I am attempting to make curved corners instead of straight 90 degree corners for the wall-ceiling and wall-wall corners in my bathroom renovation. See attached simple scetch.
I've been using USG "Plus-3 Lightweight All Purpose Joint Compound" for taped joints and initial 90 degree corners with fine results. I like the Plus-3 because it sands well - its dust has less tendency to fly into the air and tends to drop right down.
I started 'curving' the corners using my homemade version of, what I initially thought was like, an adjustable Bull-nose trowel using the same USG Plus-3 mud. I've been building up layers bit by bit (I'm in no particular hurry) and feather out. As each layer dries and cracks a bit as with normal "first coats". I just sand a bit and/or sponge sand evening out as much as possible in-between layers. I've even thinned the mud and painted some on with a paint brush. I've added a bit of dish detergent to the mud to reduce the bubble holes and get more smoothness. This has all been working fine.
I've ordered an adjustable "Versa-Trowel Bull Trowel" from www.All-Wall.com
for corners I haven't started yet because I was thinking it would be easier in the long run for the price. It's supposed to be adjustable between 88 and 155 degrees. I'm waiting to see if it would help or not. I'm thinking it is really for corners where the drywall meets at odd angle due to off 90 angles like dormers, etc. Thus, it would still give "straight" corners - just not at 90 degrees - no curve though.
My paranoia began when another renovator (son-in-law) saw my interim job (with some cracks) and said there was too much mud and it would continue to crack. Now I'm worried about the long term ramifications; like cracking through paint or even the whole corner curve just falling off months or years down the road.
Surely there is a way (or technology) to sculpt curved corners or man wouldn't have landed on the moon. Something like an adobe architecture.
My questions are: Am I using the wrong technique, or the wrong mud (USG makes lots of different plasters), or the wrong tools? Possibly when starting other corners I should use vinyl inside corner beads? But, I want way more of a curved corner than I've seen in the vinyl inside corner beads.
I am now worried that I'm using the wrong kind of mud or plaster. Maybe I should have used a plaster that "sticks" much more over the long run? I've never used "Durabond" and don't know if it's more appropriate? Changing plasters would be okay except that I've done quite a bit with the "Plus-3 Lightweight".
I've been doing drywall and mudding on and off for a many years with total success. I also have experience with "life-casting" using silicon molds and hydrocal plaster. Hydrocal might be okay except that it sets up hard as a rock in something like 15 minutes. It's really made for casting in molds.