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Old 24-02-2012, 14:47   #16
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Re: Need Help on Hull Construction

If your boat had bottom paint on it and gel coat..it could be in a heated building for 2 years and not dry out.

If you put epoxy barrier coating on over wet laminate and ge coat...there's a VERY GOOD chance you may CAUSE blistering because there could be osmotic pressure building and now no way for any to escape (from what I have been reading).
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Old 24-02-2012, 20:42   #17
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Re: Need Help on Hull Construction

You need to find a surveyor and yard who have some idea what they are talking about. If, as you said earlier, the moisture readings were made on antifouling bottom paint, then the person making them has no idea what they are doing. You cannot take moisture meter readings on bottom paint. The bottom paint must first be completely removed. Antifouling paint will give false positive readings every time.
Most moisture meters work by measuring the relative conductivity of the material in question, which is why moisture meter readings are relative and taken on multiple scales, ie a wood scale and an FRP scale. Because wood has different base conductivity than fiberglass. Obviously any metals in the substrate will read as moisture, as metals are much more conductive than fiberglass or wood. Antifouling bottom paint has copper in it, which is highly conductive on a relative scale. Hence the false positives. Any surveyor should know this, as should any yard. I would not let anyone who didn't know this work on my boat in this regard.
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Old 24-02-2012, 21:04   #18
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Re: Need Help on Hull Construction

Correct Minaret except the meter reads capcitance. Moisture, metals, mineral fillers all set them off and bottom paint has it all.

Most surveyors seem to use this one from Electrophysics. I finally bought my own. Understanding the Moisture Meter / Electrophysics CT-33 Photo Gallery by Compass Marine at pbase.com there is a pretty good discussion at this site. I too found high variability on my deck. Wet from outside and dry from inside but the deck has fillers and non-skid. The inside is unpainted fiberglass and dry. To check, I used a hole saw to inspect the core from inside. Inside reading were spon-on. The deck 1/2 inch away says wet. This understanding & meter saved me a bushel of boat bucks as I didn't need to recore.
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Old 25-02-2012, 04:55   #19
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Re: Need Help on Hull Construction

Quote:
Originally Posted by minaret View Post
You need to find a surveyor and yard who have some idea what they are talking about. If, as you said earlier, the moisture readings were made on antifouling bottom paint, then the person making them has no idea what they are doing. You cannot take moisture meter readings on bottom paint. The bottom paint must first be completely removed. Antifouling paint will give false positive readings every time.
Most moisture meters work by measuring the relative conductivity of the material in question, which is why moisture meter readings are relative and taken on multiple scales, ie a wood scale and an FRP scale. Because wood has different base conductivity than fiberglass. Obviously any metals in the substrate will read as moisture, as metals are much more conductive than fiberglass or wood. Antifouling bottom paint has copper in it, which is highly conductive on a relative scale. Hence the false positives. Any surveyor should know this, as should any yard. I would not let anyone who didn't know this work on my boat in this regard.
Not sure about the surveyor...why do you need one at all?... but agree with the yard if you are not going to do the work yourself.

You have to find a big refit yard such as the one you work for...too many yards that have "done a lot" of blister jobs...probably have just done them wrong and were either lucky or time will tell.
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Old 25-02-2012, 07:01   #20
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Re: Need Help on Hull Construction

Thanks again, most helpful, specially the link for the moisture gauge.

I am really getting an education here...
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