I am new to the remodel scene, and have been learning alot as I go. I had no problem taking off all the popcorn from the ceiling in my whole house. Then, I discovered that the joints of the ceiling in my basement had only a layer or two of joint compound on top of the tape before they applied the popcorn, thus when I removed the popcorn, many times it cut right down to the tape. That being the case, I had to retape many of the joints. Most of the joints were not a problem, but I have 2 joints that have just been nothing but problems. I went and bought the ultra thin mesh tape as I've heard that is the best to work with to prevent bubbles and such. I applied it. No problems. No bubbles. Applied another layer. No problems, no bubbles. Went for a whole 3 or 4 feathered layers (can't remember for sure) and there were no problems whatsoever. The whole ceiling was smooth. No lines or anything could be scene. All my other ceilings in the basement, I had been putting a final layer on of "topping compound" over the whole ceiling, to tame the roughed up fibers of the bare drywall, and such. So, I applied the thin layer of the topping compound to the ceiling in this room. Went in the next day, and what had happened? There was the long line of a bubble in the mesh!!! How am I suppose to avoid this? How am I suppose to fix this? Even if I rip it all out and start over again, how do I avoid it happening all over again since there was no problem until the last, 5th layer? What am I doing wrong? Any help, please?!?!?