Aluminum repair, can I glass over it?

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SFC Hall
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Aluminum repair, can I glass over it?

Postby SFC Hall » Tue Jun 20, 2006 1:17 pm

I just picked up a free 14' Jon, made by Sears... this thing has the thinest aluminum I have ever seen on a boat. the seats, are broken away from the hull, the transum is rotted, the bottom is dented and it leaks....

I figure new transome, plywood seats glassed in, glass the bottom and it should be floatable... BUT will the epxy resin stick to the aluminum?

thanks

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Postby Graham Knight » Tue Jun 20, 2006 11:44 pm

Hardly anything sticks well to aluminium, most things that do, like paint, chemically etch themselves to the surface, epoxy will probably peel right off. If you really key the surface well you might just get away with it, but it may not last long.
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Postby Tim Hancock » Wed Jun 21, 2006 4:15 am

Glass and aluminum have different thermal expansion rates, so eventually if you glass the bottom, it will probably delaminate over time.

Aluminum can however be bonded with epoxy if the surface is properly prepared. In fact Grumman Tigers and Yankees (aluminum airplanes) primarily are bonded together with epoxy. The key as Graham kind of eluded to, is cleaning then etching/treating the surface of the aluminum so that bonding will occur.

Just giving it a wipe down with a rag soaked in laquer thinner is not goin to cut it.
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Postby slartibartfast » Mon Nov 27, 2006 10:29 pm

i know this one is an old stream but i have seen some stuff you can buy, not sure where but posably bass pro shops, to patch alluminum boats. it looks like a large green eraser, then you melt it with a propain tourch into the hole.
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Re: Aluminum repair, can I glass over it?

Postby michelle » Wed Dec 13, 2017 3:59 am

Glass sticks hardly over aluminum. I recommend you to take an expert's advice.

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Re: Aluminum repair, can I glass over it?

Postby lakeracer69 » Wed Dec 13, 2017 7:17 am

Why are you posting in a thread that is 11 years old?
As Conan the Barbarian says, " It's not how hard you can hit, it's how hard you can get hit and remain standing".

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Re: Aluminum repair, can I glass over it?

Postby Kevin Morin » Wed Dec 13, 2017 2:14 pm

Lakeracer69, bumping old threads can be useful is there's new info like products or methods that have come up in the mean time? Sometimes old threads have a problem waiting a solution and it comes up over the duration of the older threads' archival storage? Sometimes we may have a new reader who's thinking of a repair of an older boat and might see the bumped thread? Might be helpful for some readers?

In this case, the transom replacement alternatives have expanded a bit and so have the epoxy products, not that either of these changes will help the OP's boat 11 years on?

The original, super-low-cost, pressed, and roll-formed jon boats, mostly riveted of thinner not-marine grade aluminum may or may not be worth spending much effort to rebuild given how 'disposable' they were designed? After a period of use, many end up as raised bed planters here- but then these boats weren't planned to carry max load in a swell- they were more intended for fresh water lakes or streams so Alaskan's over taxing these thin hulls' design limits may have contributed to their early relegation to the garden?

The wood/plywood transom inserts were surely a short term solution to stiffness that are pretty much assured to rot out, either the wood OR/AND the metal sheathing. Replacing it with an aluminum framed and plated/planked hollow transom assembly wasn't well known back then and is now fairly well known- but may cost as much as another used jon boat in better shape? So, while there is a good solution to the decade old problem of transom failure by wood and metal rot- it may not be worth it to even try?

The epoxy products of many types now being sold for adhesion to aluminum have increased in performance and number (I'm not sure I've ever seen polyester resin adhere well or solve aluminum problems long term) so there may be another whole discussion available to explore in regard these products' as they've grown in number and capability to repair.

I do agree that different expansion and contraction rates and co-efficients of heat transfer will make any adhesion a challenge- but the newer materials can be used in surprisingly difficult applications and stick to the metal.

StarBrite (tm), Marine-Tex (tm), JB-weld's aluminum compounds, West Marine's G-Flex (tm) are just some of the products that are supposed to adhere well, remain bonded and stay on in both expansion and contraction of the underlying metal. I've not had extensive experience with any of these compounds- and I'm a welder so I like to relying melting the metal to itself instead of adding cold goops to seal - but I've also had more than one fisherman tell me of great success in patching, sealing and stuffing up cracks with these various products.

