Glue for vacuum bagging

[Robert W. Long]

Hi:
I'm starting a lapstrake ply boat. The plans give optional garboard thickness of 1/2 or 3/8ths. After some thought, I ordered all 3/8ths for the hull. The wood looks fine to me[sapele] but is only 8.5 mm. Expected it to be 9
My question is what kind of glue to use to vacuum press 1/16th home made veneer on each side of garboards to get them near 1/2". I have experience sawing veneer and vacuum bagging, but no boat building except one stich and glue kayak kit. Seems like I read somewhere that epoxy is not recommended for vacuum bagging due to excess pressure. Maybe I should just build the boat with what I've got. Other guys seem to have used the 3/8ths throughout. Any ideas? P.S. what is the bilge we lurkers are warned to stay out of? thanks , Robert

[Todd Bradshaw]

Epoxy works great for vacuum-bagging. Gougeon Brothers even puts out a small booklet on the process.

[kc8pql]

Or you could use resorcinol, which is probably what they used to make the plywood.

[Bob Perkins]

Robert,

I did a ton on vacuum bagging with epoxy. You can see some pics in my imagestation site below.

Once you get use to it, it works very well.

Mix up epoxy and thicken it some so that it will stay in place and not run when you spread it. Not too stiff, not too runny (Soft peaks in cooking terms). Use a notched spreader with little tiny notches (West system sells a little plastic one for .99)

Spread a real even coat. Then vacuum clamp away. I got nice thin glue lines and the hull is solid. I've drilled a couple of holes so far and the laminations are tight.

The vacuum pressure is so even that there were no lumps or voids detectable.

It would be interesting to see vacuum bagging in lapstrake. I bet that will be difficult..

Good Luck,
Bob

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My Current project is at:
http://www.imagestation.com/album/?id=4291051329
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[John Blazy]

If the garboards are narrow, why not use some clamps every eight inches or so with 2x8,10's or other scrap as backing cauls. Then you can adjust pressure as you need, might be simpler, and no pressure fear with epoxy. Just thinking out loud - JB

[Todd Bradshaw]

...and it might be wise to do a little testing first. Sometimes the amount of stiffness gained can be a big surprise. You wouldn't want to get the garboard stock laminated and then find that it won't bend to fit the forms.

[Venchka]

The 1/2" or 3/8" garboards sound very much like Iain Oughtred's larger double enders-Ness or Caledonia yawl. Iain shows a stringer lenghtwise on the garboards if you use 3/8". The stringer is about 1"x1-1/2" (long dimension up) and divides the garboard in half athwartships. That might stiffen the garboards enough and be easier than adding a layer of veneer.

Sorry to hear about the 8.5mm plywood. I had the opposite experience-the 9mm plywood I ordered turned out to be 9.5mm.

Wayne
In the Swamp. :D

[Bruce Hooke]

One of the myths of vacuum bagging is that it exerts a lot of pressure in terms of pounds per square inch. It doesn't -- over a relatively small area it exerts MUCH less pressure than a c-clamp. I believe vacuum bagging exerts about 10-15 pounds per square inch depending on how good a vacuum you can get whereas a c-clamp can apply 2000 pounds of pressure. The big deal with vacuum bagging is that it exerts that pressure over every square inch of the surface, which of course is very hard to do with clamps -- both because it is hard to spread out the pressure of the c-clamps and because vacuum bagging is usually used for large surfaces that are hard to reach around with clamps.

Anyway, the point in all this is that epoxy is excellent for vacuum bagging because it does not need high clamping pressures. On the other hand Resorcinol is supposed to be clamped very hard, so I don't think it would be a good choice for vacuum bagging. Other glues work well for vacuum bagging if water resistance is not an issue, but that clearly does not apply here.

[Bruce Hooke]

By the way, I just re-read your post -- if you are worried that your plywood measures 0.335" (8.5 mm) instead of 0.375" (9.5 mm or 3/8") then I would stop worrying and start building! :D I would be VERY surprised if a 0.04" difference in thickness would matter in the slightest and furthermore unless my memory is way off plywood is normally slightly thinner than it's stated dimension because of the sanding process used to surface it. However, if you want to be absolutely certain that the thickness you have is OK you could check with the designer, if he is available.

[Bruce Hooke]

Originally posted by Robert W. Long:
P.S. what is the bilge we lurkers are warned to stay out of? thanks , RobertThat is the "Misc. Non-Boat Related" section, which frequently devolves into political mud-slinging and other "blood" sports! However, that section also contains some good discussions about sports, music and life in general, as well as what is by far the longest running thread on the forum -- the Humor thread (http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=5;t=003646), which has got 1753 replies on it and counting...

[JimConlin]

I've had good results using epoxy to bag veneers to thin plywood. I have a firm table, and use nylon window sreening as breather and neat Gougeon epoxy at approx 0.6 oz/ft^2. YMMV
I agree w/ Bruce's comment above re whether .04" is a relevant difference.
Build the boat!

[ 10-22-2004, 01:16 AM: Message edited by: JimConlin ]

[Cuyahoga Chuck]

.5 mm is only .020". If your ply has 5 verneers .020" shouldn't make a big difference. If you add some 'glass or Dynel to the bottom for abrasion resistance you'll increase the strength of the garboards far beyond what the missing .5mm would give.
Charlie