I have previously paid for two surveys on two Catalina 25's. One surveyor used a moisture meter on the deck, which has a non skid pattern in it. The other surveyor used a plastic mallet and banged on the deck to listen to the sounds. He said a moisture meter isn't accurate on non skid decks. Who was correct? I suspect it was the surveyor with the moisture meter, as the other one didn't use one even on smoothe surfaces like the hull, or the transom. What do you say? Thank you.
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The one with the mallet was correct .......
Moisture meters only measure the 'surface moisture' in a laminate. Moisture meters are rarely 'calibrated'. That surveyor with a mallet was looking for delamination and in a cored structure also underlying rot. Such a procedure is looking for already developed destruction. All fiberglass is water permeable to some degree so a high moisture reading may be 'normal' water absorbtion. A high moisture reading from a meter only means surface moisture .... but 'may' indicate inappropriate water absorbtion due to hydrolysis or other ongoing 'destruction' that is deeper inside the laminate. A well made laminate structure of the proper proportions of resin and glass, etc. etc. that doesnt have 'discontinuities' may be totally saturated with water with no ill effect. I'd trust the guy with the mallet long before I'd trust a 'moisture meter'. A moisture meter can only be a 'corelation' to the laminate condition; otherwise, the ONLY way to know is to perform a destructive 'core sample' (then send to a laboratory, etc.) in those areas of suspicion. That said, a zone of high mosisture near a stancheon or shroud on the deck or other hardware probably indicates that the core underneath the laminate is rotting, etc.
Moisture meters only measure the 'surface moisture' in a laminate. Moisture meters are rarely 'calibrated'. That surveyor with a mallet was looking for delamination and in a cored structure also underlying rot. Such a procedure is looking for already developed destruction. All fiberglass is water permeable to some degree so a high moisture reading may be 'normal' water absorbtion. A high moisture reading from a meter only means surface moisture .... but 'may' indicate inappropriate water absorbtion due to hydrolysis or other ongoing 'destruction' that is deeper inside the laminate. A well made laminate structure of the proper proportions of resin and glass, etc. etc. that doesnt have 'discontinuities' may be totally saturated with water with no ill effect. I'd trust the guy with the mallet long before I'd trust a 'moisture meter'. A moisture meter can only be a 'corelation' to the laminate condition; otherwise, the ONLY way to know is to perform a destructive 'core sample' (then send to a laboratory, etc.) in those areas of suspicion. That said, a zone of high mosisture near a stancheon or shroud on the deck or other hardware probably indicates that the core underneath the laminate is rotting, etc.
Moisture meters
FRank, the term mopisture meter is kind of a misnomer. They actuall measure density rather than moisture. A good surveyor will use both a hammer and a meter. The hammer is often the primary means and if the surveyor finds a soft spot. ( Tht awful dead sound) they will use a meter to verify it. Last spring I spent two days with about 30 other surveyors using a variety of meters and hammers on derilect boats. Some places the meters showed wet we drilled two inch holes to find they were dry and vice versa. I have never heard of a meter not working on non-skid. I have picked up bad areas with one. Alot of it has to do with experience and knowledge about meters. They are another tool to be used.
FRank, the term mopisture meter is kind of a misnomer. They actuall measure density rather than moisture. A good surveyor will use both a hammer and a meter. The hammer is often the primary means and if the surveyor finds a soft spot. ( Tht awful dead sound) they will use a meter to verify it. Last spring I spent two days with about 30 other surveyors using a variety of meters and hammers on derilect boats. Some places the meters showed wet we drilled two inch holes to find they were dry and vice versa. I have never heard of a meter not working on non-skid. I have picked up bad areas with one. Alot of it has to do with experience and knowledge about meters. They are another tool to be used.
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