When caulking, what can help sealants adhere to substrates before the sealant cures? Again, The Ins and Outs of Caulking has the answers for homeowners, telling them that tooling assures uniform sealant contact with each of the substrates and works air bubbles from the sealant. Tooling usually results in a more aesthetically pleasing joint as well. What tools?
As the photo shows, homeowners have some sophisticated choices for tools: fingers. Big box stores sell caulking tools, although a plastic spoon is usually satisfactory.
Emulsion acrylic sealants are the easiest to tool. Water is usually used as a tooling liquid (lubricant), and excessive adhesion to the wetted tooling device is rarely a problem. Polyurethane sealants often adhere mightily to tooling devices and thus usually require a lubricant on the tooling device. Some manufacturers of polyurethane sealants allow water or soap solution for tooling; others prescribe proprietary tooling lubricants. Silicone sealant manufacturers usually recommend dry tooling, although some may recommend a tooling lubricant. With some sealants, a tooling lubricant requires that the joint be completely filled prior to tooling.
Lubricant on the surface of just-tooled sealant or on substrate surfaces may interfere with sealant cohesion or adhesion, respectively, if additional sealant is placed in the joint. Because latex acrylic sealants use water as both a suspension agent and a tooling lubricant, they are relatively immune to this problem. Experienced professional tradespersons rarely try to tool underfilled joints.
In contrast, relatively inexperienced homeowners can reasonably be expected to sometimes make (and have to correct for) this error. The purpose of tooling is to improve adhesion between the sealant and the sides of the joint. Tooling will coincidentally push sealant back into the joint. One of the functions of backing material is to prevent excessive depth of sealant in tooled joints.