some flexibility in epoxies.  Certainly there should be enough flex that the fibers fail just before the epoxy matrix.  FRP is a two phase material like bamboo.  The epoxy matrix should distribute stress to the fibers uniformly so that the strongest material is taking the load rather than the matrix.

I've had good all round results with RAKA epoxy.  The epoxy Graham sells is good also.  I did have some cratering issues in coating with it though.  That is often a problem with epoxies and generally the culprit is never found.  Epoxies I have used are Fuller, WEST, Chem Tech, System 3, LBI, Fiberglass Coatings, MAS, RAKA, Progressive, Graham's as well a few others not remembered.  All worked well as glue and some are better than others for coating and sheathing.  RAKA is not quite as quick to wet out fabric as WEST but is good for my use, considering the 50% reduction in cost.  Cost does not make a lot of difference on a small job but can be significant when the boat calls for 30 gallons or more.  That's at least $1500 to use for something else, like a new tablesaw. :grin:

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Tom forgets that we stopped getting that medium hardener that had some cratering issues.

I did not forget.  I never knew that.  So my experience was an aberration.  Good news.  Problem, or non-problem, solved.  Graham often plays with my head by saying he told me something that I don't know.  Could not be my poor memory.  Nah :P

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