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Old 16-05-2013, 09:54   #1
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Wet core, CT-33 moisture meter, and me

Hi:

This is my report on using the CT-33 moisture meter and drying out my core in several places. I think I have something novel to report.

The meter works great. Any time it has read 30 to pinned, upon drilling a hole I found loose water, so the core was past the fibre saturation point. Away from the high readings around most of the stanchion bases and other water ingress places it reads about 5 to 10. There is a nice slope in the readings as I transition between a known wet spot and an (assumed) dry 6-10 reading area. All my hole drilling and inspection of what comes out tracks very well with what the meter tells me, as do percussion soundings.

Frankly for the $200 some dollars these things cost, every boat owner with a cored boat should own one. The only problem I had was that the meter scale came unglued, buckled up and stopped the meter needle. A bit of super glue and swearing fixed that.

I have about 10 areas each of 2 to 3 square feet that are wet. Many would likely have cut out the areas, dug out the core and put the old piece back in, but I opted for the drill holes on 1 inch centres approach. It is a lower skill but brute force approach, and a good chance it will even take longer for the average person. I did this for a number of reasons. I figure though reattaching skins is not that hi tech, there is enough art to it that I would have trouble getting things back in plane again, for the same reasons that I can't lay floor tile well (BTDT, trip over the high spots). My brain does not do art, I can barely sign my name, and any actual handwriting is illegible, even to me. Plus, my boat is under a frame and clear tarp, so there just isn't adequate room to work with anything much bigger than a syringe filled with epoxy.

Now we come to the novel part. How to encourage the core to dry? There are just too many areas and too little electrical feed to consider electric heat of any sort. Plus I don't want to pay $10 a day for months to dry things.

The first part is being under a clear tarp, and this does a great job of getting the deck air temperature 30 degrees F above ambient in full sun (which thus far wasn't often this year). However, placing hand upon deck does not feel particularly warm, all white and reflective and all.

Next my thoughts turned to maybe painting the areas black, but I didn't relish the thought of having to remove whatever paint I used. How about black fibreglass window screen? Not enough black there, weak contact to the boat, and expensive.

Then it came to me ... black duct tape. Two $8 rolls, a bit of time poking out all the holes so the moisture can escape and bingo. The meat thermometer (Don't report me to my wife for a kitchen utensil infraction) read about 100F inside one of the holes one day (ambient 60 to 70, no actual measurement recorded), and the areas feel very warm to the touch. About 5 in the afternoon one day, I taped a piece of clear plastic to a small area to seal in any escaping moisture, and 2 hours later, I could see a condensation pattern over the holes on the plastic. Moisture has left the building.

The first area was done about 3 or 4 weeks ago and has probably seen about 10 full sun days, and a few partly sunny. The high reading at the start was over 30, but not pinned, and now reads about 28. Some of the more marginally wet areas that started at 15 to 20 are now in the 10 to 15 range. I take readings about 9AM, after any dew has evaporated, but the sun isn't working its magic yet. Late day readings tend to all be 30 everywhere as I believe the moisture is driven to the surface by the heat of the sun. I only take a reading about every week or so, as the day to day readings just got lost in experimental error - I could not detect any differences over such a short time interval.

I will report back in another month or so.

I hope someone finds this interesting.

Cheers,

Boulter
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Old 16-05-2013, 10:21   #2
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Re: Wet core, CT-33 moisture meter, and me

Very interesting. So you are drilling holes in the top of the deck? why not below deck? Gravity may be your friend. Below deck holes or vacuum pump may help. Or put an airconditioner or dehumidifier on in the boat for a couple months creating realy dry air. I'm surprised just heat is making moisture go away much. In the end, even if you have the moisture out.... question is... will your core be bonded or mush? It's not the water that's the problem, it's the delamination or dmaage to the core that's the problem..... I guess if you do get it dry in there somehow, you could inject epoxy.
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Old 16-05-2013, 10:51   #3
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Re: Wet core, CT-33 moisture meter, and me

Quote:
Originally Posted by Cheechako View Post
Very interesting. So you are drilling holes in the top of the deck? why not below deck? Gravity may be your friend. Below deck holes or vacuum pump may help. Or put an airconditioner or dehumidifier on in the boat for a couple months creating realy dry air. I'm surprised just heat is making moisture go away much. In the end, even if you have the moisture out.... question is... will your core be bonded or mush? It's not the water that's the problem, it's the delamination or dmaage to the core that's the problem..... I guess if you do get it dry in there somehow, you could inject epoxy.


