West System...Brittle?

[Leon m]

I just ran a test on a strip of 3/8 ply
useing West 207 hardener .I was very surprized
at how easy it was to crack(epoxy not wood)
by bending the board against the corner of my
workbench.

I was considering using 207 to clear coat my
sharpie,wich I suspect will have some flex in
the hull because its a long narrow boat.I'm
conserned its going to crack.I will be using
4 oz.Glass,will the glass help ...a little,
a lot , or should I use a more flexable epoxy?
If so what would produce a nice clear coat ?

Thanks...Leon

[ 05-25-2003, 11:31 PM: Message edited by: Leon m ]

[Todd Bradshaw]

There have been plenty of strip canoes built with 105/207 and they seem to flex without the resin cracking, so I wouldn't worry about it. Some resins do have more flex, but if the plywood is flexing that much it would seem to me that the scantlings need to be beefed-up, rather than a different brand of resin substituted.

Maybe I'm out of touch, but what raised an eyebrow here was using a single layer of 4 oz. cloth on a sharpie and expecting it to do much of anything in the first place. I've always thought of it more as something to use on paddles or ultralight racing hulls. As far as I've seen, it doesn't have enough body to make any kind of serious contribution to the hull's strength or abrasion resistance and if the boat was fir ply I'm not even sure it's got enough beef to stop it from checking.

If you will take a chunk of four-ounce cloth, saturate it with resin and squeegee it out on a piece of waxed paper or polyethylene, let it cure, add a couple filler coats, let that cure and then peel it off of the paper, you'll see just how thin and flexible it really is - and how little it's going to add to the boat in terms of strength or durability. It just seems to me that if you are going to go to the trouble and expense of fiberglassing over a plywood hull, you might as well get something out of it.

[Ian McColgin]

Most epoxies are fairly brittle as big glops. If you make a puddle of WEST on wax paper and then bend the cured thing, its breakage is almost explosive. Yet on a thin glue line, it has good flexability. The googe bros made the beams to the amas on a racing tri essentially a laminated wooden spring and it appears to work well with no apparant limit to its cycle life.

Similarly, epoxy properly saturating a flassfibre matrix does not appear overly brittle.

Epoxy fillets are quite rigid and if they fail, they fail as a crack.

Some epoxy sealers (not meant for structural gluing) like (my fav) Glovit are actually flexable. Mix a bit and let it harden in a dixie cup and you get something that will bounce. I like the way it works with glass cloth.

I had horrid problems for years with Goblin's leaky coach roof. A prior owner had glassed it but the whole boat wracked so much on a beat that it basicly tore off and floated above the wood. I eventually 'solved' the problem by pouring liquid lifecaulk into all the seams and then putting down a sealer coat of gluvit - regular deck paint with sand over that. So, sometimes flexability does help.

Mr. Smith claims that his epoxy wonderfully matches the ductility of wood and he makes lovely products, both sealers and glues, but I'm not personally sold on the flexability bit. Seems to me than any gloop applied too thickly is bad practice.

By the way, I'm a great believer in getting to know a product and I'm not a real epoxy chemist, so I've pretty much stuck with WEST and Gluvit for the last 30 years. Have happily used CPES in its place as a thin penetrating sealer. I don't really doubt the other propriatary products. Just not used to them.

G'luck.

[ 05-23-2003, 09:44 AM: Message edited by: Ian McColgin ]

[Scott Rosen]

I don't like using epoxy for a clear-coat. It doesn't have the necessary UV protection. Even if you overcoat it with a couple of coats of varnish, the epoxy still represents a weak point in the finish.

The best bullet-proof clear finishes are the two-pack linear polyurathanes. They are designed to stand up to the sun, and they have more flex than epoxy.

Smith & Co. makes one called FiveYear Clear, which I've never used, but which got Practical Sailor's highest rating.

Sterling makes a clear LPU. So does Interlux. I imagine they're all pretty good.

[Wild Wassa]

Australian sunlight is very intense, uncoated epoxy wont last a full season (6 months) over here. It becomes overly brittle, looses it's adherance and starts to break up and peel. With a few water based poly topcoats, after two seasons, the paint still looks brand new.

Paints with more pigments, or opaque pigments, give better protection against the UV.

Warren.

ps, we have a big hole in our ozone layer, ... sitting over my local lake.

