Acrylic craft sprays generally come in two forms: a clear sealant for use over painted finishes or a water-based paint. The sealant can remain sticky until it fully cures, which takes two hours. All sprays, paints and sealants are affected by environmental conditions such as heat and humidity, so drying and curing times will vary based on the conditions in which you work with them. If, after four hours, an acrylic craft spray remains sticky, you probably have a defective batch and should return or exchange it. There are several things you can do to diminish the stickiness of acrylic sprays.
Mask areas you do not want to be hit with overspray when you use acrylic spray paints. This will not reduce stickiness on what you have sprayed, but will isolate the paint only to those areas you want them on. Lay crafts on plenty of newsprint or paper towels to handle overspray when you use acrylic spray sealants.
Wait until the paint on the craft is fully dry. You should never spray an acrylic sealant onto a painted craft until the paint is completely dry. Otherwise, the sealant could react with the paint and fail to cure properly.
Know the proper curing time. Acrylic sealant sprays often feel dry to the touch after 15 minutes, but do not fully cure for two hours. If you start handling the piece extensively just because it feels dry, you can interrupt the curing process and cause it to remain sticky longer as it interacts with the warmth, oils and moisture of your hands.
Use a room dehumidifier if you normally work in an unusually warm or damp room. Warmth and humidity can cause acrylic craft sprays to take longer to cure. If you dehumidify the air you work in, the sprays will cure much more quickly. Even so, allow pieces to cure a full two hours before handling them.
Be careful when exposing the craft to moisture. Acrylic spray paints, as opposed to sealants, are sometimes used because they are water-based and can be cleaned up with simple water before they fully cure. After curing, they become water resistant and require paint remover solvents to be cleaned up from spots they should not be. If you use a damp cloth to remove overspray, take care not to get any of the moisture on the surfaces you wanted painted, for this will increase the curing time -- and leave the paint tacky and sticky for longer than normal. The acrylic spray sealants are much the same and should be handled similarly, though overspray with sealant will not discolor the pieces it touches, so it does not need to be dabbed off for aesthetic purposes.
Acrylic sprays are prepared at a particular consistency. A defective batch might have too much thinner in the mix. This will not stop the acrylic spray from drying, but will extend the curing period and leave it sticky for longer. You can usually solve the problem by leaving the piece to dry overnight while exchanging the defective spray for a new can.