Prism99

Here's what I recommend.

Lay down a large flat sheet first to catch any overspray. (Afterwards the sheet can be tossed in the laundry.) Tape the sheet to the floor, if you like.

Smooth out the batting on the sheet. (It helps to fold and mark the center of each edge before you do this.) Center the backing on top of the batting. (If you have folded and marked the centers of the backing first, matching them to the batting markings makes this really easy.) Fold back half of the backing on top of itself, exposing half of the batting. Spray the wrong side half of the backing, or the batting. (Spraying fabric requires less basting spray than spraying batting, and you want to keep the amount of spray you use as minimal as possible and still get good contact. You don't want to get any basting spray on the right sides of the fabrics, though, so sometimes spraying the batting is easier.) To minimize overspray, spray from the edge of the quilt towards the center. You want the spray to cover the entire area, but thinly. Fold the sprayed backing half over the batting, smoothing and repositioning as necessary so everything is flat. (It's nice to use a yardstick to smooth from center to edges, although not necessary.) Fold the remaining backing fabric over itself and repeat the process.

Flip the batting/backing sandwich over so that backing side is against the sheet and "naked" batting side is exposed. Mark and center the top over the batting. Fold back half the top and repeat the spray/smoothing process.

It's really important when spray basting to do it in halves as described above, especially with large quilts. The first time I used basting spray I sprayed the entire batting and then tried to position it on top of the backing. Was ultimately successful, but had a sticky mess on my hands and quite a struggle before I got it right. Works *much* better to center and position first, before spraying!