Moreover, as humidity and temperatures change, building materials also will expand or contract. Selecting the proper caulk will help ensure that the seal holds through shifting conditions. It must stretch and recover its original shape when the materials expand and contract. It must remain flexible as it ages. By itself, caulk generally is effective in gaps up to about a quarter-inch wide.
Some newer caulks can bridge gaps up to a half-inch effectively.
The depth of a crack or seam counts, too. Also, consider the temperature at the time caulk is applied. For example, if you apply caulk in the middle of summer, the substrate is fully expanded. If the caulk had been applied when the temperature was moderate and the substrate was between its fully contracted and expanded states however, the caulk wouldn't have to flex as far to keep up with the seasonal movement. Some surfaces create more adhesion problems than others.