CORE Moisture Evaluation - How should I Fix the Issue

[cruisingmom]

During the survey and subsequent moisture meter evaluation it was noted that the cabin roof of my Whitby 42 had high moisture. I used the meter to plot out a rough area and then began drilling 3/8 inch holes to find the areas of wet core. It seems that poorly designed dorade boxes were my main cause of moisture ingress (sure under the hardware there was also moisture but pretty localized to the bedding area. So, I found a 2ft by 4ft area around the dorade box and used my circular saw to cut the outline of the area with the intent of pulling up the top skin and digging out the wet core. Unfortunately the skin is still fully bonded to the only slightly wet core so I can't pull it up. Now I am not sure whether I would be better off leaving the skin down and just cutting out the dorade box (1ft by 8 in) and drying out the core using alcohol and acetone. Please - I would greatly appreciate some input and suggestions here = only at the dorade thru hull (inside the box) was the core completely gone - all other areas the core was still fiberous when spun out with a nail and only in a couple of localized areas was it really discolored from tan to brown.
If I tear off the skin I will destroy the integrity of the polyester glass composite by fracturing it. I live in Maine so cold weather is coming and I don't want freeze damage either. Responses soon would be greatly appreciated.
Andy

[Maine Sail]

Andy,

I would not try to salvage that skin. It's actually easier to bevel the edges to a 10:1 taper and re-lam with new balsa.

To remove the top skin, if still bonded well, you'll want to cut it into small squares. the length of the Fein multimaster tools blade. With a tool like a Fein Multimaster this job becomes much easier. Once you've cut a pattern of small squares then dig under it with the Fein, at a low angle, to remove each small square of top skin. Time consuming yes but you won't run a high risk of fracturing the inner core by ripping the to skin off. The top skin is almost always thicker than the botto skin so be careful. Once the top skin is off you can use the Fein with the scraper blade to romove the bulk of the balsa from the bottom skin the a drill with brass brush or sand paper or similar to get the rest.

Drying wet balsa rarely if ever works even with holes drilled. Remove and re-lam is the best SOP.

Great seeing you the other day. I am still interested in those binocs and will call you when I get home from this business trip.

[cruisingmom]

It was great seeing you too.
I looked up what a Fein Multimaster tool was and I can see why you recommend it. When I drilled and spun out the core from the evaluation holes, in most areas the core appeared fiberous and light colored with only a slight moistness to touch. I even saved samples of each type of core response to verify the degradation of the fibers. In only a couple of locations was the core fibers discolored (brown to dark brown) and in the 2 dark brown areas the core was still somewhat fiberous - more matt like and wetter. So my question relates to how wet is bad. Is it that if there is any moisture in the core it is bad and will eventually rot? Or is it possible to localize the problem (like the poorly designed dorade boxes - root of the issue) and cut these sections out. I was unable to even peel an edge up with a chisel on the corner of the top skin over a slightly damp section (no discoloration but not completely dry)? As I think I stated, the dorade boxes were improperly designed and installed and were the root I believe of the moister ingress. My questions are for understanding and not validating my desire not to rip the skin off. Thanks
Andy

[tommays]

When searching for boats this season ALL the older boats had moisture in the decks. BUT did not have soft spots or seem to need immediate attention

The question is how the boats going to be used as on a 35' boat we race on most of the deck was recored, on the other hand if your just kicking around the local area it may not be as serious of and issue

[Maine Sail]

Andy,

I think too much is made of "wet decks" all to often. As we discussed the other day many surveyors have never even seen the internal results of what a 30%+ reading looks like on a JR Overseas moisture meter.

If I find wet readings I sound them very carefully. The soundings will often tell you more about core condition than will a simple moisture reading on its own. The two must always be combined to make an educated decision on whether to repair or leave it alone.

If the core still sounds out similar to an area that is known to be dry, simply stop the ingress of water and leave it alone if it's in a non-critical area. A dorade box on most boats is usually a non-critical load area and if it sounds out fine but has higher than normal readings then I'd personally leave it and continue to monitor it with soundings and moisture readings..

Areas around stanchions, masts, chain plates, cleats and bulkheads are under loads than an area under a dorade box and are areas I would address asap if they did not sound out well and gave dull thuds..

Usually when the meter pegs, this is considerably higher than a 30% reading, you will find the balsa to begin to be discolored. If it has been saturated long enough it will look like coffee grounds but will feel mushy under foot as well. Even when damp to moderately wet the balsa will still be well bonded. There are very few boats out there without some areas of wetness.

You can do wither two things here. 1) remove and re-lam the top skins and fix it well or 2) Fill and fair over the holes you've made and live with it. If it was me I'd want to re-lam after I'd gone this far.

If you need to borrow my Multi-Master let me know via PM. I'll be home from this business trip on Sat. All I ask is that you bring it back with good working sharp blades..