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Discussion Starter · #1 ·
So, the backstory. My little E20 was in an altercation with the lightpost at the boat ramp wherein I smashed a small hole in the back of the cockpit coaming. On this boat it's part of the deck and sweeps down to the very stern. Upon cutting it open I found rotted coring. :mad: It crumbled in my hand as normal and I started cutting up the top of the coaming to expose the bad core for replacement.

Here's there my confusion comes in, I've cut about 30 inches up the coaming, the coring still looks wet (dark) but it's so solid I'm having to router it out off the inner skin. How do you decide you've reached 'good' core? I'd hate to recore the entire deck only to find out they used a darker plywood in the factory and it was fine the whole time.
 

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It's moisture you're trying to get rid of, along with any rotted core. Stuff that's still firmly in place, but damp, can sometimes be dried out without ripping it all out. Color can be an indicator, but it isn't always reliable. Like any wood, balsa can vary in color a bit. Drying out core takes a long time - the longer the better, generally. Hair dryers, vacuum cleaners, lightbulbs, heat lamps, fans...All are tools to consider using. People sometimes go at it for weeks. The water's been leaking into there for years, probably, and end-grain balsa is a really tight-grained sponge, not easy to dry out. Once the core is as dry as you can make it, still nicely attached to the substrate, you can take a shot at re-glassing it. We had leaks in our companionway hatch that infiltrated forward about five feet into the coachroof. Where the core was still solidly attached, we let it dry out as best we could and 'glassed it over. That was ten years ago now.
 

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If you have access to a 'chemistry lab' or know someone who works in one, the process is very easy:
1. take a 'fresh' sample, wrap it tightly in plastic wrap, and then put it all into a plastic bag and all of that into a small glass jar with a tight fitting lid.
2. Have the sample weighed on an 'analytical balance' to the nearest 1/1000th gram
3. Then have them put the sample into a desiccating chamber/jar until 'constant weight' is obtained, probably a week or two in a 'desiccant jar' ... the moisture will be drawn out and into the desiccant. Weigh the sample when its at constant weight (dry).
4. the difference between the weight obtained in #2 minus the weight in #3 can be assumed to be water.
5. if the amount of the difference is more than about 5-8%, then you can assume that wood has been saturated with excess moisture.

For a more practical approach
1. assume that there isnt much 'dark' plywood made on this planet
2. Make a small drilling (from the underside) into an area you suspect where there is NO wetness.
3. Compare the color differences .....
4. keep 'ripping' from the 'dark zone' until the color closely matches the lighter color removed from out of that dry 'undersurface'.
5. remove all 'wet wood'. Reason:wet 'darkened wood' or wood that has already changed color due to wetness usually is infected with fungus (mycelia) and these 'micro-tendrils' will continue to spread and force their way through the wetted wood and cause rot .... (dry rot) even if the wood is later dried out.

;-)
 

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Discussion Starter · #4 ·
I hadn't thought of drilling a test hole on the inside for a comparison. I'll give that a shot tomorrow then, thanks for the idea.
 
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