west system on seams??? please help!!

[randallt]

i have a venetian gondola and i am having new compound put in the seams. i have been using boat life caulk(as was recommended to me on here). most of the bottom seams are finished with this. the guy who is doing the seams is also painting the sides. he says the paint will not stick well to the life caulk. he scared the hell out of me because he wants me to get west system 407 low density filler, 105 resin, and 205 hardner, for the above the waterline seams. i have read a lot of threads on here and this does not sound right to me at all!! am i right on this?? also, is his assessment of the paint/boat life caulk right?? if so is there something that is more painter friendly?? for the record this guy is a GREAT worker, and is great with fiberglass. he is no wood boat expert though. we have a language barrier, but i think he may be getting bad advice from someone he knows. i really appreciate any advice and if any of you are ever in houston stop by for a ride!! thanks, randall

[Stan Derelian]

NOOOOOO!!!! You do not want to use that in the seams!!! There are a lot of opinions on that, but they seem to divide into two camps...The goop group who advocate compounds like polysulfides, and the other who go with the traditional materials like red lead putty, interlux seam compound, etc.
Do some searches in the archives. You'll will find more than you can believe...I know. I asked a similar question about a year ago.

[Bob Cleek]

Sheesh! Yea, he sounds like a lotta guys who know how to paint fibreglass, but don't know squat about painting wood. He is right that paint won't stick to the LifeCaulk worth a darn. I've had it work, but it isn't reliable and light color paints also will discolor over it.

The LAST thing you want to put in planked seams is a rigid, hard, compound like epoxy! JEEZUS! Imagine what happens to your caulking seams when the planks swell as they are supposed to do, but the epoxy stays hard... your instincts are right.

As I recall, you have a real, honest to God Venitian built gondola. Now, I can't imagine why you would put ANYTHING on it that wasn't "stock" from the factory. Those guys have been building those boats for hundreds of years and pretty much have a "mature technology" there. I'd expect they use a rather mundane white lead putty in those seams. That will take paint well, stay flexible for quite some time, is dirt cheap, MUCH easier to work with than polymer sealants, and is true to the classic original craft she is. Why not call the maker and find out what they used in those seams to begin with. You might also try finding a boat painter next time, instead of some guy "with a language problem" who learned to paint in a Tiajuana body shop! LOL

[randallt]

thanks fellows. i was pretty sure about that but wanted to make sure of it!! the builder recommended interlux compound, or boat life caulk. do you know if the interlux is more compatible with paint??
my amigo does great BOAT work but just knows nothing about wood boats. he just finished up a 32' fiberglass gondola that i have. sprayed it inside and out with awl grip...did the bottom job...and all the prep work. had a week turn-around on it, and it came out beautiful! cost me $600 total(materials and all!). i just need to get him dialed in on the wood side of it!! thanks for the input. randall

[randallt]

actually....i made a mistake. the builder recommended boat life caulk or "3m seam compound"...would that be the 4000 or 101 or other?? what about its paintability??

[Dan McCosh]

Hate to wade in as a contrarian, but the use of the polysulphide below the waterline and epoxy/lighweight filler above is what I've used successfully for years. There is no question about not using a hard compound below the waterline, but the topsides were caulked in 1936 with white lead compound, which sets up very hard. I used various kinds of filler for years, but about four years ago started using West and ultralight filler. The latter is a lightweight thermoplastic that sets up with some flexibility and is actually less dense than the mahogany planking, hence doesn't crush the plank edges. It has a low softening temperature, which in hot weather make it a little softer and flexible. The hull is painted dark green, which causes it to soften on a hot day. When the planking dries in the sun, it tends to give rather than crack, then hardens again when cool. It's a considerably different material than the hard epoxy fillers. All in all, it works great. (the filler is the 410 ultralight)

[ 04-11-2003, 05:55 PM: Message edited by: Dan McCosh ]

[paul oman]

Hello:

There are epoxies with 100% elongations, etc that can be thickened into a flexible epoxy putty.. These are epoxies are used, outside the marine industry, for cracks and cuts in cement, etc. I've also used it as a flexible epoxy non-skid (with grit added) deck system.

paul oman
www.epoxyproducts.com/marine.html (http://www.epoxyproducts.com/marine.html)

[thechemist]

Epoxy product should not be used in seams because they do not allow enough shear movement or compression/expansion of the planks on each side of the seam. Even white lead, set-up hard, is not a strong adhesive and the planks can move if need be.

Wood only has a shear strength of 100-300 pounds per square inch [psi]. Epoxy-merchants will tell you how strong their product is, and what high-bond-strength may be obtained [in bond-strength tests designed to avoid the real-world shear-strength limits of real wood]. Even products with elongations of 100% or more may have a modulus of elasticity [how much force is required to get some elongation] high enough that the shear strength of the wood will be exceeded with a small increment of displacement.

The wood will move.

The issue is not the strength or possible elongation of a glue or sealant in the seams, but how much force is required to obtain that elongation. In other words, when an inevitable displacement/elongation happens, how much stress is placed on the wood where the sealant is stuck?

