The house I'm working on is very old. Could that be the reason for air bubbles going over plaster? How do I get rid of them?
It's difficult to say what you may be doing wrong without actually watching you. You may be over aerating the mix; keep the paddle speed at moderate to low & use a circular motion, around the tub, rather than up & down as this tends to draw in more air. The mix may be slightly too thick & this tends to trap air & makes it more difficult to dispel as you float on the first coat; it also makes it over thick! Your trowel action (both angle & speed) could also be a contributory factor. You've obviously mastered the basics; try practicing different techniques on a gash bit of board (or wall & scrape it off before it sets) to see how you can improve your technique.
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