joining alu and ply with epoxy

mbha · Post by **mbha** » Sat Oct 18, 2003 4:43 pm

I'm fully aware of the oxidation problem with aluminium and the resolving. Besides that, what's your opinion on building the hull in aluminium joining it to plywood framing using the epoxy filleting tecnique?

I'm building a hull in alu right now but I want to use ply for the entire internal structure such as floor, seats and so. Some will be a part of the structure. The framing in alu, even though I'm using 4mm (rest 3mm) there is pretty flimsy so I actually only want to have a boat with the shell in aluminium but built with wood stringers and bulkheds on the inside.

Sensei · Post by **Sensei** » Sat Oct 18, 2003 7:23 pm

mbha wrote:what's your opinion on building the hull in aluminium joining it to plywood framing using the epoxy filleting tecnique?

I would not do it... Aluminium is notoriously fussy as far as getting things to stick to it goes (and a few other things too)... When I was in the navy we had problems getting paint to stick properly to aluminium superstructures... If you used the wrong paint system/schedule it would come of in no time...

Also, don't forget, the boat will "work"... In a full epoxy/ply composite boat the adhesion of the epoxy is very strong and it is further reinforced by the glass (which adheres very strongly to the ply through the epoxy) which absorbs this "working"... I doubt the aluminium/glass/epoxy/ply bond will be anywhere near as strong as the glass/epoxy/ply bond...

mbha · Post by **mbha** » Sun Oct 19, 2003 7:13 am

I feel too that the bonding to ply should be superior. But then again, there are sportscars with aluminium structures bonded by nothing more then epoxy. Not to mention some boeing airplanes where the alu wings actually are glued with epoxy. I did a little "web" research outside the boat industry to see what applications epoxy where used in when it comes to aluminium bonding. There are some true amazing applications with extreme caution and it seems to work just fine.

I do remember that Jaques wrote somewhere that one could sand the surface with a grit paper wetted with epoxy. I think it was on steel though but the idea makes sense on aluminium too I would guess.

Bhatla · Post by **Bhatla** » Sun Oct 19, 2003 4:18 pm

I would be concerened with the different thermal expansion rate of wood and aluminium. Especiallly on a hot summer day for above waterline parts.

Years back, I was involved in building a fixture ( wood /aluminium) for environmental testing( temperature) of a military elctronics item.

We think one of the causes of failure was the different expansions rates of the two. Never really got around to study this in detail, but I think you should keep this in mind.

Bhatla

MikeS · Post by **MikeS** » Sun Oct 19, 2003 6:35 pm

It's your boat! If you try it though, I highly recommend you do the first launch alone (don't take your wife and kids) and use a real good life vest! Aluminum needs to be welded; there are thousands of aluminum yachts floating around this planet and not one have I ever heard of being glued together with epoxy or any other adhesive.

Boomer · Post by **Boomer** » Mon Oct 20, 2003 10:16 am

Well, I had an aluminum baot that I flat wore out --- no complaint, it was a good boat built like a tank-- but it started leaking around the rivets and developed stress cracks.

I polished, acid washed, lye washed, and did everything else I could think of to it and I never found any epoxy product that would stick to it long term. I think the aforementioned thermal expansion is the problem, especially with the thermal issues of summer temps for a baot left outside, uncovered.

I even flooded the inside with Gluv-it to try and stop rivets from leakng, and that didn't work for long.

Post by **jacquesmm** » Mon Oct 20, 2003 1:57 pm

It is not impossible to do but I would not take a chance.
To mix materials often means troubles. If you want to build an Al boat, use Al frames and weld or rivet but not epoxy and glass.

I have specified Al as backing plates, for example to install removable center consoles.
In that case, one option is to encapsulate a thick Al plate in the sole lamination the tap for machine screws or to glue it:
http://bateau2.com/modules.php?name=Sec ... e&artid=43
but that is not an endorsement of an hybrid material.
In the case of backing plates, I grind the thin layer of Al oxyde down before gluing. Acid treatement is good too.

Bhatla · Post by **Bhatla** » Mon Oct 20, 2003 3:20 pm

A while back I read somewhere ( I thought it was on the Loctite site, but just cannot find it now) where it was recommended to use methacrylate technology adhesives for structural bonding of aluminium, especially assemblies subjected to high torque and stress.

Anyone have any experience with this stuff??

Can Jacques comment on this ??

Bhatla

mbha · Post by **mbha** » Tue Oct 21, 2003 6:11 am

Thanks for all replies. I was in contact with a epoxy manufaturers laboratory and they basically say. With the right process in a laboratory environment it can be done. But chances are way to big that it will fail and it should be considered a very complicated method that requires both resources and knowledge unavailable to the normal person.

Basically, don't do it!

I wouldn't use rivets either. One reason for building a alu boat would be for it to last a very long time. Using rivets will require so many of them and such an attendance when mounting them that it isn't an option.

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