epoxy over aluminium hull

Discussion in 'Metal Boat Building' started by richard gray, Apr 16, 2014.

  1. richard gray
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    richard gray Junior Member

    would epoxy resin bond to an aluminium hull to use as fairing and final coating? epoxy paint on top?photo of the amphibious vehicle prototype drive train. hull cut out is for rear wheel, with a full skirt added later.
     

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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    I have seen some horrible poultice corrosion under epoxy on aluminium, maybe it is all in how you prepare it first.
     
  3. PAR
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    PAR Yacht Designer/Builder

    If the alloy is etched first, bonding issues can be all but eliminated. This is for paint. Epoxy takes the same approach (exposes fresh aluminum), but is typically done during application. Most formulators will suggest you scuff the raw aluminum while applying the epoxy coating. This can be as simple as using a wire brush to scratch the raw aluminum, under the epoxy wetted surface or most prefer to use a Scotch Brite pad or similar (wet dry paper). This not only exposes unoxidized aluminum, but also prevents fresh oxidation, because it's under the wet goo. What I've done with good success is to glass bead the area clean, followed by a quick wipe and tack rag and put down the epoxy immediately after. On a technical level, there is potential for some level of oxidation, with this technique, but it's a small percentage and the bond is still quite good.
     
  4. mastcolin
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    mastcolin Senior Member

    Ideally blast the alu with appropriate grit media...failing that disc it with p24 on angle grinder. If you use a big grinder you will do area in no time. Messing around with wet sanding resin is madness for big areas.

    DO NOT use a wire brush unless it is suitable for alu - if you use the wrong type you grind/break the steel bristles into alu and it will create battery under the coating. This is not theory, this is seen in practice.

    After you blast or disc, I strongly recommend NOT to use a wipe down cloth. The sharp edges will tear off fibres from the cloth and you will them paint them into surface. Not so great problem between layers. Bloody nightmare on alu as this has enough corrosion issues in marine without fibres on the surface, possibly linking to exposed surface. Degrease the smooth surface BEFORE disking. Keep greasy hands off after!

    Don't waste your time coating with resin before making filler. Buy a proper primer. This way you will also get extended overcoat time, you will have way less issues with temp/humidty...and the paint will adhere better than a resin will on al. They will probably be cheaper than your resin per litre.

    Trust me. No one goes messing around when prime painting alu navy ships, 100m alu superyacht or 300m cruise ship superstructure. They use paint. Take pick from various suppliers. Look for extended overcoat type ie you can leave it exposed for (limited but in terms of months) before you have to fill.

    Aluminium skin and steel frame? Get busy with trying to keep everything bonded together...and insulated without getting corrosion?:) And remember to give it good freshwater rinse everytime you go in salt water. I can see problems for you otherwise.
     
  5. yofish

    yofish Previous Member

    Pardon me, but I have no clue as to what the attached pics have to do with your query. What I see seems rather not boat-like.
     
  6. richard gray
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    richard gray Junior Member

    paint on aluminium

    it is an aluminium hulled amphibian prototype . i will need to fair and paint
     
  7. yofish

    yofish Previous Member

    Why fair? Cosmetics? Obviously (?) this is not some high speed world record attempt? just Paint it. I build aluminum boats. The best coating I've ever encountered is 100% blast, zinc chromate, Devoe 235, followed by the anti-fouling - (bring back TBT!).

    THE foundation, in IMO, is the blast and the weather when you paint. All those little sand blast pockets hold paint mechanically and secretly support the magic epoxy theory, which, in my experience, fails all too often. Unless she has help.
     
  8. richard gray
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    richard gray Junior Member

    paint on aluminium

    i have some axzo nobel? alumi grip primer and hi gloss ,should be oK
     
  9. mastcolin
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    mastcolin Senior Member

    What primer do you have? I am only asking as you mentioned filler. Some alumigrip primers are for aluminium but in different situations. ie no or minimal filler. Also the surface prep is different eg chemical etch or light sand.

    If you disk or even rough blast your toy you will get rough profile (50-70microns). This will mean you get a thick etch primer layer in the valleys...which may split under the filler due to the stress the filler puts on it.

    Just something to be aware of.
     

  10. richard gray
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    richard gray Junior Member

    i have a high build PPG aerospace CA7755A green urethane compatable. for aluminium, with urethane over
     
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