Welcome to the Glen-L Forum michelle, hope you're planning to review other Metal category posts and comment? Some of the threads could use more comment, I'm sure, and rereading the archives is a great way to learn more about the metal category of the Forum. Its always good to have more welders or metal workers commenting in this category.

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Re: Aluminum repair, can I glass over it?

Postby Kevin Morin » Sat Jan 06, 2018 4:23 pm

I occasionally get emails, since mine is published, or sometimes these types of conversations begin with PM's on the few sites I frequent; communications asking questions that I'd like to deal with online, at the various Forums, because there's a potential that my list of mistakes (metal boat building experiences) could contribute to the avoidance of my errors by others?

So, I'll attempt to mention my limited experience with this topic that is the subject of a couple recent communications directly to my 'inbox'.

The subject is; providing my opinion about redoing a production/riveted/press or roll formed boats' factory installed transom.

NOTE: most jon boats, many other forms of high volume, thin scantling, rivet seamed boats use a transom of plywood sandwiched between a 'wrapper' of aluminum sheeting.

This type of transom is filled with plywood because that is the lowest cost means for the manufacturers of this class of metal boats to deliver a transom that will carry the hp rated for that particular hull. (I assume? but don't know that to be the cause for this design?)

By covering the plywood with very thin sheet metal and thru-fastening, the impression is left with the buyer that these are actually metal boats! The truth is; they're composite boats with metal shells and if that were all the impact the design had on longevity (?) nobody would care.

However, since the manufacturers are mainly concerned with 'functionality at a price point' and not longevity- their transom designs' "time bomb" is ignored in favor of sales volume due to lowered price points.

The buyer is told of the transom 'time bomb' in terms that are 'legally' defensible-the eventual deterioration is not explicitly described- but the factors are well described: so there can't be a claim for misrepresentation. Further.... the fine print may well explain the need to 'dry the boat after use' .... completely eliminating any legal claim for the eventual deterioration of these sandwich ply- transom assemblies. Finally, the actual deterioration of the composite transom usually occurs long after the warrantee period expires- so, there is no assertion made at the sale, or expected to be in effect; when these time bombs go off.

I'm not engaging fault finding, I'm not engaged in any claim or any assignment of blame to a boat manufacturer who uses this wood/metal sandwich to solve the design problem of transom strength versus boat life. I'm providing an educational thread for the Glen-L Forum readers who may be involved in these boats' use. I will attempt to examine the 'in's-n-out's' of these transoms in a few posts as an answer to the several owners, prospective buyers, and even a few restorer's who have written to ask my opinion on this subject.

This is not a rant against boat manufacturers who use composite wood and metal transoms, this is not an attempt to assign blame to either the builders or the buyers and users of boats with this design element built into this class of boats.

I am writing to explore the problem for those who have a new boat (1), to explore maintenance for those who may have one of these transoms on their boat and may care to read about what could make them 'last longer' (2); and finally I intend to take a stab at replacements if the original build has deteriorated to the extent that the hull's integrity or water tightness is compromised. (3)

This will take a few posts, and won't happen in a day. I'd be happy to field/reply/explain my view of ALL questions, in any aspect of my remarks, and do not expect to be the 'last word' on this subject. (or of any other metal boat topic, for that matter!)

This post and any others might be best posted to another, new, thread (?) but since the metal category seems to be Glen-L's narrow niche thread I'll just leave these posts here bumping this glass-over repair thread that has gone dormant.

[Mod.s, please (feel free to) move this where you think it more appropriately located?]

Next, The Design of the Problem.

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Re: Aluminum repair, can I glass over it?

Postby JoeM » Sun Jan 07, 2018 8:15 am

New thread or resurrected thread, i'll let mods deal with that. I just want to thank you for all the informative posts on the subject of metal boats. I'm not building one, I don't have one, and my metal working ability is slim to none (just took a blacksmithing class though so I'm improving, slowly). But i'm still interested in this subject and love adding more "tools" to my brain. I will be looking forward to your posts expanding on this topic.
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Re: Aluminum repair, can I glass over it?

Postby Kevin Morin » Sun Jan 07, 2018 5:37 pm

JoeM, thanks for the kind words, I hope this short series helps you to expand your knowledge and helps others if they're involved with the type of boat which has a composite wood, plywood and sheet aluminum transom assembly?

The transom on an outboard powered boat has to be able to remain stiff with the entire boat's mass pushing and pulling against that one panel. This is not "jump-off-the-page" obvious unless you've spent some time looking at the loading or forces involved- so I'll begin this review with that step.

