Understanding Plyform Tolerances

This information is adapted from APA’s Concrete Forming Design/Construction Guide.

Tolerances help minimise the time and effort required in building forms.  Understanding what is possible makes it easier to solve problems that arise on-site. For example,  two sanded panels with a Performance Category of ¾, both within manufacturing tolerances, could form a joint with a 1/32″ (0.8mm) variation in surface level from panel to panel.  Realignment of panels and shimming becomes a quick and easy solution.

Tolerances & Squareness of Plyform
Requirements as laid down in US Voluntary Product Standard PS 1-09 (Section 5.10)
Panel size

+0.00 / -1/16″ (1.6mm)

Performance Category & Thickness

Sanded Plyform ≤ ¾” (19mm)

±1/64″ (0.4mm)

Sanded Plyform ≥ ¾” (19mm)

± 3%

Overlaid Plyform (HDO/MDO) ≤13/16″ (20mm)

±1/32″ (0.8mm)

Overlaid Plyform (HDO/MDO) ≥ 13/16″ (20mm)

±5%

Squareness 1/64″ (0.4mm) per nominal foot or 1.3mm per lineal metre of the longest edge – ±1/8″ (±3mm) difference in the diagonal measurement of an 8′ x 4′ (2440 x 1220mm) panel.
Straightness A straight line drawn from one corner to an adjacent corner shall fall within 1/16″ (1.6mm) of the panel edge.