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Old 14-03-2014, 10:41   #1
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Osmosis Question

Hiya all

I am near to having a boat surveyed and have been wondering about the moisture testing that is done. I have had it done a few times over the years but always on a boat that was in the water and then lifted for a test.
this time however this boat has been out and on the hard for months.
Will I need to have it put in the water for a few days and then taken out and tested or doesn't it matter ?

Thanks
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Old 14-03-2014, 10:48   #2
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Re: Osmosis Question

Leave it where it is
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Old 14-03-2014, 11:20   #3
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Re: Osmosis Question

Moisture Meter Mythology
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Old 14-03-2014, 11:24   #4
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Re: Osmosis Question

no reaason to get it wet... that's where false readings come from. You want to find a bare spot without bottom paint though I think. You situation is perfect to tell if it has real water in the hull.
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Old 14-03-2014, 16:01   #5
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Re: Osmosis Question

Thanks guys
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Old 15-03-2014, 00:09   #6
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Re: Osmosis Question

When I had my boat surveyed before buying, the surveyor did a moisture test, showed no problems. The boat have osmosis big time.
So in my humble experience, the moisture measurement won't tell you anything about osmosis. Look for blisters, if not present then the boat most likely don't have osmosis.
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Old 15-03-2014, 00:15   #7
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Re: Osmosis Question

Not entirely true, some boats that are wet are not blistered yet.
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Old 15-03-2014, 01:52   #8
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Re: Osmosis Question

I suppose it depends on how deep into the paint/gelcoat/poliester the measurement is taken from.
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Old 15-03-2014, 07:50   #9
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Re: Osmosis Question

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When I had my boat surveyed before buying, the surveyor did a moisture test, showed no problems. The boat have osmosis big time.
So in my humble experience, the moisture measurement won't tell you anything about osmosis. Look for blisters, if not present then the boat most likely don't have osmosis.
First of all I don't like the word "osmosis" as it means different things to different people but otherwise I agree with you.

FRP is not water proof, it is hydroscopic.

Elevated moisture levels are not a predictor of blisters. I've metered thousands of boats and seen hundreds of boats with high moisture levels and no blisters.

On the other hand blisters are unpredictable. My own boat went for 35 years with no blisters then suddenly developed hundreds of them in one season.
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Old 15-03-2014, 07:53   #10
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Re: Osmosis Question

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I suppose it depends on how deep into the paint/gelcoat/poliester the measurement is taken from.
The capacitance type meters used by surveyors all read from the surface. While different meters will read to slightly different depths, that cannot be controlled.

I suspect you are thinking of resistance type pin meters that require small holes to be drilled. Few FRP boat owners will allow this.
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Old 15-03-2014, 08:11   #11
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Re: Osmosis Question

So, does it matter if the boat hasn't been in the water for a year before the test is done ??
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Old 15-03-2014, 08:45   #12
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Re: Osmosis Question

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So, does it matter if the boat hasn't been in the water for a year before the test is done ??
That's actually a good scenario for a more accurate reading.
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Old 15-03-2014, 09:04   #13
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Re: Osmosis Question

The problem is not blisters. Blisters are a symptom. The problem is water dissolving the Resin. Have a full laminate profile done. Understand how the boat is layed up, what resin was used. Are other boats having issues with water saturated laminates or showing symptoms of resin loss?
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Old 15-03-2014, 09:16   #14
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Re: Osmosis Question

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The problem is not blisters. Blisters are a symptom. The problem is water dissolving the Resin. Have a full laminate profile done. Understand how the boat is laid up, what resin was used. Are other boats having issues with water saturated laminates or showing symptoms of resin loss?
The process of dissolving resin is called hydrolysis. Having a laminate profile performed requires taking a plug from the hull with a hole saw. Even if you do take a plug the results will tell you only what is happening in that 2" circle and does not apply to the rest of the hull.

Blisters are almost always a cosmetic condition in or just under the gelcoat. However, if there a a brown liquid emanating from a blister and it tastes slightly acidic, that is hydrolysis (dissolving resin). This could be a more serious issue depending on extent and where it appears in the laminate schedule. The answer to everything in this subject is ...... it depends.
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Old 15-03-2014, 09:24   #15
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Re: Osmosis Question

But the blister did not just appear with out cause. My guess is the resin did something to push out a blister. You can get a decent water egress profile by grinding into the finish layer. Not necessary to core the hull.
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