[ 05-23-2003, 06:32 PM: Message edited by: Wild Wassa ]

[Leon m]

Good advice ! Maybe if I give you a little
more detail it will help.the plywood Im useing
is african mahogany marine ply 3/8 thick with
a 20 year guarantee(nice stuff).Most of it
will be bright finished,I was told that if
I glass it and go over it with UV farnish
it should hold up pretty good(?)but some say
otherwise :confused:

Todd : what wight glass would you recommend?
the boat should be rigid but I do expect to
sail in rocky areas.

Ian: glovit(Im not familiar) tell me more.

Scott: what about UV varnish over apoxy?

Wild Wassa :Here in Wisconsin it doesn't
get too hot so I hope I'll be OK.

[ 05-23-2003, 11:46 PM: Message edited by: Leon m ]

[Todd Bradshaw]

I don't know the particulars of the boat, but if you're adding fiberglass cloth to improve the abrasion resistance or general hit-a-rock-type durability of 3/8" marine plywood, I would think it would take a minimum of ten to fifteen ounces worth of fabric or fabric layers to notice any real improvement over just resin coating the ply. Resin is fairly hard though, and with or without the cloth it's probably going to resist gouging and deep scratches somewhat better than just paint.

If you're adding fiberglass cloth (to one side of the hull only) in hopes of stiffening the hull, I wouldn't be surprised if it took 30 ounces or more of fabric to make much difference. In either case, you're about at the point where the cloth weight may start to seriously hamper trying to get a nice, bright finish. There certainly may be a just case for taping the outside of the chine seams to protect the end grain of the ply, but to do it right would probably take at least a couple layers of 7.5 oz. or similar tape, which may not come out perfectly clear.

I would probably either resin coat the plywood (without the fiberglass cloth) to get a better bright finish, or fiberglass the bottom, chine seams and maybe up to the waterline with a fairly substantial layer of glass, then paint that part of the hull and have coated, non-glassed bright-finished stuff above the waterline.

If the boat is covered when it's not being used, it should hold-up pretty well around here. My Star had six thin coats of 105/207 rolled over it's alcohol-stained, mahogany-veneered topsides. Then I sanded it smooth and put on a couple coats of Captain's Varnish. It sat outside for two years in Illinois and five here my driveway in Madison under a Sunbrella cover and still looked great. Don't try it without the cover though. If the boat will sit out uncovered or sit out on a mooring you almost have to paint it if you want the epoxy to last more than a season.

[paul oman]

We sell a number of marine epoxies and have tested many of the other brands. They all have different levels of brittleness (based upon the sledge hammer test!). We reformulated our Basic No Blush epoxy about 6 months ago to make it less brittle. Yes, I've found West to be a very brittle epoxy based upon my tests. How can you tell? I think you have to test them against each other and find someone that has done so and will talk about it.

Paul Oman
progressive epoxy polymers
www.epoxyproducts.com/marine.html (http://www.epoxyproducts.com/marine.html)

[Todd Bradshaw]

So it's safe to conclude that if one intends to hit his boat with a sledge hammer, WEST may not be the best choice. Unfortunately, the test is just about as meaningless in the world of real boatbuilding as it sounds.

Leon, if you'll wander out onto the ice on Lakes Kegonsa, Monona or Mendota on a winter Saturday afternoon you might see the fleets of iceboats racing. Almost all of them are home-built and about 90% of them from wood and WEST epoxy. In use, their parts are under tremendous loads, flex like crazy and are sometimes subected to teeth-jarring vibration for an entire weekend's racing.

Some of the Skeeters are worth upwards of $20,000 and no expense is spared in the quest to build a faster, stronger boat. If there were brittleness problems, or if the WEST Epoxy offered anything other than excellent strength and performance, those guys wouldn't be using it. It's certainly tough enough to help reinforce a sharpie that might occasionally hit a rock or get dragged up on a beach.

There are several really good epoxies on the market. They do have somewhat different working characteristics and you may eventually find one in particular that you like to work with more than the others. You might save some money as well as WEST sells for a premium price. In the mean time it is as good a place to start as any of the others and until boats start shattering (which hasn't happened yet) the brittleness claims don't seem to hold water in real day-to-day life.

[George Roberts]

Leon m ---

You might look at Dave Gerr's book Boat Strength to determine how much plywood and glass he thinks you should use.

I don't know your needs but if you think you need to add glass you might get buy with thinner plywood.

(I will try to stay out of the discussion of various epoxies.)

