Alodyne & blisters; Questions on Re-painting an older mast.

Discussion in 'Metal Boat Building' started by RyanN, Oct 20, 2008.

  1. RyanN
    Joined: Aug 2005
    Posts: 19
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: North Carolina

    RyanN Junior Member

    First some background. I'm slowly working through re-building a 55' two piece deck stepped mast in my back yard. I'm close to painting it, but I'm unsure of the best procedures.

    The mast was originally painted with Awlgrip in the mid-80s. It was re-painted in the early 90s, probably when some corrosion issues were addressed.
    The paint is starting to fail with thousands of minute cracks. The underlying paint and primer looks good. In addition, there are some blisters where mounted hardware wasn't bedded properly. A few of these blisters are substantial. The mast also has a new masthead sheave box welded to it. Most of the hardware has been removed although there are a few pieces which can not be (through bolted and the nuts are no longer accessible).

    My plan is to sand the blistered areas with 60 until I get a shiny 1" border and well-feathered primer around the corroded area. Pits, some of which are deep will be glass bead blasted. I've done some of this already.

    The Awlgrip application guide lists two systems for what I'm doing. One for painting new aluminum and one for fixing blisters. The two systems use completely different products. My total aluminum area to be painted is probably only 5 SqFt.

    I would like to use the alumiprep 33/alodyne method on the new metal and the blisters as well. I know about the toxicity and will be capturing the runoff, using gloves, and full face respirator. I'm hoping that if I'm careful the amount of alodyne used will be minimal.

    So here's the process I want to use:

    • Sand and bead blast blisters.
    • Sand off existing paint to a layer which passes adhesion test.
    • Wait a week. I would rather do it all at once, but realistically I only have weekends available. Could this be a deal breaker? Shouldn't the alumiprep take care of any new or remaining corrosion?
    • Wash mast with diluted laundry detergent and water.
    • Treat unpainted parts of mast with alumiprep and alodyne as per Awlgrips application guide. Capture wastewater.
    • Dry mast with compressed air then apply a sprayed coat of mil-spec primer on areas wherealodyne was used. I've done some Alwgrip rolling and tipping but I don't spray so I have someone coming in to do this.
    • (wait to dry, probably cover mast and come back next weekend)
    • Fair badly blistered areas with awlfair (can I use west system & microbaloons?).
    • Spray mast with 545.
    • Sand everything fair (if needed).
    • Spray 3 topcoats.

    As an alternative, I've considered doing the blisters one at a time and using a small preval sprayer.

    Some other questions:
    • What's the best way to fill holes which are no longer used?
    • Is Tefgel the still the best bedding compound? Any issues with fasteners backing out?
    • Any suggestions on dealing with the waste? One thought is once captured to neutralize with baking soda and sodium thiosulfate (used in pools).

    Thank you for sharing your experiences.

  2. mastcolin
    Joined: Jun 2005
    Posts: 151
    Likes: 14, Points: 18, Legacy Rep: 150
    Location: The Netherlands

    mastcolin Senior Member


    Good luck. Masts are a nightmare. Sorry. I'll be honest. I work for large paint company in Netherlands, I know from experience.

    The good news is that it is only a nightmare in that it is a time issue. Technically it is no problem.

    I'll address your questions in no particular order:-

    1) after you clean the blisters/cracks, check your mast. The corrosion may be structural. I'm no surveyor but I know of masts failing after hundreds of hours of repairs on the paint. It's got to be said.
    2) The micro-cracking on the topcoat is just result of old age. Imagine if you sat out in sun for 20years! It will most likely only be in the topcoat. The primer is normally ok underneath.
    3) Blasting on the pitting is great idea.
    4) take care with grinding - the alloy isn't thick on a mast.
    5) the alumiprep is good idea - just make sure you rinse it all off well. Try to limit coverage on painted areas
    6) Use Mil-Spec. It is best you can get for alloy
    7) You can use selfmix filler if you want. Apply 545 on top of MilSpec. Fill, apply more 545
    8) The old holes you will never fully remove. Whatever you use will grin through after exposure to heat/cold. It's a mast, anything above 2m you don't see that much.
    9) I wouldn't apply 3 coats of 545 on the already painted areas. The thicker the paint, the greater risk of subsequent cracking due to flexing Apply the 3 coats on the bare area repairs only. Apply 1 coat on whole mast to even out colour and to fill in some sanding scratches.
    10) Consider roll/brush for topcoat. You get lots of waste when spraying and you need to mask off more. To be honest the slight brushmark effect you get will hide the damage and old holes more. Your call. Your budget, your quality standard.
    11) don't understand the time problem. Sand everything, blast areas, aludine, milspec, 545 patches in that order. You can blast and alodine and paint in 1 day. no? You can of course sand the mast after the blasted patches. The key intervals are the blasting, alodine and milspec. You should try to complete this in one day.

    best of luck


    ps if anyone tells you you should be better with carbon mast, you can tell them they also corrode at alloy/carbon joins!
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.