I've heard that wax paper can foul an epoxy before. But in my experience its never been a problem and is infact, my preferred surface to mix a small dab of epoxy up. Most of the time I use small coffee stirrers (plastic straws) to mix with. For a larger batch such as when fuel proofing a firewall or tank compartment I use left over plastic pudding/yogurt cups and popcicle sticks.

Whenever I've had a "soft pour" where the epoxy either doesn't cure or comes out "rubbery" I now believe its the result of too much hardener. When I use a flat surface like a paper plate or piece of wax paper I make a small puddle of resin and then right next to it I make a small puddle of hardener. Then mix together thoroughly folding it over, scraping together, and stirring well. Practice a few times and when uncertain use just a tad less hardener than resin.

Its difficult to believe when I've used graduated measuring cups I've had the worst luck. Just eyeballing small puddles has been the most reliable. I also prefer 30 minute and 15 minute epoxy and use nothing faster now. I've had just as good results with Tower Hobbies brand as I have name brands but I only use those sold in hobby shops and not the hardware store stuff and I just flat out avoid the stuff packaged in double-barrel syringes.

I'm much more confident than I used to be yet always have a feeling of relief when an epoxy takes a good set. And when I'm going to hang an engine of 1hp or more on it and me stand in front of it to start it up I want a good epoxied firewall keeping that prop in check.

Practice with small batches and see if you don't start to feel better about it.

Regards,

Clay