How to refinish aluminum window frames

Discussion in 'Metal Boat Building' started by pescaloco, Sep 12, 2009.

  1. pescaloco
    Joined: Feb 2006
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    pescaloco Senior Member

    Hi,

    I have a boat that has LP painted aluminum window frames that are blistered under the paint surface.

    It is not practical to remove for sand blasting.

    Can a good "spot" repair in both cosmetics and future corrosion prevention be made ?

    I would like to sand down / wire brush pitted areas, etch, prime and top coat with Awlcraft 2000 or similar.

    I am also willing to prep and paint the entire frame if that is a better way to go.

    Any advise on materials and prep procedures would be much appreciated.
    total materials for top coat are aprox 1/2 quart

    Thanks
     
  2. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    If you mask very well all surrounding areas, you should be able to sand-blast "in place". Check with people who provide portable sand-blasting equipment in your area. Make sure mask is thick near the aluminum and well stuck down.
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The most likely reason your LP paint failed, on the aluminum frame is corrosion of the aluminum. This suggests surface prep was to blame (usually is). You can attempt a repair, but generally if you have some corrosion rearing it's head, you have more that just hasn't shown up yet.

    The typical procedure, you've out lined. I've had good luck skipping the etch and using straight epoxy. I'd sand the frame, quickly wipe with a tack rag then apply epoxy immediately, literally with the tack rag in one hand and the epoxy brush in the other. The resulting surface then can be treated as any coated with epoxy and prepped for paint.
     
  4. pescaloco
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    pescaloco Senior Member

    Thanks guys

    The boat is going to be in the water at a "Yacht Club" tough to do any heavy duty stuff.

    I have allways sent my aluminum parts out and had the sadblast/coating company do them.

    Thanks Par, glad to hear I can sand/solvent wipe and go straight to epoxy.
    Should I use Awlgrip 545 or is there a Zinc/epoxy primer you recommend ??
     
  5. PAR
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    PAR Yacht Designer/Builder

    If you've worked clean you can skip the primer, but if you need to build the surface and smooth things out, then you may consider a building prime.
     
  6. Jimbo1490
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    Jimbo1490 Senior Member

    Apply 2" wide metal tape to the fiberglass substrate immediately adjacent the frames and also on the glass immediately adjacent the frames. Use a couple of layers of the foil tape, if it's the thin type from the home centers. Then get one of these things and spin it on a buffer, NOT a grinder, at about 1500 rpm and buff the corroded areas using only light pressure, never pushing or spinning the wheel too fast. No need to strip the paint off first; the brush will do that too. Keep it moving as you buff, allowing the bristles to approach the corrosion pits from different angles. Sometimes it helps to apply a layer of masking tape to the outside of the brush to make it stiffer until it has 'broken in' and all the filaments are a little shorter and of uniform length. With this unique tool, you can remove ALL the corrosion back to bright clean aluminum without making too much mess.


    Afterward, you can apply a surface treatment such as a chromate conversion coating such Alodine 1201 or Alodine 1132 phosphate conversion. There is also a new treatment product on the market which is not a conversion coating, but nevertheless produces outstanding adhesion on all metals, which is called Prekote. Alodine 1201 is a liquid soup of highly toxic heavy metals and should not be spilled into coastal waters, and many marinas frown on it (rightly so) and anyway we now have a viable alternative in Prekote which is non-toxic.

    Alodine 1132 is also toxic, but is dispensed though a giant 'pen' which looks like an enormous felt-tipped marker so not at all likely to get spilled and also does not require rinsing (so no toxic waste water to catch) the way Alodine 1201 does. That thing is one expensive pen, though!

    Both Alodine 1201 and Prekote require specific procedures in application and you should familiarize yourself with them and follow them as subsequent paint adhesion depends on adherence to these. Pantheon chemical has several videos posted demonstrating the correct procedures for the use of Prekote in several different applications. Alodine 1132 is the most forgiving of these surface treatments to apply as you just brush it on with the giant pen, let it dry then paint.

    Note that you MUST NOT solvent wipe a bare metal surface that has been treated with Prekote! Let dry, tack wipe and paint. Nothing more!

    Aircraft Spruce will sell you a single quart of Prekote which should be plenty enough to do a few window frames. I recommend that you procure a foaming pump sprayer to apply the Prekote product.

    After surface treatment, you should prime with a primer containing hexavalent chromium. The common 'Mil Spec' (Mil-PRF-23377) primer is such a coating as it contains strontium chromate. This can be brushed on. Wait at least 12 hours to recoat the Mil Spec primer. If you wait longer than 5 days you will need to scuff sand to get adhesion of the topcoat. But if you recoat before 5 days, you don't have to do anything but paint. If you cut through the primer when you scuff, you really should re-treat those bare metal spots and re-prime. Obviously it's best just to topcoat within the re-coat window of the primer.

    An experienced refinish guy can get all this done in a day, maybe 2 if there's a lot of frames to re-work.

    Jimbo
     
  7. pescaloco
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    pescaloco Senior Member

    Jimbo: Thanks that is a very complete run down I don't know how you did that with the links embeded or if I have just been sleeping, never seen it done like that in a post before............ Thanks !! I saved to my favorites

    Par: Thanks, as allways your information is and helpfull.


    Mark
     
  8. Landlubber
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    Landlubber Senior Member

    Nice work Jimbo, thanks for that info.
     
  9. Donovan
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    Donovan New Member

    Thanks for the information Jimbo. This really helped me out a lot. Hope that you will clear everyone’s queries. If I have any query I will get back to you.
     
  10. Landlubber
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    Landlubber Senior Member

    Just as a matter of interest, you can get 4 inch variable speed angle grinders, I have one and it is a very useful tool, fittings such as the nylon brush for instance can then be placed onto it. I use it with 3M doodle bugs a lot for this sort of work.
     
  11. pescaloco
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    pescaloco Senior Member

    I surprised to see this older thread pop up.

    Glad you posted, so do tell who is making a good variable speed angle grinder
    I have never seen one, but being a tool freak I think I need one

    Are you using a manufactured disc scottbrite or actually adapating doodle bug and or hand pads to the grinder ?
     
  12. alan white
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    alan white Senior Member

    The Makita is tough. Bosch is good too. One thing to check is the trigger mechanism. Some are ridiculously hard to operate, some much better.
    There are a lot of attachments for angle grinders--- 3M makes a setup for abrasive pads to spin onto. Nothing has to be customized.
     
  13. pescaloco
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    pescaloco Senior Member

    I think I am getting old, I remember this came up before about variable speed 4 in angle grinders, and I forgot.

    My two Makita 4.5 angle grinders are 10 years old (used and abused) Awsome tool.

    When Landlubber said Doodle bug pads I think of the woven plastic hand or brush head mounted pads, thats what peaked my interest.
     
  14. Landlubber
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    Landlubber Senior Member

    see 3M Roloc pads, they really are fantastic.

    I also use them with a Dynabrade mini sander, does incredible detail work for you.
     

  15. pescaloco
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    pescaloco Senior Member

    I use role locks for metal refinishing 2 or 3 in discs mounted to an arbor/plate for use in a die grinder. Do they make then with a mounting system for use on a 4 1/2 angle grinder ?
     
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