fiberglass over alum skin

[jspano]

i know this is considered like bringing a yahama to a harley rally.
but why can't fiberglass be used to repair alum boats.
i put some on a pc of alum as a test and it seems to be good.
just asking please do not kick me off the forum for asking


joe

 

[Steve Mahler]

Re: fiberglass over alum skin

i am no expert, but i would be afraid the two would separate with the flexing of the aluminum, over time.

 

[86 century]

Re: fiberglass over alum skin

For a repair or as a sealer

 

[Robert4Winns]

Re: fiberglass over alum skin

I am no expert, but I would guess that the two materials woudl have different rates of expansion due to temperature changes, which would eventually cause the bond to fail.

 

[jspano]

Re: fiberglass over alum skin

86

either or ....repair or sealer

 

[Bob_VT]

Re: fiberglass over alum skin

There are epoxies designed for aluminum and boat hulls. Fiberglass is not one of them.

 

[evildocrsx]

Re: fiberglass over alum skin

Hmmm.... What if... I cover the hull of my Starcraft with fiberglass and then pop out the aluminum hull leaving a mold behind. I could then replicate my Starcraft many times over, but with fiberglass. Would that work?

 

[Chinewalker]

Re: fiberglass over alum skin

Fiberglass on flat aluminum might work, BUT fiberglass doesn't easily conform to the bends, rivets, sharp corners, etc. of the aluminum, thus leaving air gaps, which will work into larger gaps over time. Plus, that will add a fair bit of weight, too!

 

[Bondo]

Re: fiberglass over alum skin

i put some on a pc of alum as a test and it seems to be good.

Ayuh,... So explain your Test sequence....

You can do it anyway you'd like,...
But,...
Polyester resin will fall off aluminum over time... Especially when subjected to the rigors of a boat hull...

 

[Bob_VT]

Re: fiberglass over alum skin

Please ..... you have 7 active threads ....... you already stated that you were going to use gluvit and 5200 for your hull....

no need to make a new thread with every troll oh question!

 

[jspano]

Re: fiberglass over alum skin

sorry for the TROLL question.

i was looking for answers away from my restore thread.

i wanted opinions from people who might not follow an alum restore.

i have kept all my post reguarding my restore to that thread.

have i done something to **** you off personally or are you just nasty to all!

joe spano (maybe i should start another thread on that subject)

i guess the answer i was looking for would have been to use marine-tex and cloth as needed

"Marine-Tex paste provides waterproof repairs that can be used with fiberglass tape or cloth to bridge holes and reinforce structural repairs as needed"

 

[PaulyV]

Re: fiberglass over alum skin

Interesting...so cloth fiberglass or CSM..? Does it specify?

 

[jspano]

Re: fiberglass over alum skin

it doesn't say but the gentleman @ the marine said as lond as you coat it it can be added. i told him of the small holes i had in my hull and was going to use this product and then put a alum patch over it and he said to check it out that the alum patch might not be needed. i think i ran across this stuff on the boat where it was applied and had mushroomed into the transom from the PO and i had a hard time preping this area. 80 grit sand paper didn't phase it.... heck a grinder was tuff but finally leveled it out.

"Marine-Tex Epoxy Putty FAQ-

Is Marine-Tex Epoxy Putty safe for potable water repairs?
Marine-Tex is not rated for potable water repairs.

Can I drill and tap Marine-Tex Epoxy Putty?
Yes, after it has fully cured Marine-Tex is drillable and tapable.

Is Marine-Tex Epoxy Putty resistant to gasoline and diesel?
Yes, Marine-Tex Epoxy Putty is resistant to gasoline and diesel.

Can Marine-Tex be used to repair gelcoat?
Yes, please see "how to..." section for details.

How high of a temperature can Marine-Tex withstand?
Depends on pressure and conditions. Up to 250?F constant temperature in a dry environment, with spikes up to 300-325?F.

What does Marine-Tex adhere to?
Metal, fiberglass, glass, masonry, ceramic, wood, most plastics.

What does Marine-Tex NOT adhere to?
Plastics like polyethylene and polypropylene, and also any unclean, oily, greasy, or otherwise contaminated surface.

Can I pigment Marine-Tex?
Only the White Marine-Tex can be pigmented. No pure color will be achieved by adding pigments. (We recommend epoxy-friendly pigments, like Fibre-Glass Evercoat's.) Do not use more than 5% pigment per total volume of epoxy.

Which color of the Marine-Tex is better to use for machinery bonds?
Gray. The Gray Marine-Tex is stiffer in contrast to the White Marine-Tex which is better for fiberglass repairs.

Are there metal fillers in Gray Marine-Tex?
No, Gray Marine-Tex contains no metal fillers.

What is the shelf life?
Two years in a closed container at moderate temperatures.

What is the pot life of Marine-Tex?
Depends on temperature, half an hour at 72?F.

Can you use thinner with Marine-Tex?
No, it will change the physical properties of the Marine-Tex.

Can I apply Marine-Tex under the water?
Yes, but the Marine-Tex is likely to wash away in moving water while it is trying to cure. The FlexSet is better for underwater applications because it is of a denser consistency. If you would like to try an underwater application, mix the epoxy above the water, then deposit it on wax paper or plastic wrap. Slide the wax paper or plastic wrap onto the palm of your hand with epoxy facing up. Take it below the water line and apply to surface. Be careful not to smack or pancake the product onto the surface, this will trap water under the epoxy. Instead, roll the epoxy onto the repair to push water out of the way. Leave wax paper/plastic wrap on the repair while full cure takes place for best results.