Sealants must accomodate that relative displacement of one piece of wood relative to another without causing the shear stress at the sealant-wood interface to exceed the shear strength of the wood, and that means of wood as moist as it will be in real-world service.

The Gougeons popularized epoxy products for amateur marine use about 35 years ago, and through adequate start-up financing and brilliant marketing convinced a large segment of society that just about every part of any boat ought to be West-System-epoxied to each other.

In the ensuing years many other small businesses have started up, offering a variety of formulated or repackaged epoxy products [nowadays often called "Googe" in honor of those who went first] for similar applications.

The false data originally disseminated by the Gougeons has become repeated so often that it has been picked up by other businesses and promoted as fact.

Take, for example, a seam 1/8" wide, which through natural flexing of the boat structure in the water moves ten percent apart or fifteen percent in shear. What if it takes 100 pounds per square inch of seam-cross-section-against-the-wood to stretch the Stretchy-Googe(tm) that much? The wood will likely fail at some microscopically small spot where there were a few weak fibers, and then the Stretchy-Googe begins to peel. Peel strength of Things-On-Wood is measured in tens of pounds per lineal inch, and one thereby develops "Zipper-cracks" [Danenberg speaks of this in how new book.It's worth getting: http://media5.hypernet.com/cgi-bin/UBB/ultimatebb.cgi?ubb=get_topic&f=1&t=006519&p= ]

Wood, being a natural substance, has weak spots where the fibers are not well-attached to each other. Seam sealants need to have high elongation at very low elastic modulus, to keep the stress at the wood adhesive interface WELL BELOW 100psi, or allow slippage as many seam compounds do. percentage elongation numbers mean nothing. Only the elastic modulus number is meaningful in this regard. You want numbers comparable to 2-part polysulfides or urethanes such as 3M 4200, for a REALLY soft, stretchy product. There simply are no commercially available epoxy products that offer an elastic modulus this low.

The reason such epoxy products do not exist in the commercial marketplace has to do with the size of the molecules required to make molecular coiled springs that stretch easily. If one were to formulate such products, they would be either viscous, unworkable tars or have to exist in solvent solution. They just cannot be made with many small molecules that, before curing, are low-viscosity liquids.

[thechemist]

And another thing: It is easy to mix an epoxy 2-part system off-ratio [or for a formulator to make a 2-part system, even one-to-one-by-volume, which is inherently formulated off-ratio, meaning that perhaps only one out of every two or three amine groups are reacted with an epoxide group.

Such products will be very flexible.

They also will have high moisture absorption, and mechanical properties [as well as adhesion] will change drastically when tested after immersion sufficient to give that weight-gain.

A product which has adequate mechanical properties in a non-immersed application will not necessarily have decent or even useful properties in immersion-service. See what the manufacturer recommends for their product, and see what tests were done to back up the claims.

[Dan McCosh]

This is an interesting analysis, but movement of 10% in sheer along a seam line would indicate the fastenings have given way, and the boat is in danger of disintegrating. Lots of boats have been built with glued seams, splined seams, etc., and are very successful as long as excessive shrinking or drying don't occur. Main problem is shrinking across the grain, which puts a tensile load on the seam, when the planking dries out. Using a srong epoxy adhesive here would in all likelihood tear out the edge of the plank. I have seen glued-seam boats split a plank down the middle. The 410 filler is not particularly strong, however, (not recommended for any glueing application) but has enough internal strength to avoid crumbling out of the topsides, which is the usual failure mode of dried topside compounds. When the planks shrink enough to cause the seam to pull apart, the compound cracks. If a reasonable moisture content is maintained, it holds up quite well. In practice, the older planking moves quite a bit more than new planks. In the new wood, it stays solid even when the boat is hauled and dries.

[randallt]

wow...thanks for all the info! i actually put it to good use, i think. after putting all the info together we just went ahead and put 5200 in all the seams, and glassed over them and the whole boat........JUST JOKING!!!!...DON'T LYNCH ME!!..actually, everything below the waterline is boat life life caulk, and we went with interlux seam compound on everything above the waterline. hopefully this will work out good. thanks again for all the advice! randall

[thechemist]

Originally posted by Dan McCosh:
This is an interesting analysis, but movement of 10% in sheer along a seam line would indicate the fastenings have given way, and the boat is in danger of disintegrating. <snip>Not necessarily, Dan. It depends on what you mean by "ten percent". Planks resting tightly against each other, with only a few thousandths of an inch of seam compound separating them, might slide a thousandth of an inch, and this movement be normal. Planks an eighth of an inch apart, meaning an eighth-inch-wide seam, might move ten percent of that, or .012 inches, and I agree that there is a slightly loose fastener or two in that area, perhaps at the butt end of a plank.

[Leon Steyns]

Maybe you should contact Thom Price, he's certainly an expert on Gondolas and he speaks English... smile.gif

http://www.squero.com/

There's even a Gondola Society... :eek:

http://www.gondolanetwork.com/

Greets, Leon Steyns.

[randallt]

thom is the one that told me about this forum, and i am an active member of the gondola society of america. thanks anyways for the info. randall