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1977 MAKO 21b Sandblasting Woes

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  • 1977 MAKO 21b Sandblasting Woes

    [img][/img]Hi,

    I purchased this boat from my cousin, which had several layers of bottom paint, which had bare spots and was very rough looking. I found a local man who sandblasts bottom paint, and took it to him. Not knowing what to expect, it looked ok from 20 feet away, but when I got it home, I noticed 75 pinholes on the port side, along with some residual bottom paint remaining in the gelcoat.

    What material should I use to fill these holes, which are mostly just below the waterline? After these are filled, I understand some epoxy ablative coat is supposed to be applied before the bottom paint.

    I have a pier with a boatlift, but would like to keep the boat in the water over a long weekend. Can I get by with skipping the ablative coat and just bottom paint it? The gelcoat has an etched look after sandblasting, so there should be plenty for the paint to adhere to.







    Seth Anderson

    Moon, VA

    1977 MAKO 21b

    1991 Albemarle 24 Express

    1988 Henry O 15' Challenger

    1990 Tremblay 12' Skiff

    1984 Grady White 22' Pacifica (Sold)

    1988 Grady White 22' Seafarer (Sold)

    1990 Grady White 19' Tournament (Sold)
    Seth Anderson[br]Moon, VA[br]1977 MAKO 21b[br]1991 Albemarle 24 Express[br]1988 Henry O 15\' Challenger[br]1990 Tremblay 12\' Skiff[br]1984 Grady White 22\' Pacifica (Sold)[br]1988 Grady White 22\' Seafarer (Sold)[br]1990 Grady White 19\' Tournament (Sold)

  • #2
    Welcome to CM! The ideal method is to epoxy coat the bottom then apply bottom paint. Many smaller boats are just sanded then have bottom paint applied so technically you could do that too but I would want those pinholes fixed as much as possible since they are voids directly to the glass and could form into blisters. If you are only talking about leaving in for a few days it should be a problem since it sounds like the boat would be on a lift and have time to dry out.
    quote:


    Originally posted by drseth


    [img][/img]Hi,


    I purchased this boat from my cousin, which had several layers of bottom paint, which had bare spots and was very rough looking. I found a local man who sandblasts bottom paint, and took it to him. Not knowing what to expect, it looked ok from 20 feet away, but when I got it home, I noticed 75 pinholes on the port side, along with some residual bottom paint remaining in the gelcoat.

    What material should I use to fill these holes, which are mostly just below the waterline? After these are filled, I understand some epoxy ablative coat is supposed to be applied before the bottom paint.

    I have a pier with a boatlift, but would like to keep the boat in the water over a long weekend. Can I get by with skipping the ablative coat and just bottom paint it? The gelcoat has an etched look after sandblasting, so there should be plenty for the paint to adhere to.







    Seth Anderson

    Moon, VA

    1977 MAKO 21b

    1991 Albemarle 24 Express

    1988 Henry O 15' Challenger

    1990 Tremblay 12' Skiff

    1984 Grady White 22' Pacifica (Sold)

    1988 Grady White 22' Seafarer (Sold)

    1990 Grady White 19' Tournament (Sold)


    1978 Mako 25 - Blind Hog
    1985 Mako 20c - sold
    Fort Walton Beach, FL
    http://www.classicmako.com/forum/top...TOPIC_ID=42841

    Comment


    • #3
      Hi.

      I just helped "Goin-Coastal" redo the bottom of his 1998 Mako 333. He had about 180 shallow bottom blisters that we filled after it was blasted. I suggest you use Interlux's "Watertite" two- part epoxy putty to fill the voids. It is a little expensive, but it dries quick and is EASY to sand smooth. Since your bottom has been blasted you MUST(in my opinion) apply an epoxy barrier coat before you apply bottom paint. If you don't you are leaving the surface open to microscopic water intrusion. Make sure your hull is dry and the open blisters are not weeping. I suggest watching videos on YouTube about "fixing boat blisters". I found several had good ideas about how to do it "correctly". Also most videos recommend that you apply your first coat of bottom paint before your last coat of epoxy barrier has finished hardening. Hope this helps.
      Boca Raton, FL[br]Current: 2002 253[br]Former: 1995 19[br]Former: 1979 19b

      Comment


      • #4
        Sandblasting is way too harsh on gelcoat and on fiberglass dry media creates excessive heat when hitting the material being blasted. Recycled glass media is much better, but still can not be dry blasted and should be hydroblasted. Glass blasting media has rounder edges and less harsh, and the water helps cushion against the gelcoat and keeps the temps close to outdoor temps and out of the dangerous temp range of gelcoat.

        Try this link and I detail the process I used when blasting my 21 bottom.

        http://www.classicmako.com/forum/top....&whichpage=24

        D-
        Current Mqko - 1990 Mako 211 w/2006 250 E-TEC. http://www.classicmako.com/forum/topic.asp?TOPIC_ID=6226. [br]- Previous Makos 1987 20C, 1979 23\' IB, 1970s 17 Angler

        Comment


        • #5
          dtmackey is right....ideally you want a wet, dustless, lower pressure blast process. We used crushed glass too. That said, I think it makes barrier coating even more important since the sandblasting was used in this instance.
          Boca Raton, FL[br]Current: 2002 253[br]Former: 1995 19[br]Former: 1979 19b

          Comment

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