How is formwork pressure calculated?
Fresh concrete lateral pressure is calculated by the project's formwork engineer to the governing standard — ACI 347 in the United States, CIRIA Report 108 in the United Kingdom, or DIN 18218 in the German-speaking countries. The calculation accounts for the rate of rise (pour speed), concrete temperature, consistency and admixtures, vibration, and reinforcement. It is not something to estimate off a generic table; the engineer designs and checks the form.
How thick should formwork plywood be?
Across most vertical formwork, 18 mm is the common baseline because it suits typical bearer spacing and holds its line under normal pours. Specifiers commonly move to 21 mm for fair-face surfaces, large panels, or wider bearer spacing, where the extra stiffness keeps the face flat. Thickness is one input; the formwork designer sizes the whole system to the calculated pressure and required finish.
What causes a wavy or uneven concrete face?
A wavy face usually comes from panel deflection — the plywood bowing between its bearers under concrete pressure. If the support spacing is too wide for the panel stiffness, the sheet bellies out and telegraphs that curve into the concrete. Tighter bearer spacing or a stiffer, thicker panel controls it, which is why fair-face work drives closer support spacing.
How far apart can form ties be spaced?
Form tie spacing is engineered, not chosen off a chart. The ties carry the wall pressure back across the form, so their layout is designed to the calculated fresh-concrete pressure for that pour. Closer support lets a thinner panel work; wider support demands a stiffer, thicker panel. The formwork designer sets the tie and bearer layout as a system.
Which adhesive class should formwork plywood use?
Match the bond class to the expected number of pours. Phenolic-bonded panels to EN 636-3 (Pro Form, HDO range) sit at the top of the reuse envelope for high-rotation and fair-face work. Melamine core-resin (WBP MUF) panels to EN 636-2 (Form Basic, Form Extra) serve lighter rotation well. Reuse figures are maximums — read "up to N reuses," not a guaranteed minimum.