Yup, once balsa gets wet you can't just dry it out like a foam core. It's physical properties have been changed, and just because its dry doesn't mean it's not rotten. Injected epoxy will be heavy and very brittle, a bad feature in a deck. Lot of work for an inferior repair. Fixing all the holes will take much longer than fixing a strategically placed seam.
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Old 16-05-2013, 22:02   #4
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Re: Wet core, CT-33 moisture meter, and me

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Originally Posted by minaret View Post
Yup, once balsa gets wet you can't just dry it out like a foam core. It's physical properties have been changed, and just because its dry doesn't mean it's not rotten. Injected epoxy will be heavy and very brittle, a bad feature in a deck. Lot of work for an inferior repair. Fixing all the holes will take much longer than fixing a strategically placed seam.
Hi:

I appreciate all the advice that experts such as yourself provide here. The problem is for someone like me is that experts don't agree, so I am left grappling for what to do. It is so easy to just let paralysis set in as I hunt for the "best" solution. At some point I have to halt the research and do something.

One expert has indicated that drill and dry is feasible, and one has indicated it is not. If I had my boat in a building as you likely do in your professional work, or if I lived where it didn't rain every second day, or wasn't still going under freezing some nights such that I didn't need the boat under tarp cover, I could have weighed your recommended technique higher in my thinking.

Unfortunately, I don't possess good conditions. The battery box I molded today is curing in the blistering heat of 54 degrees F in my shop tonight, and as I write, the outside temperature is 40F. It actually warmed up a bit today in comparison to the last 3 or 4 days.

Of my 30 square feet of wet areas, I drilled and dug out about 4 square feet of clearly dark rotted junk.

Next there are areas that were discoloured, but not flat out mush, maybe 10 square feet like this, mostly the coamings. I concede that these areas are weakened. There is a good chance I will put a layer of glass here as there is decorative teak on top that the SO wants back on. (I'd rather leave it off frankly, just a PITA). The percussion test sounds pretty good here though.

Finally, about half of the wet area in the 30 SF under consideration initially returned a reading of 15 to 25, and had a nice bright white colour when drilled out. I do not believe these areas have been wet enough long enough to be seriously impaired, or likely impaired at all.

Perhaps you could expand upon, "Yup, once balsa gets wet you can't just dry it out like a foam core. It's physical properties have been changed", if you are referring to anything I have not noted above. I imagine at some point, balsa core can be wet like it was when it was first sawn from the tree, and then dried again before serious degradation, but what would that point be? Likely this is the status of my third category above, but what do I know?

As to the weight of the epoxy... Unless I have botched my calculations
holes 1/4 inch diameter 5/8 deep on average centres of 1.25 inches for 30 square feet is an aggregate volume of about 85 square inches or 1.4 litres. No idea what the SG is of epoxy, but let's call it 10 pounds worth of epoxy to fill the holes. Let's say whatever inelegant way I fill the completely rotted areas adds another 40 pounds. Am I really to get excited about 50 pounds added to the deck of a 10,000 pound boat? Really? For a moderately old fart like me who just wants to go sailing and not have his core degrade in the future.

As to brittleness, this may be the most serious issue. It would be a bloody shame to have these areas crack and allow water in again. I believe this is the concern, please correct me if I am wrong. I have gone down the path I have gone down. I am all ears if you have any recommendations here other than epoxy/colloidal silica fills and the preferred solution of glassing the surface.

I suppose that once I have the holes all sealed and thus the rain sealed out, I could remove the tarp and have some freedom to work in comfort and safety. I could then choose to grind off the top 1/16 of an inch and glass the affected areas one area at a time between rainfalls and freezing nights in order to address the brittleness issue.

Cheers,

Boulter
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Old 16-05-2013, 23:32   #5
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Re: Wet core, CT-33 moisture meter, and me

Oh yes, glassing the holes is a must regardless of what you inject. That's why I said it will take longer than a seam. If you must inject, use a grease gun with tapped in zerk fittings to do it. Done properly, this will minimize the risk of voids. Inject something relatively flexible, definitely not epoxy with colloidal silica. I would suggest six 10 or poly core bond. None of these materials are intended to be used in such thickness however, and I suspect all will eventually crack due to deck flexing, unless the deck is unusually stiff or not used much. I've opened up a number of deck jobs that had been injected at some point in the past, it's usually a real eye opener to see just how far the filler made it. Don't inject resin, I've seen people do this and keep shooting in quart after quart, thinking they are filling a void, only to realize its coming out a hole in the inner skin and squirting all over the headliner and the inside of the boat! I would guess that balsa that reads above about 20 relative is too wet to recover, and will eventually dry rot even if successfully sealed. But who knows for sure? That's the whole point, it's a gamble if you start going that route. I chase back to clean blonde wood that reads less than 15 at the most. It's too much work not to do it right the first time. But that's easy for me to say, I get paid to do it. Good luck with whatever method you use! Sounds like its not huge at least...



http://www.westsystem.com/ss/new-six10-epoxy-adhesive/
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Old 21-05-2013, 06:59   #6
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Re: Wet core, CT-33 moisture meter, and me

Hi Minaret:

Thank you for the additional advice. I know for sure I am going to cut off the cockpit floor from the top as it is completely gone through and through. After I do that, I might find myself in a place to do the rest of it the same way.

Cheers
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