If you have a row boat, there is no more thrust on the transom than the sides, bow or any other hull panel. Inboard power boats' transoms don't have to be half as stiff, in proportion, as an outboards transom panel. In the row boat- thrust is provided along the sides' main panel so they form an incredibly 'stiff' structure to accept those forces- not to mention the power involved is not much of a fraction of one horse power. Inboard's accept the thrust of the engine's forces on the propeller on the two engine timbers- often tied to many transverse frames- and not on the hull's transom.

However, if the boat in question is pushed by an outboard engine mounted on the transom, then that transom design has to be much stronger - IN PRopORtoIN.... than in other boats' hull panels that merely resist in water forces to float. The power of an outboard engine is pushing on the transom at the bottom of the engine mount and PULLING at the top of the engine mount (!) just below the pivot hinge tube of the engine.

So, an outboard powered boat's transom has to #1 hold the wt of the engine for the life of the boat; #2 Translate the engine thrust to the rest of the hull so the engine's power is translated into movement through the water, in forward and reverse; #3 resist the pulling force of the outboard engine trying to pull the transom top off to the stern of the boat! and.... #4 most importantly - this hull panel has to be stiff enough to do all these jobs while the boat is in water- so.... the Bow acts as a lever against the transom since waves can lift (Pitch) , push side to side (Yaw) and if unequally submerged (?) this same long lever will act to twist (Roll) the entire hull as well!!!

The transom has to hold the engine, convey thrust to the entire mass of the hull and resist the various forces acting as a huge lever at the bow. (And) to make this panel even more critical, if the boat will plane (? and many do) THEN: all the forces involved become much stronger, more powerful and require even more demands of the transom panel.

OK, I said all that to point out that thin scantling, press and roll formed sheet aluminum boats can get by with thin bottoms, thin sides, thin bows, thin seats, thin gunwales and thin lockers... But they almost all need a thick and stiff transom.

Let's make sure to exclude welded plate boats here; and let's define plate versus sheet as terms in this discussion- so I'm not being confusing while attempting to offer clarification! I'll call "plate" (for this thread) any thickness of aluminum that can be welded economically AND performance wise resulting in a reliable boat- compared to riveting. AND I'll call sheet for this thread, aluminum that is more economically riveted over welding to produce a useful and reliable aluminum boat.

In general plate boats are rarely thinner than 1/8" or 0.125" thick and that is almost always confined to 5052, 5086 or 5083 alloys, while; roll formed hulls are rarely thicker than 0.060", 0.080" and once in a while 0.100" and often, if they are even 5052, they are non-heat treated, to increase the malleability so the roll and press forming will have more function with less stress cracking!

Its important to recall at this point: thin roll formed aluminum hulls are MUCH, MUCH less expensive than their much thicker, much heavier and harder alloy, all-welded boats! (Think; Volkswagens to Peterbilt Trucks!)

A plate (welded) boat's transom design meets all the needed structural properties but does so by the thicker scantlings available more than adding composite filler materials like the thin press formed production boats we're discussing. It is not uncommon to see 1/2" or even heavier solid aluminum plate incorporated into a welded aluminum boat's engine mount and transom assembly. Most of the production boats we're examining use a wood filled hollow box style transom to create a panel stiff enough to meet all the requirements for that class of boat.

It is completely reasonable engineering to build a transom that "does the job" for a light wt boat. A 16' jon boat hull- complete(!) does not typically weigh as much as one half the bottom hull plate and framing for a 22' offshore welded plate boat!

The solution in most lighter wt, formed hull panel, riveted seam production boats is to make the transom panel of a sandwich of plywood (some have used planks glued on edge) with a wrapper of sheet aluminum inside and outside of the plywood.

The plywood, when new and dry is strong enough to hold most small boat rated engines (<30hp) and if kept dry can remain at its original design strength for many years. If the composite panel of ply and riveted aluminum cover is kept dry, not allowed to collect moisture over time and the engine size is kept to the original design limits: THERE IS nothing wrong or problematic with this composite wood and aluminum transom.

The problem comes when the panel's wood core becomes wet, water logged and begins to not only corrode the aluminum sheet covering but begins to delaminate while it corrodes the aluminum covering.

If the composite transom panel were either built to a higher standard of sealing, or if owners could add some higher standard of maintenance to the original build- a dry state of the materials would allow longer life, safer service and greater use of these boats for their intended service.