Can I apply Marine-Tex in dry conditions on a below-the-water-line application?
Yes, the Marine-Tex is an excellent choice for repairing gouges or holes that are located below the water-line. Once cured, Marine-Tex is impervious to water and many chemicals. Since putties will go only where they are placed, be sure that the Marine Tex has completely encapsulated the problem area. It is a good idea to sand the perimeter of the repair so that the Marine-Tex achieves a grip on the solid surface around the repair.

Will this epoxy cure in cold weather?
Epoxies need heat in order to cure. If your application temperature is not at least 60?F you must apply heat to the area before, during, and after the application in order for it to cure. We recommend you place a shop lamp approximately 12" - 18" in front of the application. The lamp will provide heat at a constant rate, so that the material's temperature is always constant. Do not apply a heat gun or hair dryer to the area, these types of heat will heat the area too much.

 

[PaulyV]

Re: fiberglass over alum skin

Thanks jspano...I just finished reading that on their website..I was premature asking you...then I went and read it...backwards eh??

 

[Bob_VT]

Re: fiberglass over alum skin

Flex set is a better choice and once you use it you will find is has properties of 3m5200 fast cure. The primary reason between epoxy and fiberglass resin (poly) is the reaction to the aluminum and aluminum based corrosion. The poly will eventually lose grip and is too brittle...... marine tex itself is brittle but being epoxy is stronger...... the flex set is epoxy but endures flexing.

Saltwater + aluminum do not get along..... and either does freshwater but the salt promotes the galvanic corrosion faster.

Yes you can use fiberglass cloth to "bridge" a gap but it will not add to the strength.

 

[PaulyV]

Re: fiberglass over alum skin

Thank You Bob..that answered all my questions..brief, and to the point

 

[erikgreen]

Re: fiberglass over alum skin

I agree with Bob, here's a bit more info.

Aluminum is a great metal for boats when bare because of its chemistry. Aluminum naturally forms a layer of oxide on its surface when exposed to oxygen... it's a naturally reactive metal.

Aluminum oxide is translucent, very hard, and has a higher melting point than aluminum. It's also close to inert, which means it protects the aluminum against corrosion very well. Aluminum oxide is what most sandpaper is made from, and a form of it is corundum, which is what sapphires and rubies are made out of.

The down side to the inertness and corrosion protection is that it's very hard to get a primary bond to it. If you've read a lot of posts here about epoxy vs. poly, you'll know that epoxy is a better glue (note I didn't say "better resin" or "better choice for boat work"... it's a better glue for sticking things to other things) because it can form a primary or chemical bond with most materials. A primary bond is much stronger than a secondary bond, which is mechanical. The two are comparable to welding metal vs. riveting. Welding makes the metal one strong piece, riveting threads metal through the pieces to be joined so they can't come apart.

That said, not many people weld aluminum because of the oxide and the heat properties of the metal. The oxide forms quickly and the metal underneath it will melt before it does... if you're not careful the aluminum melts into a puddle with an oxide skin on it. You can grind off the oxide, but it starts to re-form unless you're working in an argon or similar atmosphere box. Plus, aluminum doesn't change color as it heats like steel. Aluminum can be a few degrees from liquid and it'll still look like it's cool. Many people melt much aluminum into blobs on the floor while learning to weld it.

With me so far? Ok, the aluminum oxide layer on the metal forces most epoxies (those without chemicals to etch or remove it) to form a mechanical bond only. Even a primer like zinc chromate won't help because it forms a layer between the epoxy and aluminum that is weaker than the epoxy->aluminum joint would otherwise be.

Secondary bonds are hard to make strong and permanent. Check out Oops! thread on his hull extension to find out what he had to do to ensure that the poly resin he used would bond to his old hull (grind, grind, grind, acetone clean, vacuum...).

A patch attached to an aluminum hull with epoxy only would therefore have one strike against it. But it's worse than that because as has been mentioned the flexibility of aluminum and fiberglass are different. This means that the hull would constantly be trying to flex out from under the patch, working to loosen the mechanical (secondary) bond. When it fails it'll fail all at once, leaving you with an unpatched hole and missing patch.

The end effect is that the patch might last a while depending on use, but it eventually *would* come off. If the patch was aluminum it might do a bit better, but again it's still only weakly attached with epoxy.

If you rivet a patch on and seal with epoxy, that's permanent enough to be useful. Welding is even better for the most part since it makes a primary bond/one piece. But heating the metal to weld can weaken it, too.

So in a nutshell the best way to patch an aluminum hull is having a pro welder do it. The best amateur way is a riveted and sealed patch. The price you pay for having a light, strong, corrosion resistant hull.

Erik

PS: You can mold a fiberglass hull from an aluminum boat, but you'd have to smooth the boat first to ensure you could remove it from the mold... all the rivet heads and scratches would form mechanical bonds on a large scale with the mold resin. You'd never get the mold detached in one piece without a lot of work, and your eventual hull would look pretty strange...