Tools and Materials
You don't need specialized equipment for swirl texture. Here's what I use:
Joint compound: Pre-mixed all-purpose compound works well. Avoid lightweight compound for texture work as it can be too airy and doesn't hold crisp pattern edges as well. A 4.5-gallon box costs around $18 to $22 and is more than enough for a standard bedroom.
Brush: A 4-inch chip brush from the paint section is my standard choice for tighter swirl patterns. A 6-inch brush gives slightly larger arcs. Some people use a cellulose sponge, which gives a looser, more irregular pattern. For matching, try to identify what was used originally by examining the texture closely under raking light.
Mud pan or bucket: You'll be loading your brush repeatedly, so a wide container is easier than reaching into a compound bucket.
Primer: If you're texturing a repair patch, prime the patch first. Raw compound and raw drywall paper absorb moisture from fresh compound differently, which affects drying time and can show up as texture inconsistency after painting.
Mixing the Compound
Texture compound needs to be thinner than standard taping consistency. If you put the brush in and drag it across the wall, you want the compound to move smoothly and leave a clean defined edge, not tear or drag dry.
Start with your pre-mixed compound and add water a tablespoon at a time, mixing thoroughly between additions. You're aiming for the consistency of smooth peanut butter, thin enough to spread easily but thick enough to hold the brush marks after application. If it's so thin that the marks start to settle and blur before you finish a section, add more compound to firm it back up.
A quick test: load your brush and make a swirl motion on a scrap piece of drywall or cardboard. The pattern should stay defined and not slump. If it slumps, the mix is too thin.
Applying the Texture
Load the brush with compound but don't overload it. You want the bristles coated, not dripping. Excess compound will blob at the start of each stroke and create an uneven surface.
Work in small sections, roughly 4 to 6 square feet at a time. Apply a thin, even base coat of compound first with a drywall knife or roller, then immediately work back over the wet surface with your brush to create the swirl pattern.
For the swirl motion, use overlapping arcs. The classic technique is to start at the bottom of your section and swing the brush in a half-circle or quarter-circle arc, then overlap the next arc by about a third of the brush width. Some people use a consistent clockwise rotation; others alternate directions to get a more random look. Either works. What kills the result is being too systematic and creating a grid pattern that's obviously regular.
Keep your pressure consistent. Too light and the brush skips. Too heavy and you scrape through the compound down to the wall. A medium, even pressure that lets the brush glide is what you're after.
Ceiling vs Wall Application
Applying swirl texture on ceilings is harder because you're working overhead and the compound has a stronger tendency to drip. Use a slightly thicker mix than you would on walls, and work faster. Gravity will pull the wet compound down, which rounds off the swirl edges over time. Getting crisp ceiling texture means working in small sections and finishing the pattern before the compound starts to sag.
Matching Existing Swirl Texture
Matching is the tricky part. The existing texture in a room was applied by one person in one session, and their brush size, arc diameter, and compound consistency are baked into every wall surface. Your job is to reverse-engineer it.
Before touching the actual wall, spend 20 minutes testing on cardboard. Try different brush sizes, different arc diameters, and different compound thicknesses until you get something that looks close when held up next to the existing wall. It's worth taking the time. A patch that's 90% of the way there in terms of matching will be obvious after painting. Getting to 95% or better requires that calibration work upfront.
Under raking light (a flashlight held at a low angle to the wall), look at the existing pattern. Note the arc size, whether the individual brush marks are tight or loose, how much overlap there is, and whether the pattern is directionally consistent or random. Then try to replicate those specific characteristics on your test cardboard.
One common issue: the existing texture is old and has been painted over multiple times. Paint fills in fine detail and softens edges. Your fresh texture will look crisper than the original until it gets painted, at which point it should match better. Factor that in when evaluating your test patches.
Drying and Finishing
Let the texture dry completely before painting. In normal indoor conditions, swirl texture applied at reasonable thickness should be dry in 24 hours. Thicker applications can take longer. The texture should feel completely dry to the touch with no cool spots before you prime.
Prime with a drywall primer before your finish coat. Applying paint directly to fresh texture without primer causes uneven absorption and a blotchy finish. I use a thick-nap roller (3/4 inch) for textures to get paint into the low spots without flattening the peaks.
The USG installation guide and various manufacturer resources cover compound mixing ratios if you want specific numbers. For swirl texture in particular, the general guidance from finishing professionals is to err on the side of slightly thicker compound rather than thinner, since you can always thin more but can't easily thicken once it's on the wall and starting to set.