Form liners are available in a wide range of standard shapes, sizes and patterns, but sometimes these ready-made designs fall short of achieving exactly the effect an architect or builder or developer has in mind. In such a situation it makes sense to consider using a custom form liner made of either polystyrene foam or rigid elastomeric polyvinyl chloride. Choice of material for a custom form liner depends on the number of times the liner will be reused. If the design is for one-time use such as an address or company logo or small area, the most economical material is expanded polystyrene foam. This suitably rigid and extremely lightweight material can create almost any shape at costs below those of steel or wood construction methods.
Polystyrene form liners may be used for either tilt-up or cast-in-place construction. For an original design, the only additional cost is to create a master mold. Liner price is determined by the thickness of the liner, plus a nominal setup charge. Occasionally plans call for a trapezoidal rib form liner pattern that is not available in a standard size. A smoothly finished, non-porous polyvinyl chloride plastic liner (typically with 4 to 10 reuses) can be used vertically or horizontally in cast-in-place or precast construction. The major consideration in developing a custom pattern is the angle of the draft that is, slopes on the sides of the trapezoid because the durability of the pattern is based on the height and width of the trapezoid.
When a job calls for high reuse, the most reliable results are achieved with elastomeric form liners. The reverse image polyvinyl chloride (PVC) or urethane plastic sheets impart a wide variety of textures and patterns to poured concrete surfaces. No further treatment after pouring concrete is normally required to achieve the desired texture, thus saving finishing costs.