what are these spots in my gelcoat?

[naturewaterboy]

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? :?:

[ondarvr]

How did you strip the bottom paint off?

[mark775]

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.

[naturewaterboy]

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.

[ondarvr]

They most likely scraped barnacles off the hull and then bottom painted it, they can take chunks of gel coat off.

[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 (http://boatpride.com/fiberglass-boat-repair-and-sailboat-painting/gelcoat-repair.html)

Hope that helps!

[naturewaterboy]

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.

[mikereed100]

Possibly styrene that was incompletely mixed with the gelcoat?

Mike

[mastcolin]

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

[naturewaterboy]

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.

[Herman]

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.

[Wynand N]

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.

[Herman]

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.

[ondarvr]

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.

[naturewaterboy]

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.