What tool to use for applying textured ceiling?
Yes a wallpaper glue brush is good but there are many types Ive used depending on the texture. I've used car washing brush(very soft bristle), straw wisk broom (stiff bristle), hand brooms, paint brushes, even a broken in half push broom. Cedar shingles and other stiff board type things work as well. Ive stapled carpet onto wood to make a trowel like tool. Scarify the edge of a rubber grout trowel. I even borrowed from the faux painters the "rag roll" by wrapping a rag over a paint roller. What ever tool used it is good to clean it very often to expose the bristle or what ever, so it remains consistent. Build up of mud on the tool will take you from detailed pattern to smearing in no time. Wipe the brush on a mud pan, hawk, bucket edge, what ever often. You may have to clean it with a sponge or other blade tool. Matching is always tough so as other writers advised, do use a practice area first. It wont hurt to mount your practice board overhead to get a feel for working on a ceiling.