Adhesives for aluminum

Discussion in 'Metal Boat Building' started by Poacher, Mar 4, 2017.

  1. Poacher
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    Poacher New Member

    Can anyone tell me what is the best adhesive for gluing aluminum to plywood
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Will the join be underwater ?
     
  3. Poacher
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    Poacher New Member

    No it will be isnideman should never get wet
     
  4. Barry
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    Barry Senior Member

    3M Marine Polyurethane Adhesive
    5200 permanent,
    4200 is easier to remove

    If possible, scotchbrite the mating surfaces, and give it a quick degrease on the aluminum side
     
  5. PAR
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    I disagree in the use of an adhesive sealant, like the polyurethanes from 3M or similar. These don't have the elastic modulus necessary, except in lightly load elements. Epoxy would be the appropriate recommendation. A seal coat on the plywood and a good 100 grit scratch on the aluminum just before neat epoxy application, to remove surface oxides. Next a thickened mixture applied and the parts are brought together for the bonding. Not much pressure, just enough to insure ooze out around them and full contact.
     
  6. Barry
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    Barry Senior Member

    http://multimedia.3m.com/mws/media/327283O/sealant-5200-tan-td-sheet.pdf

    Attached is the spec sheet for 5200 with reference to a flexible bond. We used this on all of our aluminum boats when there was not other choice to affix wood or aluminum to the aluminum hull. The tough part about this product is if you make an error and have to remove the piece, we had to mechanically remove the part.
     
  7. PAR
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    PAR Yacht Designer/Builder

    I'm familiar with 3M 5200's physical properties and I'd agree in some applications a flexible bond is desirable, but I'd still not use 5200. Removal is one concern, though a hot (read torch and putty knife) blade will greatly help it's separation, the surface will need considerable prep afterward. My issue is if you want to "marry" the parts, epoxy is the better choice. On the other hand if it's a decorative element is, some flex may be desired, so I'd use a lower tack product, such as BoatLife. Removal will be easier and flexibility is greater.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Not sure why this can't be fixed mechanically if it is out of the weather and sealing is not critical.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Mechanical attachment is an option, though I'd want a mastic or sealant between the wood and aluminum, to prevent moisture from getting between them. A notched trowel and some goo in a tube, lots of screws or clamps until cure . . .
     
  10. dinoa
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    dinoa Senior Member

  11. Dukke57
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    Dukke57 New Member

    Hi I have a question concerning an aluminum below deck fuel tank . I cut the top off my 55 gal and am putting a 30 gal inside . I have 3/4 of an inch cavities around and under tank . I'm planning on foaming these cavities and not sure if I should coat tank before foaming , the 2 part epoxy is too expensive and someone had told me to use 1 part epoxy Which is garage floor paint , looking for some advice .
     
  12. Barry
    Joined: Mar 2002
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    Barry Senior Member

    I am assuming that this is a GAS tank, not diesel?

    ABYC has specific requirements for mounting aluminum tanks into boats
    These are some of the important points.

    1) The tank cannot just sit on a flat surface because if you get water between the bottom of the tank and what it rests on, in the absence of oxygen, you will get corrosion
    You must either set the tank on strips of plastic or on solid plastic. This plastic must be permanently adhered to the tank with a marine adhesive to keep water off the aluminum

    2) Any straps going around the tank require the same treatment, ie glued strips to the tank before the straps go around

    3) All fittings for the tank have to be either aluminum or stainless, never brass/copper

    4) Any metal components of the fuel tank must be grounded to the ground of the boat and the resistance to ground must be less than 1 ohm, so the filler neck, the tank and the level control if it is metallic must be grounded.

    5) If you are connecting rubber fuel line to the the fittings you require 2 stainless gear hose clamps per joint, same with filler hose. You have to ensure that the worm is stainless as well. Most automotive clamps have a galvanized worm and will rust
    There are also some other stainless clamps that will fill the requirement especially for the larger filler hose

    6) The tank cannot be supported by foam

    7) and ensure that you use Marine grade hoses for the filler and the fuel line,

    While ABYC allows foam around tanks, there are quite specific requirements to achieve a compliant installation. Obviously due to the chance of creating a corrosive environment for the tank. Better to leave this off the table, and leave room all around the tank, ensure that your existing tank has some way of shedding water into the bilge so your new tank will not come in contact with any water.

    You could private message Ike who was involved with writing the ABYC specs. Once you get him started on foam, you will probably not consider it.

    Re the plastic strips to mount the tank. I have seen UHMW plastic (ultra high molecular weight) used in this application. Normally it is white and slick and people sometimes call it Teflon.
    There are better choices only because it is difficult to get a good bond with adhesives to this material. For the sealant to attach plastic strips to a tank, something like a marine sealant adhesive 3m 5200 would be fine. Not RTV silicone sealant
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Properly painting the fuel tank should do away with most of the poultice corrosion issues.
     
  14. emendel
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    emendel Junior Member

    ive used an epoxy called pc-11. its a 2 part epoxy which is a thick paste. this stuff is amazing and sticks like you know what to a blanket. super strong, glues almost any thing. ive used it to fix a 6 inch crack in a septic tank of 100 gal. (1000lbs) still using the same tank in my camper for 7 years now. also used it to fix a radiator crack on my dads honda, he returned the new radiator after 6 monthes. that was also 5 years ago. i swear by the stuff. i put it over the cracked septic about 4mm thick and 2 inches on each side like a patch thinking that i would just use it to get the camper home and have never touched it again. only down side is cost... run me about 38 bucks to get 2 cans 455 grams worth. but i do live in the middle of nowhere in canada. prolly be like 15 bucks in the states
     

  15. espresso
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    espresso Junior Member

    Thermal expansion is the reason for flexibility

    If you want a durable joint between wood and aluminium, you have to allow the joint to expand and contract with temperature variations.
    No matter how strong the joint, if it is continually being put under stress every time the aluminium gets hot or cold, then the joint will fail.
    If it's not in the sun you may get away with it, but 3M 5200 is the way to go.
     
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