I have no personal experience with such hulls but I know a fair bit about epoxy plastics and low viscosity plastics in general so I'll contribute what I can.
Firstly you need to look at the type of epoxy you are using. There are multiple different types which are differentiated by their viscosity and setting time (in particular for the application you are talking about). Other than that, there isn't much to tell apart one epoxy from another -- a low viscosity epoxy sold as a wood sealant and a low viscosity epoxy sold as a rust treatment are pretty much the same thing and will do each others' jobs, more or less. For what you are trying to achieve, which is to impregnate balsa, you need a low viscosity epoxy with a medium to long setting time.
I would say that even with a low viscosity epoxy you are going to have a lot of trouble completely impregnating balsa -- that is getting the epoxy to soak right through to the core of the balsa (no pun intended). Balsa is actually a hardwood, and the porosity of balsa is "vuggy" which means that the wood itself (once dried) is full of small self-contained (not-interconnected) pores or tubes, unlike a softwood where the pores are all interconnected. That means that there will be internal pores in the balsa that are not connected to the surface pores. The net effect of that will be that the liquid epoxy will not be able to flow directly via capillary action into the core of the balsa unless something mechanical is done during the impregnation process (perhaps pressure, heat or something chemical to break open the pores).
To cut the scientific talk:
* You can't impregnate balsa all the way through.
* If you don't impregnate balsa all of the way through you can't eliminate the chance of core failure -- the non-impregnated core may still fail.
* Water ingress can still happen to the internal non-impregnated core of the balsa.
* Most water intrusion into balsa cored hulls happens via holes in the hull -- either incorrectly installed through-hulls, screw holes, or simply just cracks created by impacts or stress of some kind.
* If you've got an incorrectly installed through hull that's causing water ingress it's still going to cause water ingress to the core of the balsa that might not be impregnated in epoxy.
* If you've got a surface crack then impregnating the balsa (at least to some thickness below the surface) should, in theory, stop any water ingress.
Does it reduce the risk of water intrusion? Yes, probably. Does it greatly reduce it? Good question, one that I can't really answer and you'd probably need to survey a lot of boat owners with and without epoxy impregnation of the core to get an answer.
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