Wednesday, September 28, 2011

Keel and Bottom Work Procedures

Keel and Bottom Work Procedures

The Complete Procedures:

  • Keel Preparation: Stripping the Keel
    • There is no easy way to do this, unless you have access to and permission from the boatyard to use a sandblaster. This would probably require you to tent off the boat.
    • Cover the ground and use vacuum hoods on power tools for environmental reasons.
    • Chip and scrape as much as possible with an old chisel and stiff scraper, being careful when you are working near the joint and fiberglass stub.
    • Using an angle grinder (with dust hood) and sanding disks, sand off as much as possible. This step will take the longest and remove the vast majority of the remaining material.
    • Using and angle grinder with a course wire wheel clean up what remains and try to get to bare metal wherever possible. Make sure you remove all rust.
    • Immediately before applying the epoxy barrier coat, do a quick but thorough sanding with an orbital sander and course paper (30-40 grit) to take off the inevitable (and unseen) oxidation that begins immediately when iron is exposed to oxygen.
    • Dispose of collected material properly -- whatever that means. In my case, I collect it in a 5 gallon bucket and dispose of it when our local county landfill collects hazardous waste.
  • Keel: Applying the Barrier Coat
    • The steps below must be done quickly as oxidation is occuring while you wait.
    • Having removed the flash oxidation with the sander, clean surface of dust with tack rags.
    • Wipe the entire surface with acetone to remove oils and water.
    • While the acetone is drying, begin to mix your unthickened epoxy. Mix thoroughly!
    • Apply epoxy to a small area (2 sq feet or so) with a foam brush or roller, being sure to get into all the pits and crevices.
    • Scrub the area with a wire brush to increase the epoxy's contact with the metal. 
    • Tip off the wire brush marks with vertical, then horizontal brush strokes.
    • Repeat the last three steps until the entire keel is coated.
    • Subsequent coats may be applied right away, as long as the epoxy hasn't cured completely. Otherwise before applying the next coat you will need to scrub off the amine blush with a green scotch pad and dry if off, being sure to collect all the waxy blush residue.
    • As you go through this process and the epoxy begins to cure be sure to keep an eye out for drips and sags. Unthickened epoxy, especially on a hot day, is VERY runny.
    • After two or three coats, begin to fair the pits and crevices with epoxy thickened with your favorite fairing compound. (I use west systems 407 as it sands easily but still has some structural strength to it). Let fairing coat dry.
    • Sand your fairing coat smooth and clean the surface with tack cloths and acetone as before. Recoat with unthickened epoxy. Note: if there are really deep pits you may have to do this a couple of times to fill the holes.
    • You will need a total of 5-6 coats of epoxy to thoroughly protect the iron from oxidation and galvonically isolate the iron from the copper in the bottom paint. Remember to wash the amine blush off the surface before painting.
  • Sealing the Keel to Hull Joint
    • Scrape out as much of the old sealant as you can reach with your favorite pointy tool.
    • Clean the area in and around the joint thoroughly -- no dirt, no oil, no rust.
    • Douse the joint in acetone to remove moisture that may linger deep within.
    • Tape off both sides of the joint to ensure a neat edge. (This allows you to be really sloppy with applying and smoothing the new sealant.)
    • Using 3M 5200 and a caulking gun, apply a thick bead of sealant along the joint. Be sure to squeeze as much sealant into the joint as you can.
    • Smooth off the sealant while it is still wet and sticky (wear latex gloves!)
    • Remove masking tape and allow sealant to dry (up to 7 days)
  • Fairing the keel to hull joint.
    • Take this advice/procedure with a grain of salt. As iron is obviously not flexible and fiberglass is, I suspect there is some flexing in the joint. Fairing over the joint with thickened epoxy thus has two problems; if the hull flexes at the joint the epoxy will crack, and I am not sure how well epoxy will adhere to the 3M 5200.
    • If you fair the areas above and below the joint only, you would be able to monitor to state of the joint at every haul out. If you cover it, who knows. The down side is it will not look or perform as well as covering the entire joint.
    • My (unproven) solution to this dilemma was to use West Systems GFlex epoxy, thickened with fairing compound to cover the joint and blend the keel seamlessly into the hull.
    • The procedure is identical to the fairing process above.
(Although there is not much you can do about the area where the keel is resting on the blocks -- unless you want to pay the yard to hoist the boat on the lift while you work on those areas. That can get really pricey as the yard will charge by the hour for the use of the lift.)

I won't go into detail about how to paint the bottom as this is covered extensively elsewhere online.

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