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

The patch that I dug out a few days ago has now been back filled with some Divincell foam core that I snitched from my brothers boat plant. Piecing the bits together was a pain, but that stuff is expensive. While I might like to do all of my core work with this kind of product that would be extremely expensive. Doing this work with balsa will be expensive enough I think. What I guess I will have to rely on is that the epoxy resins are far more impervious to water, so the blistering problem that caused the balsa core to fail should be eliminated. So I will have to compromise some on this part of the project.

Today my new pneumatic impact hammer arrived and in fairly short order I was able to remove the skin from an area about 2' x 3". This tool was very easy to use and is much easier on the hands then using the pry bars and a hammer like I had done before. It would have also been the perfect tool for removing the vermiculite when I was doing that project last fall. The chisel has a fairly rounded edge and does not want to dig in, unless you want it to. It separates the skin from the core easily and quickly and doesn't make much of a mess. While I have a large compressor in my shop I think for skin removal a small portable compressor would work just fine to operate this tool with.

Now for the interesting part of this adventure. Prior to pulling the skin off in this area I had mostly dry readings after using the vacuum drying process. Once the skin was off the entire area showed as wet core (again). Someone that is more technically inclined might be able to explain that one to me, these meters are supposed to indicate core as well as the skin. WIth the skin off you can easily see the areas of the core that absolutely need to be replaced. These areas are not black or gooey, just in very softened state and are about 15% of the total area exposed. With the skin off I think you could use the vacuum drying process even more effectively, but with so much area needing to be replaced I think the time spent to just completely replace the core would make more sense. I have some ideas about how to use a small plunge router to remove these bad patches, but doing larger sections of core all at one time is just going to be easier to accomplish. I pieced together the port side with the foam and that was more work than it needed to be. Larger sheets will just make this go faster.

On the port side I used my high volume vacuum pump to pull the foam into the hull. This pump can only barely pull about 5 inches of Hg., but it can do that all day long without heating up and it is relatively quiet. I think you can get the same effect with a shop vac, but I'm not so sure how they last when running for extended periods without air to help cool the motors. The other thing that is cool about this setup is using an inexpensive sink drain as the vacuum port. I just ran the 3/4" pvc hose into the drain pipe and taped it off.