Achieving a high-quality finish in an architectural concrete formliner project begins before any concrete is poured. By properly setting up forms, ties and lining up formliner joints beforehand, your project will be prepped to make finishing and staining the project an efficient process.
When preparing forms for architectural concrete they need to be aligned and set in common planes otherwise a “stack-up”- a noticeable “step” in the finished surface – of manufacturing tolerances may occur in forms being on different planes. This is especially crucial when working with shallow formliner patterns.
In order to ensure that formwork is sufficiently rigid and will remain sealed during concrete placement and vibration, all joints and tie holes should be sealed by caulking or the use of gaskets to prevent grout leakage. Do not “lap” formwork over previous pours that have uneven architectural surfaces. Such lapping will result in a form offset with leakage that distorts the finished concrete appearance. For further recommendations please consult ACI 347‐01.
To minimize the visual effect in the finished surface, plan formwork so tie placement is at rustications, reveals, or other inconspicuous locations. Remember to allow for the depth of the formliner when calculating the breakback requirement for ties.
When using a rib pattern formliner, locate ties at the high point of the formliner rib. This places the tie in the recess of the finished surface where it is less noticeable. The maximum diameter of the tie (cone, She‐Bolt, Taper Tie) should not exceed the minimum width of the rib.
Provide a minimum of 1″ concrete cover for ties requiring breakback.
If cones are used, the diameter of the cone should be less than its depth to facilitate patching.
It is very difficult to match pattern features at joints and ensure the surface appears continuous. Slight differences in shape, thickness, and texture will have a visible impact on the finished surface. For this reason, avoid or minimize both vertical and horizontal joints. Patching, sacking, grinding, and coloration – when done properly – provide an excellent way to greatly minimize any seams or joints.
When joints are unavoidable, make the joint along the main features of the pattern. Match pattern features carefully, and minimize grout leakage at the joint with caulking or foam tape. This practice will help reduce the visible effect on the finished surface.
Consider the pattern dimensions to achieve an overall balanced design. It is especially important to consider pattern dimensions when planning for unavoidable joints, boxouts and corners in the finished surface.
With a little advanced preparation your completed architectural concrete project will be set for a timesaving, easy finish.