We need to look at the design in detail now: Then we'll get to ;What about the design makes water a problem? and move to what could be done to a new boat in this class or what could be done to recover one- and then to what ideas could be effective in an entire transom replacement?

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Re: Aluminum repair, can I glass over it?

Postby Kevin Morin » Tue Jan 09, 2018 3:20 pm

We've taken a look at thin scantling production boats' transoms as critically important to the usefulness of this class of aluminum boat. In that review I've tried to find a way to discuss the importance of stiffness- rigidity- structural integrity as the primary driving priority that has lead to manufacturers' decision to use plywood covered in thin sheet aluminum for their "solution" to the requirements of these boats.

Here, I'd like to briefly remark about plywood's performance and failure mode- before we move ahead.

Plywood is one of the stiffest, strongest, most cost effective of all mankind's manufactured sheet goods materials. Plant fibers are just about the most elegantly designed of the Good Lord's nearly infinite number of elegant designs! If we roll a log in a huge lathe; peel the wood off in long sheets; then cut the miles of veneers of different woods into panel sizes; finally, glue a stack of these thin sheets of wood into many different arrangements of fiber direction, thicknesses, types and species of wood? --- We get plywood a manmade sheet product from trees' fibers handled in different ways to engineer and improved performance material.

That results in "super wood". Plywood is literally super wood- all the main properties are improved: rot resistance; structural properties (as compared to the weight of the final sheet materials); size of materials available; appearances are even enhanced if the outer veneers are taken from high quality logs.

Notice the entire key factor about plywood is that thin sheets of wood are glued in a stack of layers and then pressed, heated, and cured so a man made film between the layers is what holds the entire stack of thin layers of wood together.

It is also critical to understand that plywood fails to deliver on all its gains over solid wood when the glue layers break down or the stack's integrity is compromised and water infusion is the most common method of plywood failure. By either breaking the glue down OR, worse by making the fiber-to-glue bonding layers fail; the glue in plywood is the weak link in failure and the primary strength addition when that same glue is intact bonding to the fiber sheets' surfaces.

If we consider a house that is 40-60 years old, where the roof has never been compromised; that house's plywood flooring, or sheathing is still intact and the house's strength is still intact too. In fact: in the 1964 Alaskan Earthquake; plywood sheathed homes were slid 1/4 mile from their foundations! These homes were on a clay filled hillside which became liquid (or mud) when the quake shook the bluff on which these houses were built. But the homes were so rigid, so stiff from the plywood and stick frame building methods; many of these homes were virtually intact when the landslide they rode down to the Cook Inlet flats stopped. I'm just showing that dry plywood is one great man-made, engineered material that beats the original wood by several factors of 10 in overall performance.

Plywood also beats comparable WEIGHTS of both steel and aluminum- in many categories of structural performance.

Therefore; if you wanted to hold an outboard engine, absorb the thrust of that engine, resist the entire hull's moment arm(s) of force to lift, roll and twist a boat's hull: plywood is a great choice as a light wt, inexpensive material that delivers extremely good structural characteristics for its contribution to weight at a given cost.

That is all true until the plywood is allowed to get wet, stay wet, and to have water penetrate its various layers. Then, plywood is not a very good choice for the jobs required of it in thin scantling production boat transoms.

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Re: Aluminum repair, can I glass over it?

Postby Kevin Morin » Wed Jan 10, 2018 1:13 pm

In different threads, here in the Metal Category, I've tried to discuss corrosion of aluminum as the main failure mode of the Miracle Metal***. Water, by itself, is not corrosive of the marine' alloys, as the 5052, 5086 & 5083 along with 6061 series alloys ( most commonly used in welded boats) are not easily corroded just by water alone.

However, if water is acidic (or too base) it can contribute to aluminum corrosion and therein- lies the problem for the composite wood & aluminum transoms used on thin scantling, press formed riveted seam aluminum boats.

Another method of aluminum corrosion is galvanic- where different metals, when wetted along with aluminum, form a type of battery and the aluminum usually gives up molecules to that 'cell' resulting in corrosion.

Let's take a look at how the wood/aluminum transoms' design and construction could lead to corrosion of the aluminum WHILE the plywood inside is also deteriorating!

[NOTE: I don't know the alloys of press formed/roll formed jon boats or other manufactured boats! That is: I'm not sure of the alloy, I'm only familiar with the few 'welded boat' alloys I've listed in regard performance and corrosion resistance. Also, I'm reporting on personal experience with a sampling of boats brought to me for repair/patching/rebuilding/modification over a period of years and I don't have experience with all brands, all models, or any dialog with the manufacturers of this class of boat.]

