By the way, on Epoxy, there are some rules you need to follow.
1) Clean and prep the area. When you think it's perfect, do it again.
2) Stir the epoxy with a smooth metal object. NEVER use a "stir stick". I've seen so many people use those wooden popsicle sticks, and they ALWAYS get bubbles. Why? Because the epoxy is heating up, and as that wooden stick (with all its pores) gets swished around in the mix, it releases little bubbles into it. Tons of them. Use a metal stick - think "nail".
3) The face of the transducer as well as the prepped area need to be completely covered with epoxy. Remember - Wet to Wet. Never put a wet epoxy covered item onto a completely dry item. Wet them both. When you put the wetted areas together, it results in much fewer incidences of bubbles.
4) Sufficient pressure must be kept on the transducer while letting it dry. Allowing it to just barely come up at any stage during the curing process WILL allow air bubbles to form - almost guaranteed. Have your "weight" ready so that the minute the surfaces are pressed together, the weight goes on and stays there until it's completely cured.
All the best,
Glenn