I purchased a J/30 last summer that I'm in the process of recoring and generally rebuilding. I'm impressed by the collaboration and generous community on the J/30 class site, so I thought I'd share some of my story with some point specifically regarding the vermiculite in the bilge issue.
My boat suffers from several big problems:
1) The core below the waterline on the starboard side is wet 3/4 of the way up to the waterline
2) The core on the port side is wet around the keel sump for about 2' surrounding the keel
3) The vermiculite under the floor was soaked with black mold and diesel
4) The foam under the ice box has hydrolyzed in spots and very moldy
5) The boat smelled nasty
Sounds pretty grim, but my repairs are going nicely and I expect the boat to be beautiful, strong and in the water this June. I'm taking steps to do a pretty radical renovation, but in the end it will save time on my repairs (no pussyfooting around, or tactical use of self-delusion) and make the boat easier to maintain and inspect in the future. In any case, I thought I would share my findings under the floor since their is some question about what's going on in there.
I am doing much of my recoring from the inside since it will minimize the amount of fairing that I'll have to do on the completed hull and because I had to eradicate the 'rotten old boat smell' coming out of the floor of this boat. To accomplish this, I have cut the old floor out and stripped out the vermiculite under it. The floor itself was teak and holly on top of a 3/8 cored fiberglass laminate floor. While my T&H was beautiful, the floor/vermiculite under it was a nightmare.
When these boats were manufactured, the molded interior was bonded to the hull using either vermiculite or shredded chop strand, either of which were basically mixed with polyester resin to form a bondable 'peanut butter'. Several areas are bonded with chop strand for strength and durability - under the mast step, under the engine, under the vertical side of the quarterberth units. This material does not absorb water and is bulletproof. Vermiculite was used generously elsewhere, especially under the floor, which is basically solid vermiculite between the roving of the hull and the floor laminate. The vermiculite sends my Aquant water meter right into the red, its soggy and in spots, brittle. I chipped it out pretty quickly with a pneumatic impact hammer.
As you know the bilge pump hose was laid permanently in this vermiculite down the center seam of the boat. About 3 ft back from the keel sump there is a low point where water collects in the solid glass center seam. Unfortunately, as soon as this hose breaks down, pumping out has the effect of pumping water into the vermiculite. In my boat, it also appears that diesel had collected in this area, probably as a result of a spill during a filter change. When I opened up this area, it was ugly - full of black mold and a greasy wet collection of water and vermiculite... Yikes.
The previous owner had obviously figured out that the pump hose was leaking and had threaded a smaller diameter reinforced hose through the old hose and into the bilge (which I see was suggested in this forum previously). This seems like a reasonable approach to this problem, though it doesn't mean that water won't migrate forward from the cockpit/companionway area and collect behind the bilge. Also bear in mind that when you heel that yucky water will migrate around the bilge, either from the bilge into the vermiculite or vice versa.
If you don't want to get radical with this repair, I would consider putting in an inspection port on this wet spot, so that it can be kept dry. Finding the low spot is the trick - I would look at the hull from the outside and identify the low spot as measured back from the trailing edge of the keel. The center seam is a consistent thickness (until you get right up to the sump, where its reinforced), so the low spot outside is the low spot inside. I have decided to put the floor down in such a way that I can open it along the center seam for cleaning and sponging (if necessary). I might also see if I can add laminate to this seam to give it a pitch that will allow it to drain. The way it was originally designed, this area simply can't be dried, short of standing the boat on its nose for a while. Later J's corrected this issue by ensuring that the bilge could drain continuously from both ends.
As an aside:
All early J's are very susceptible to wet core issues. If you do have substantial moisture, it will collect adjacent to the center seam since the water migrates downward. Plus, the core goes right up to the keel sump, so your weakest wettest core is right over the most stressed region of your hull. On my boat, the core around the sump was similar to the nasty sponge sitting on the edge of your kitchen sink (not kidding). That having been said, these boats are VERY heavily built with at least 1/2 inch of roving around the keel sump over the core. I suspect that there are many wet boats out there that have not had issues because this inner laminate is so strong and the keel sump is very rigidly built. My boat had no deformation or sign of stress related failure, but as a bit of a perfectionist (and former glass and rigging man at a shipyard), I figured I'd make this boat right while I was 'pimping' it out. If you do decide to do a recoring, considering doing parts of it from the inside. Doing it from the outside is much harder because you have to completely re-fair and unless you've got the boat upside-down, gravity is working against you. I am only recoring from the outside in places that can't be accessed from the inside. Bear in mind, these are structural repairs, so make sure you have a broad bonding margin between old and new. Also use epoxy and not poly or vinylester resin since non-epoxy resins do not bond well to cured or dissimilar materials.
Finally, if you don't have barrier coat on your boat, you're crazy. My boat got soaked from simple blisters. The outer laminate on these hulls is unbelievably thin (less than 1/8), so if you have a blister, its very unlikely that its just 'in the glass'. The previous owner had shoddy repair work done with generous use of inferior filler material that ensured that the problem just got worse and worse each year. If you do have some moisture, at a minimum repair the blisters with epoxy and colloidal silica (not polyester filler or marinetex!) and apply a barrier coat like Interprotect 2000 (goes on better than anything else I've used). If you can risk the sleepless nights, get one of these: http://www.gesensing.com/products/aquant.htm?bc=bc_ge_protimeter
I'm looking forward to racing and cruising my J/30. A few people have asked me why I bought an old J/30 - I ask them to show me any ~30ft boat with superior speed and cruising amenities. You can name lots of boats with one or the other, but none with both.