I, too, mix a little less hardner than an equal length. It doesn't lengthen the work time very much, but every bit is a help. I also tried scraping a little roll of the mixed putty onto the back edge of the Tamiya zimm tool and was able to spread and texture it at the same time. It worked well for me. One other thing you can try is using Bondo automotive putty hardner. It's red, but seems to give a little more work time.
Scraping through to the base plastic isn't really a problem. Once it's painted, you can't tell it's down that far. I had an easier time controlling my texturing by scraping all the way to the kit plastic.
Oh, one more thing...Don't over look the little scraping tool that is on end of the handle of one of the bigger tools. I did for a month or more, and it is really a handy little tool for those tight spaces areound the kebelblende and driver's ports.
I hope some of this helps.
Bill
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DML M4A2 Red Army
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-- There is a fine line between "hobby" and "mental illness". (Author unknown)