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Article :: Moisture Meters
Moisture Meters
Moisture meters have become one of the most important tools in a Marine Surveyors work bag. Moisture meters were first used in the lumber industry and have been adopted by surveyors as a tool to "see" into the FRP laminate.
Even though the scales on moisture meters indicate in a percent of moisture that number can not be relied upon to be accurate. Thickness of the FRP skin, delamination of the FRP skin, surface coatings, the type of core material used and other variables affect the indication. My primary meter is an Electrophysics GRP 33. The scale is also divided into three sectors, dry, moist and wet. Those are the terms I will use in my reports and conversations.
When I use a moisture meter I am looking for inconsistent indications. When the meter indicates dry or even moist over a large area but then suddenly indicates wet or goes off scale high, it is an indication of a problem that should be addressed. The meter is especially useful around hardware that has been mounted to the laminate and the fasteners either poorly bedded or the sealant aged and cracking.
The meter obviously can not be used on exterior decks during or just after a rain, on the hull bottom of a vessel just hauled out of the water and also on some hull bottoms painted with certain anti fouling paints because of the high metal content of these coatings. Black bottom paints seem to affect moisture meters more than other colors.