[Leon m]

Originally posted by Todd Bradshaw:
Leon, if you'll wander out onto the ice on Lakes Kegonsa, Monona or Mendota on a winter Saturday afternoon you might see the fleets of iceboats racing. Almost all of them are home-built and about 90% of them from wood and WEST epoxy. In use, their parts are under tremendous loads, flex like crazy and are sometimes subected to teeth-jarring vibration for an entire weekend's racing.

Thanks Todd !thats the kinda stuff I was hoping to here. Oh! and thanks for the education on
trailers in the other thread ,I think I have found
one ,I'll be talking with the owner on tuesday.

Paul, you have any sample (test)kits?

George, Thanks for the tip I'll give Dave
Gerrs book a look.I'm starting to get real confused about what weight of glass to use.
the plans for my boat call for paint only
but I really want to use glass for a number of
reasons.I'm going to stick with the 3/8 ply
because the hull is already built ;)
Sam Devlin says use 4 or 5 oz. others
say use 9 and up :confused: :confused:

[paladin]

Please note the above.....The predominate area and climate where the ice boats are used izz COLD. From a lot of experience in the TROPICS W.E.S.T. epoxies have a reputation for turning brittle after 2-5 years......But then again...most of the boats that I am familiar with were well primed and painted a light color...dark colors mean more heat and a faster breakdown...

[thechemist]

Originally posted by paladin:
Please note the above.....The predominate area and climate where the ice boats are used izz COLD. From a lot of experience in the TROPICS W.E.S.T. epoxies have a reputation for turning brittle after 2-5 years......But then again...most of the boats that I am familiar with were well primed and painted a light color...dark colors mean more heat and a faster breakdown...The reason for that is the evaporation of the non-reactive plasticizer benzyl alcohol that is in the WEST system products.

Evaporation happens faster in hotter weather.

[George Roberts]

Leon M ---

If you just want to waterproof the plywood, then 4oz glass will provide a uniform .006-.010" thickness of epoxy. Just about right.

[Todd Bradshaw]

George raises a good point that doesn't get mentioned often. A layer of fiberglass cloth does sometimes act as a "thickness control", for lack of a better word. It can help both in terms of being an aid during resin application, helping you make sure you have enough thickness in your sealer coats to do the job properly and also during any sanding or fairing on the cured surface. If you start to see little whitish spots where you are down deep enough to hit the cloth, stop sanding in order to maintain proper thickness.

You don't need a lot of heavy weight fabric to do the job but keep in mind that a single layer of 4,5, or 6 oz. cloth which will work fine for thickness control is not going to do much at all in terms of beefing up the boat's structure or dramatically increasing it's impact or abrasion resistance.

[ 05-26-2003, 08:10 PM: Message edited by: Todd Bradshaw ]

[John Blazy]

Todd, I couldn't agree with you more on thick where you need it and thin where you don't. I am planning on laying 38 oz of a heavy biaxial weave/csm combo onto the bottom of my 14 footer tonight and laying in a strip of lam-bent oak as a 'keelson' or sacrificial rub keel into the wet glass/epoxy of this boat below in which I already glassed the sides using 4oz glass in WEST 105/207 pressed in with 30 mil polyester film/sheet:
http://www.imagestation.com/picture/sraid62/p89fa59a0d77ca91d5ae21f7ecb347128/fc1b6462.jpg
By rolling the polyester film into the wet glass, I eliminate hours of fairing, and I compress the weave flat against the plywood, so it doesn't "float" to the surface, susceptible to being sanded off. I just scuff the surface after peeling the film off and varnish - should look like glass - the way you see it here.
I am leaving the film on now to protect the sides against drips when I heavy glass the bottom panels. I plan to go near rocks, so I need all the glass thickness I can get on this bottom. - JB

[Leon m]

John B
That sounds like a real good plan 38 oz
on bottom and 4 oz on the side.I love the polyester film idea...where can I learn more.

and to all the rest... THANKS ! your
really helping me out.

[Todd Bradshaw]

There was also an interesting article which looked at some older epoxy-constructed boats and how various parts and building methods were holding up over time in issue 17 of "Epoxyworks" (Gougeon Bros.) magazine. You can read it on-line at:
http://westsystem.com/ewmag/17/index17.html

Scroll down to the article on wood/epoxy longevity

[John Blazy]

Great link Todd. Beautiful boats too. Leon, you can learn more about my polyester film idea by clicking onto the thread I posted recently called "'nuther brain teaser forya". Scroll down the topic list - its still on page one.