Q.: We like the look you can get with textured plastic form liners, but we always seem to have trouble fitting them together or matching up ribs when we place a second lift. How can we do a better job?
A.:You're not alone with this problem. In general, butt joints between either horizontal or vertical liners should be avoided because it's difficult and time-consuming to match liners so they appear continuous. Some ribbed liners are made with interlocking flanges, but this helps with joints in one direction only. Some of the elastomeric (rubbery) liners that have to be tightly and accurately mounted on form panels are flexible enough to permit satisfactory butting. This helps, but only within the area covered by a single panel.
The best solution, which frequently involves the cooperation or consent of the architect, is to use a rustication strip or groove former to accentuate rather than hide the joint. The rustication strip should also be used at all cold joints in architectural concrete (see photo). Certain liners having random patterns cannot be matched either horizontally or vertically. A rustication strip is always advised at joints in such patterns.
If butt joints are unavoidable, be sure to prevent grout leakage with compressible foam tape, caulking, or other material suitable for the particular liner. For liners with a strong vertical pattern, make the joints along the main features of the liner. Position the joints so they fall in recessed or shadow areas of the concrete where they are less conspicuous.