J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Drying Balsa Core with Vacuum and Heat

So this lovely spring morning here in Oregon I was out chopping soggy balsa out of the bottom of my boat. After working this area for a couple of days with the heat and vacuum, what I managed to accomplish was to get the balsa to a damp condition. You can actually feel that the balsa is damp to the touch, but it is not black or gooey, just damp and very soft in some patchy areas. After removing this stuff I then got the 4" disc sander out and cleaned the inner skin up back to bare fiberglass. I think I knew this answer before I did this, but I got the moisture meter out to check this bare inner skin and it shows to be wet too. That doesn't actually surprise me, but it does make me think about what I have to do before any rebuilding steps. And all of this gets me to wondering what it is I am trying to accomplish here.

The reason to do this kind of crazy work is to get the hull back to its original structural integrity and back to a fighting weight. But there are lots of ways to gain strength without removing this balsa. The easy way is to simply add new layers of glass and make the outer skin become more structural, but this would add some additional weight. This wet balsa is structurally compromised as compared to its new dry condition, but even damp it is still providing some significant structural strength, so if you just add more glass for strength, how much would you add?

What I am getting at is that it may be good enough to suck the juice out of this thing, leave the existing balsa in place and then do a heavy glass with epoxy resin on the outer skin. The epoxy layer would seal the old skin from gaining any new moisture and likely greatly slow down the degradation of the old balsa likely by many years.

This boat has had some serious work done in the past too. Close to the keel the material I thought was wood is actually foam core and I don't think that is original to the boat. So at some point in time they reworked the area alongside and behind the keel and replaced the balsa with foam core.

One of the other interesting things to note is that the area around the old blister repairs must have been saturated with a penetrating resin of some sort. while the obvious part of these repairs is about the size of a quarter, the area that has been hardened up is much larger, several inches in fact. If this was the "nailing" technique then that is a more structural repair than I had been thinking it would be. Trying to remove the balsa around these old repairs would have be done in some other way besides just prying it off like the rest of the balsa, either by oscillating saw or grinder.

Anyway, I'm not trying to cheese out on my project, but I do want to go sailing someday too. So let me know what you think would make sense to do here, you all have way more experience with these balsa core boats than I do.

As an example after seeing the effect of those blister repairs I think one repair option would be to 1) continue drying the hull as best as possible 2) remove the outer skin to inspect the balsa. 3) use a penetrating epoxy on the exposed core. 4) Glass the exterior skin and fair. 5) Go sailing.

While I am waiting for all of your opinions, I think I will go out and saturate some of the exposed partially wet core with CPE and when cured test that area with the moisture meter. If the balsa becomes firm from the epoxy, then I would expect the meter to want to think that core is dry. For sure if it becomes firm then in my humble opinion that is good enough.