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Old 16-03-2008, 17:23   #1
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white spots on hull?

hello everyone. I just got done stripping the old bottom paint of our boat and saw some spots unde the gelcoat that looked like random white spots. Our hull is blue so you can easily see this. They are not round but more amebia shaped. All random shapes about the width of a dime? Is this normal? or should it be something we should be conerned about?
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Old 16-03-2008, 22:21   #2
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Can you show us a photo of it??
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Old 17-03-2008, 23:38   #3
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I will take one soon and post it. thank you
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Old 30-03-2008, 14:59   #4
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I went to the boat today and I took a picture. Here it is
That is just a small section of the bottom. I took the picture really close to the hull.
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Old 30-03-2008, 19:01   #5
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Most likely some localised osmosis. If the hull has been dry for more than a day or so they show up like nthis.
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Old 30-03-2008, 21:21   #6
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it has been out of the water since october. is this normal? anything i should be worried about?
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Old 30-03-2008, 21:26   #7
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Obviously it will pay to have it examined by a fibreglass boat builder to confirm it is osmosis (very hard to diagnose from a photo) If it is and it was my boat I would simply grind out the spots, dry them well (tent the area and use fan heaters) and fill with epoxy and monitor whenever you haul the boat. Osmosis shows up as small blisters when the boat is wet so it pays to waterblast as soon as possible after hauling and check the hull over whilst still very wet. After it starts drying it takes a while before it shows up as these spots.
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Old 30-03-2008, 22:59   #8
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It may be, and probably is, osmosis.

What ever you do, get opinions from someone OTHER than a boatyard fiberglass repairer.
They make a fortune in scaring the daylights out of boat owners who then part with lots of money, all to no avail. I have then seen the problem, re occur. Repairers will NEVER put a guarantee on there work repairing osmosis. WHY?

I have seen osmosis on one side of a hull and yet no sign of it on the other. Sailing in warm waters does seem to bring the "problem" out sooner.
Osmosis is very common in ALL fiberglass boats as well as fiberglass swimming pools and spas, but it is cosmetic only. The boat will NEVER leak because of osmosis.
It does NOT lead to the boat loosing structural strength, EVER.

It will reduce the resale value of your boat, so fix it just before you sell the boat, and not before.
It is generally caused by having too much stryene in the fiberglass layup. (which is impossible to control)
It is impossible to build a boat in fiberglass without the possibility of getting osmosis at some stage. Vinylester resin is not the answer either.

I compare osmosis to have fine cracks occur in concrete paving, yes it does occur, can you do anything about it, NO.

I know, I have built many hundreds of fiberglass boats swimming pools and spas.

Osmosis does not occur with epoxy resin only Polyester resin.
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Old 31-03-2008, 01:03   #9
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Hmmmm, it's a heck of a lot of little white spots though. And they aren't really spots, Some seem to meld to another. I am wondering if this is simply the "cement" left behind by little creatures gluing themselves to the hull and as the hull has dried out now, they show up as this splodgy stuff. I am thinking those little worm fellows that have the little cement casting that goes all over the place. If the hull was waterblasted, it will remove the casment, but it will never clean completely off the hull.
Here's the way to test it. If you sand a very small area lightly, the cement stuff will come right off. If it is Osmosis, the spots will not come off. It will be in much deeper.
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Old 31-03-2008, 06:07   #10
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Those look like spaghetti worm tube attachment points to me. The walls of reef aquarium look just like that after I run magnetic scrubbers over the glass.
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Old 31-03-2008, 12:30   #11
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spaghetti worm tube attachment
I that what they are called. Yes that sort of creature is what I was thinking of.
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Old 31-03-2008, 14:11   #12
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What does your boat yard manager say? He in all likelihood has seen this at least a dozen times before.
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Old 31-03-2008, 22:04   #13
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I am always at the boat on sundays an no one seems to be around when I go. (realli early). These spots are under where the bottome paint was. the red spots are areas where the bottom paint didnm't come off all the way. and the horizontal lines are from the scrapper.
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Old 05-04-2008, 02:46   #14
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Is there any softness in the areas, osmosis is the water absorbsion of the glass fibre.
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Old 06-04-2008, 00:44   #15
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there is no softness at all. it feels and sounds the same as a part of the bottom that does not have it. i would say a good 65% of the bottom is like this.
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