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Old 28-09-2018, 06:57   #1
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Moisuture readings

Hi all, I am looking at buying a boat and have a very recent survey in hand. I am a little perplexed about the moisture readings. The boat is solid fibreglass (hull AND decks) and has teak decks from 1984. Here are some of the readings, which were taken with a Tramex Skipper Plus:

Hull: 40%-90%
Teak on deck: 10-20%
Deck (no teak): 20-80%

The survey indicates that readings above 90% are conditions for core decay.

Given that there is NO CORE anywhere, are these readings of concern given that there are no visual signs of blistering?

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Old 28-09-2018, 08:17   #2
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Re: Moisuture readings

First I would make sure that there definitely is no coring.

The hull reading may be due to a build up of anti fouling paint etc. that is retaining moisture.

Pick a spot with a high reading, clean it off to bare gel coat, let it dry then retest.

The reading for the teak on the deck seem about right but your deck readings need some follow up if there is no coring I have no idea why they would read that high.

Your surveyor should be able to give you some advice on this!

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Old 28-09-2018, 08:37   #3
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Re: Moisuture readings

Thanks. I will definitely have my surveyor pay extra attention to this. The hull readings are above the waterline and the boat was in the water, so not sure how dry it was. Some of the highest readings were next to the mast step and the dorade boxes.
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Old 01-10-2018, 05:48   #4
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Re: Moisuture readings

I'd be interested in what David Pascoe had to say about moisture readings in f/g hulls.
I've just done a google on "moisture readings f/g hull" and there seems to be some doubts as to their use.

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Old 01-10-2018, 17:11   #5
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Re: Moisuture readings

When we bought our boat the surveyor did moisture readings of the hull and deck ! The hull checked out good, the rudder was just getting a damp reading ! The deck how ever showed moisture in certain areas ! I kept an eye on the decks where the reading was up ! When I got the time to fix the core in those areas was wet, also most to the point of mush, so in my case a moisture meter worked as intended ! Boat was under cover for 6 yrs (medical issues) and the area on the cabin top dried to the point of no reading, now this area shows damp/wet again !
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Old 01-10-2018, 18:44   #6
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Re: Moisuture readings

Im curious as to what boat this is as it is very uncommon to not have core in the deck.

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Old 01-10-2018, 20:31   #7
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Re: Moisuture readings

Moisture meter simply cannot determine percentages of moisture in fiberglass ... period !

Take a look at Moisture Meter Mythology
That hysterical laughter you hear as you sail a way in your "new" boat ..... is the seller.
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Old 01-10-2018, 21:16   #8
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Re: Moisuture readings

Moisture meters ca be fooled. There are also layups that can wick water.

Wicking: our 1984 Camper Nicholson was laid up with the greatest new stuff of the day. Solid glass below water, cored above to the toe rail. Decks cored between teak beams. Teak deck. Added to this, two layers of Kevlar below water and one above.

It happens that Kevlar of the day wicks water. The smallest flaw would let water into the layup where it would travel, accumulate and delaminate the outer 1/2 inch. It took weeks to chase these down, grind and repair. The rudder was a total loss.

Teak: you can’t measure moisture in the deck through teak. In fact, fiberglass deck moisture (in the core) cannot be measured with any assurity through non-skid. The fillers retain water and will give a false reading. Your best, most accurate reading will be from inside. I pinpointed my wet deck cores with the headliner removed. Deck measurements were way wrong.

If you remove teak, you must remove all of the screws, fill and fair all of the holes, apply a fiberglass scrim over all of the deck that covers the former screw holes. Only then can you apply the new finish and non skid. If you strip away a teak deck and screws you can measure the core moisture.
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Old 02-10-2018, 07:10   #9
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Re: Moisuture readings

Another good link:

Understanding the Moisture Meter / Electrophysics CT-33 Photo Gallery by Compass Marine How To at

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