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 Understanding Plyform Tolerances

Understanding allowable tolerances makes it easier to solve problems that arise on-site. Start with the official Performance Category set down by US standard PS1-19 and the manufacturer’s recommended thickness, both given on the trademarked panel. These already take into account permissible tolerances.

For example – two different sanded plywood panels with a Performance Category of ¾ in, but both within manufacturing tolerances, can form a joint with a 1/32″ (0.8mm) variation in surface level between the  panels. Realignment and shimming is then quick and easy. Also check out APA’s complete Concrete Forming Design/Construction Guide.

PS 1-19 sets down tolerances & squareness for Plyform panel between +0.00 / -1/16″ (1.6mm).  See examples for:

  • Sanded Plyform : ¾” (19mm): ±1/64″ (0.4mm); ≥ ¾” (19mm): ± 3%
  • Overlaid  (HDO/MDO) : ≤13/16″ (20mm): ±1/32″ (0.8mm); ≥ 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.