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Originally posted by Phil:
I have an older J-30 with the same moisture issue you describe on the starboard side of the hull.

Postings other places on this site indicate that the primary source of this moisture is from the engine exhaust.

I have had the area around the exhaust tube rebuilt and also have had the worst area of my hull where delaimation had begun (starboard stern quarter) re-cored.

Two questions:

1) What areas of mosture intrusion into the core did you identify, if any, other than the vermiculite/bilge line ?

2) Since I am not re-coring the entire starboard side of the hull would barrier coating be of any value? Since there is moisture in the core, isn't it almost certain to get into the laminate even if I barrier coat?




Unless your bilge is full of standing water, I'd say the overwhelming likelihood is that your core is wet from the outsite. This can be from blisters, damage to the outer laminate or a crappy thru-hull fitting. My engine's water intake (starboard) is bad and wet in the immediate vicinity. The rest of the core in that area is OK since there's no blistering.

The vermiculite is a great destination for water, but doesn't seem to impact the core it is next to. The inner laminate is several times thicker than the outer laminate, so its less susceptible to osmosis that penetrates the core. Not impossible that your water is coming from the inside, but it seems to me less likely.

The standing water aft of the bilge seems to collect on the center seam, which is solid glass, so, again I think the core is less likely to be impacted from the inside than the outside.

Finally, to reiterate: if you don't have a nice thick barrier coat, you're taking an unreasonable risk in *all circumstances*. A barrier coat slows or halts existing problems from worsening and keeps new problems from cropping up. Blistering gets more likely under three conditions:
- Warmer water
- Lower salinity
- Freezing weather in winter

So if you've got a boat up in Maine, you're likelyhood of blistering is mitigated (but still a substantial risk) since the penetration is slower. If you've got it in a freshwater lake in Texas, you're in prime osmosis territory. The other factors is the presence of freezing air while the boat is being stored. If you've got osmosis in your hull, but it never freezes when you're boat is on jack stands, your water may evaporate out without actually busting the surface (though it will still weaken the gel and laminate). If your soggy hull goes through a series of freezes in the winter, you've got a perfect set of conditions for expanding water to crack your gelcoat and develop classic blisters. Over time blisters always get worse if they are not fixed. If you have a substantially wet core, a barrier coat will slow the problem, but its not a fix by any stretch of the imagination.

Finally, one interesting thing to note. Since fresh water makes blisters *more* likely, special attention should be paid to 'Fresh water boats' on the market. This is great for some corrosion issues, but can actually be a check in the negative column as far as wet core issues go.


Rich Miller
Brass Monkey
#294