In my experience these transom assemblies usually have 0.060" or thicker material that has been layed on the plywood and riveted along the edges (top, sides, bottom) to some specialized shape- like a channel or a channel with a flange (chair shape in profile) or some other, often thicker, piece of aluminum. However I've not seen any of these assemblies that were water tight AT air test pressures! The seams usually have some sealant, either a glue or an elastomeric strip in the rivet seam- to provide the original water tight seal required of a boat's hull. However, this outer edge or panel perimeter seal is often compromised at construction completion!!

Most of the transoms are 16" to 24" from bottom to top, and 4-5' wide- so the sheet aluminum covering needs to be fastened to the plywood to keep the covering from billowing out- or bulging away from the wood. Also to increase strength, fastening the metal covering and the filler/core/plywood panel will increase the overall transom strength.

However, one of the built in failure points of the composite transom design is these fasteners used to help hold the aluminum to the core plywood! Depending on the metal alloy of the bolts, rivets, screws used to hold the aluminum to the wood (?) a galvanic cell can form around those fasteners- corroding the aluminum if the joint is wetted without drying.

These fasteners, of many types offer a leak path for water to begin invading the interior of the composite transom. If the wood is glued to the aluminum as well as bolted or screw fastened (?) that would reduce the spread of water in the boundary layer between the two materials. However, not all builders use glue in this interface, and those who do; seem to add the glue in narrow strips instead of insuring a uniform layer.

This means the glue may not work as a leak limitation, sealant boundary to water intrusion around a screw or bolt hole in the metal. If the hole for any fastener is not in an area that has a glue layer under the hole in the materials' surface boundary - then water can spread all around that entry point by capillary action- and I have seen this happen.

Now the water is becoming a thin film, that gets de-aerated and becomes acidic, that promotes aluminum corrosion via 'crevice corrosion' or 'poultice corrosion' and that transom will likely 'rot' from the inside out.

Another form of this problem comes at the engine mount bolts- they are mostly through bolts of different diameters depending on horsepower. These openings are drilled by an engine installer - not always preformed by the boat's builder/manufacture. As a result the openings are not always prepared using a design, tooling and method of installing these bolts that will prevent water intrusion into the composite transom.

if you drill a hole in plywood and put a funnel on the surface and fill the funnel with water (!) will anyone be surprised that over time the water will absorb into the wood fibers, and begin to delaminate the ply's? What if the plywood is put in a 'metal box' and heated by the sun, then cooled at night with the water still present? Will any one be surprised that this piece of plywood begins to weaken and deteriorate?

What if the thin sheets of aluminum are left against wet plywood, especially if the plywood's glue will break down into acidic compounds when combined with wetted wood fibers? The naturally occurring corrosion of a composite transom's inner aluminum surfaces is the result of allowing water to intrude into the panel's core and remain there.

Even if the transom can be dried out- periodically- if the leak paths are not sealed so the original corrosion can be 'starved of water' in the future- the repeating action of wetting, will allow the already acidic site of corrosion to cycle - eventually the thin metal will be eaten through by this cycle.

I hope this report of experience attempting repairs or patching this design element in production boats makes sense. IF I've skipped too many steps, please take a minute to find the other corrosion posts, and give a read to help you understand the three types of aluminum corrosion so my remarks here are clarified- if they seem to assume too much of the readers' knowledge?

Having discussed the problem, or some aspects of the problem, I'd like to try and suggest some steps that may help these types of transoms to be stable and reliable for many years longer than they might if not maintained?

cheers,
Kevin Morin
Kenai, AK

*** The Miracle Metal is the term used for aluminum when it was first refined in the late 1800's or thereabouts.
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Re: Aluminum repair, can I glass over it?

Postby Kevin Morin » Wed Jan 10, 2018 2:51 pm

Whenever I start to post a series of articles or comments; inevitably (!)- I get busy with the days' business and time to compose a post becomes limited. The next few posts need to be illustrated and that will take a few more days (?) because other projects have come in to claim priority on time.

Hope that the Forum won't mind if I leave these remarks to 'soak' and come back when time is more affordable?

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Kevin Morin
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Re: Aluminum repair, can I glass over it?

Postby JoeM » Wed Jan 10, 2018 3:48 pm

Take your time Kevin, we all understand! Thanks for letting us know.
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