How to convert 90%v/v Everclear grain alcohol in to 42.8%v/v strength Alcohol ? ?!
Cut it with water. That's how they make all vodkas. They start with everclear and cut it with water until they have the requisite % alcohol.
100 proof vodka is basically 50/50 everclear/water. 42% just add a little more water. Won't be exact, but whatever!
Home brewer, cordial maker, uses everclear
210% more water than everclear, as 90 is 210% the amount of 42.8
math skills :=)
add exact same amount of water...it should bring that to at least 45 %