Well, watched it again... don't know why he would say that because the main function he uses it is to prevent embolic reaction on branches to accelerate healing and prevent die-back. What he says right after that is a complete contradiction on how Callusmate works, and its a completely oxymoron statement against their sale ad.
Waterproof will not let water (or air) in or out. By experience, this thing is the most waterproof sealant for bonsai in the market, Top Jin is very similar, but I prefer Callusmate.
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