Foilholio, thanks for your reply. Your breakdowns of solids contents and coverage rates made my brain hurt the first 3 or 4 times I read them but I think I'm onto it now...
I actually had no idea you went down the Shoo Goo path, I thought you were a die hard silicon man! How is the kite looking? I found that my Shoo Goo coated test pieces did ever so slightly yellow over a number of weeks in the sun, and the porosity ratings also progressively got a little worse over time.
The silicon used in my tests was acetic cure as I had read on the forums (maybe by yourself) that it was significantly stronger and better adhering than the neutral cure.
To be honest, I'm not sure how many tubes of Marine Goop I used on my actual kite, I think probably 1 and a bit (it was the 10.2oz cartridge though, not the 3.7oz tube). I had some solution left over as I mixed up more than I needed due to my actual coverage being more on the kite than the rate that I had projected from the test pieces. I did however go though quite a bit of my imported stash for all the initial testing, probably close to 2.5 cartridges. However, the numbers you have come up seem pretty close from memory. I'd say on an actual kite, the second coat would not add the same weight as the first, maybe somewhere in the vicinity of 75% would be closer due to the fact the fabric is already pretty well sealed. Again, we have to very careful with the weights listed against the samples, they are significantly heavier than in actual use (at least on my S3s deluxe fabric).
In regards to your question about the Xylene version, it is a Canadian formulation, probably not available in the USA. The PDS and MSDS is available from the Eclectic Products website. Canada has restrictions on Toluene so this is why they went this route and as I am led to believe, the actual cured product is identical. Like I said though, Xylene evaporates slower than Toluene so that works for me with a longer working time, see attached publication on the relative evaporation rates for solvents relative to Butyl Acetate.
Your second question was about seepage. What I am talking about here is the amount of light that the test piece let through when looking though it at a light source. You can tell a test piece will have a good porosity reading just by observing that the light is diffused evenly throughout. If there are any 'light pinpricks' showing through (seepage) it obviously indicated that that fabric weave has not been successfully filled. Kinda hard to explain in words, Koala Products do a much better job in their #25 application instructions than I have.
Finally, in my opinion you need at least 15 to 20 before and after tests on the various parts of a kite to get conclusive results on the effectiveness. Obviously the kind of porosity testing that I did will not tell you the amount of leakage you are getting through the seams or whether it has been improved by coating, this is something that only a internal pressure test like you describe may assist with, but a quick and dirty test is how long it stays inflated on the beach after landing (laid flat). On a similar note, there was also some discussion about the different colours of fabric's porosity degrading at different rates, I think my testing found some evidence of this but nothing conclusive as the sample size was too low.
Cheers,
Axel