what are these spots in my gelcoat?

Discussion in 'Fiberglass and Composite Boat Building' started by naturewaterboy, Aug 9, 2009.

  1. naturewaterboy
    Joined: Sep 2006
    Posts: 211
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: key largo, florida, usa

    naturewaterboy Steel Drum Tuner

    I have some small (most are about 1mm) diameter round "holes" in my gelcoat, all on the sides of the boat, at or below the waterline. I stripped the bottom paint off the hull, sanded a little with 80 grit and found these all around the boat. They seem to be more on one side of the boat than the other. They are not very deep - they don't seem to go thru to the glass - maybe 1/2 mm deep or less. Any ideas what they are, and are they a problem? :?:
     

    Attached Files:

  2. ondarvr
    Joined: Dec 2005
    Posts: 1,411
    Likes: 45, Points: 48, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    How did you strip the bottom paint off?
     
  3. mark775

    mark775 Guest

    Imperfections/ foreign matter in the gelcoat that you sanded "a little" through. One of the spots (green) looks to be the color of PVA (polyvinyl alcohol) used as a parting agent. The blue, I don't know. I believe that the builders were a little sloppy but also that you were too aggressive sanding.
     
  4. naturewaterboy
    Joined: Sep 2006
    Posts: 211
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: key largo, florida, usa

    naturewaterboy Steel Drum Tuner

    On the sides, I just sanded with a 6" Festool DA sander in the rotary mode. It doesn't sand in a pure, rotary pattern like a grinder does, it wiggles around a little. I'll look closer at the color of the spots. The blue is probably bottom paint.
     
  5. ondarvr
    Joined: Dec 2005
    Posts: 1,411
    Likes: 45, Points: 48, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    They most likely scraped barnacles off the hull and then bottom painted it, they can take chunks of gel coat off.
     
  6. Boatpride
    Joined: Oct 2008
    Posts: 37
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: UK

    Boatpride Boatpride

    Once barnacles take hold, they bore through the gelcoat into the fiberglass - if unchecked. They get more and more secured. So when its time to remove them, then as Ondarvr suggests the gelcoat comes away in chunks.

    If you would like to read a post on fixing gelcoat follow this link

    Gelcoat Repair

    Hope that helps!
     
  7. naturewaterboy
    Joined: Sep 2006
    Posts: 211
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: key largo, florida, usa

    naturewaterboy Steel Drum Tuner

    I am repairing the bottom with epoxy resin, so I'll fill these with some epoxy, as it is all going to get painted with Interlux 2000E barrier coat and then a bottom paint - probably Petitt Vivid Eco. Thanks for the answers - the holes probably are from barnacles, as the bottom paint was pretty well gone when I bought the boat, and it had a lot of hard growth on it.
     
  8. mikereed100
    Joined: Jan 2007
    Posts: 87
    Likes: 4, Points: 0, Legacy Rep: 33
    Location: Borneo/California

    mikereed100 Junior Member

    Possibly styrene that was incompletely mixed with the gelcoat?

    Mike
     
  9. mastcolin
    Joined: Jun 2005
    Posts: 146
    Likes: 13, Points: 0, Legacy Rep: 150
    Location: The Netherlands

    mastcolin Senior Member

    Bubbles in the spray-on gelcoat?

    They were closed till you sanded?

    Fill them with epoxy, paint.

    Have you checked the hull for moisture content? Not that it can necessarily mean anything but if it is very high and you put on the epoxy system you may encourage osmosis later in life.

    ps so the holes maybe the gelcoat osmostically breaking down for the reason given previous - pva, stryrene, bad mix, too much catalyst
     
  10. naturewaterboy
    Joined: Sep 2006
    Posts: 211
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: key largo, florida, usa

    naturewaterboy Steel Drum Tuner

    I haven't checked the hull for moisture, but it has been sitting on land for 5 years, and I've had a tarp rigged up for shade over the boat for the last two. It also keeps most rain off the boat.
     
  11. Herman
    Joined: Oct 2004
    Posts: 1,615
    Likes: 87, Points: 0, Legacy Rep: 1240
    Location: The Netherlands

    Herman Senior Member

    OK, so we have:

    -barnacles
    -unmixed styrene
    -bubbles in gelcoat (less likely)

    I would like to add:
    -unmixed drops of peroxide in gelcoat. (malfunctioning spray equipment).

    That can also be the cause. However, both unmixed styrene, mek or peroxide, or bubbles, are likely to cause problems on the surface directly after demoulding, so at least should have been taken care of by the manufacturer.

    Luckily solving this problem is not difficult nor expensive.
     
  12. Wynand N
    Joined: Oct 2004
    Posts: 1,255
    Likes: 145, Points: 73, Legacy Rep: 1806
    Location: South Africa

    Wynand N Retired Steelboatbuilder

    contamination is my guess and it looks suspiciously like some moisture was present in the compressor/pipes when spraying the gelcoat.

    Funny, we sprayed some epoxy paint this week on the deck of a 6 meter daysailor with the same symptoms - left small patches of pin holes holes at places on the primer that will not cover.
    Found out the guys did not drain the compressor for a couple of days and after doing so, the problem disappeared.
     
  13. Herman
    Joined: Oct 2004
    Posts: 1,615
    Likes: 87, Points: 0, Legacy Rep: 1240
    Location: The Netherlands

    Herman Senior Member

    Forgot about moisture indeed.

    On all your machines, have a moisture trap installed, and get the one that drains automatically.

    When spraying with a spraygun, have a moisture trap (and pressure regulator) as close to the gun as practical.
     
  14. ondarvr
    Joined: Dec 2005
    Posts: 1,411
    Likes: 45, Points: 48, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    They don't look like water or catalyst drops, Water leaves round pits, catalyst will leave soft spots that will deform the surface. These look like chunks that were removed from something sticking to the surface.
     

  15. naturewaterboy
    Joined: Sep 2006
    Posts: 211
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: key largo, florida, usa

    naturewaterboy Steel Drum Tuner

    It probably is attack from marine organisms - probably barnacles - as the bottom paint pretty well gone in around the waterline when I bought it. Thanks to everyone for your ideas.
     
Loading...
Similar Threads
  1. tomherrick
    Replies:
    29
    Views:
    2,886
  2. LeRi222
    Replies:
    10
    Views:
    6,610
  3. Capt. Chris
    Replies:
    2
    Views:
    1,268
  4. tuantom
    Replies:
    1
    Views:
    1,218
  5. LEASEGUY
    Replies:
    13
    Views:
    7,251
  6. eusscmp
    Replies:
    6
    Views:
    9,534
  7. weldandglass
    Replies:
    30
    Views:
    1,083
  8. burke
    Replies:
    2
    Views:
    412
  9. guam2250
    Replies:
    8
    Views:
    820
  10. jonboy834
    Replies:
    8
    Views:
    1,403
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.