Installation Tolerances & Leveling
A Level Support Is Half the Install
FRP panels are manufactured to tight dimensional tolerance, but they only perform as designed if the support frame underneath is flat, level and correctly spaced. Most on-site complaints - rocking panels, rattling clips, cracked holes - trace back to out-of-tolerance framing, not the panel. This chapter sets the numerical tolerances every contractor should check before a single panel is lifted into place, per ZeAllgrate installation guidance and ISO 14122 access requirements.
Installation Tolerance Summary
| Parameter | Tolerance | Why It Matters |
|---|---|---|
| Support framing level | plus or minus 5 mm over 2 m; plus or minus 3 mm per metre | Out-of-level supports introduce eccentric point loading and rocking panels |
| Bearing surface flatness | plus or minus 2 mm per 1 m on the support flange | A high spot crushes the panel edge; a low spot leaves a floating bearing |
| Minimum bearing length - molded | 50 mm on the support at each end | Less than this risks edge shear-out and poor clip purchase |
| Minimum bearing length - pultruded | 75 mm on the support at each end | Pultruded bearing bars need a wider seat to control web crippling |
| Panel gap for thermal movement | 3-5 mm standard between panels; calculate Delta L = L x alpha x Delta T | Prevents summer buckling and winter rattling |
| Clip placement tolerance | plus or minus 10 mm from the specified position | Keeps clips at support intersections where they belong |
| Hole diameter clearance | Bolt diameter + 1.5 mm | Provides sliding room for thermal movement |
| Minimum edge distance | 2.5 x bolt diameter (and at least 50 mm from panel edge) | Prevents shear-out failure at the hole |
| Maximum shim stack | 3 mm total under any panel edge | Thicker shim stacks are unstable and invite rocking |
Bearing Length and Thermal Gap
Seat the Panel Properly
A molded panel bears on 50 mm minimum; a pultruded panel needs 75 mm. If the support flange is narrower, the panel overhangs and the bearing-bar end reacts on a small edge - check the steel angle width before ordering clips.
Calculate the Gap
Reserve a 3-5 mm nominal gap between panel ends, then verify with Delta L = L x alpha x Delta T. For a 3 m pultruded run at alpha = 20 x 10^-6 /C and a 50 C seasonal swing, Delta L = 3 mm - the standard gap already covers it.
Leveling with Shims - What to Use and What to Avoid
| Shim Material | Use? | Note |
|---|---|---|
| FRP flat bar / pultruded shim | Yes | Matches CTE, corrosion-proof, cut to thickness on site |
| Stainless steel shim (304/316) | Yes | Good for small height adjustments; isolate from FRP with a nylon/EPDM pad |
| Galvanized steel shim | Limited | Indoor dry use only; corrodes and stains in wet/chloride service |
| Wood, plywood, hardboard | No | Compresses, rots, absorbs water; creates a soft, unstable bearing |
| Rubber / soft plastic packer | No | Creeps under sustained load; the panel will sink over time |
Stack no more than 3 mm total shim thickness under any panel edge. If the support is more than 3 mm out of level, grind down the high spot or pack the support itself - never stack shims to force a level panel.
Common Fit-Up Errors and the Fix
| Symptom | Cause | Fix |
|---|---|---|
| Panel rocks when walked on | High spot on support flange or low spot at one bearing | Mark the gap with a feeler gauge; grind the high spot or shim the low spot |
| Panel end overhangs support | Support flange too narrow or panel shifted | Re-seat to 50/75 mm minimum bearing; reposition clip |
| Panels touch in summer / gap in winter | Thermal gap too small or too large | Re-cut end gap to Delta L allowance; use sliding clips |
| Cracks radiating from clip holes | Edge distance too small or over-torqued | Relocate hole, increase edge distance to 2.5 x bolt diameter, torque by hand |
| Panel rattles on supports | Loose clips or no clip at an intersection | Add a clip at every support intersection; do not over-tighten |
| Water pools on panel | Panel sloped the wrong way / frame out of level | Re-level support; molded panels are flat - drainage is by fall of the frame |
Leveling Tools on Site
Laser Level
Sweep a level datum across the frame before installation; fastest way to map high and low spots over a long run.
Spirit Level (1-2 m)
Check each support flange and the laid panel; verify plus or minus 5 mm over 2 m.
Feeler Gauges
Measure the actual gap between panel and support at each bearing - the only way to quantify rocking.
Tape Measure
Confirm bearing length, clip spacing and end gaps before fastening.
Torque Wrench
Set to the clip manufacturer value; never use an impact wrench on FRP.
Carpenter's Line / String
Straighten long runs and check camber between supports.
Pre-Installation Checklist
| Check | Acceptance Criterion | Status |
|---|---|---|
| Support structure verified | Frame level within plus or minus 5 mm over 2 m; flatness within plus or minus 2 mm/m | OK / action |
| Support spacing confirmed | Clear span matches the certified load/span chart; bearing bars oriented across span | OK / action |
| Bearing width adequate | At least 50 mm molded / 75 mm pultruded on the support flange | OK / action |
| Panels inspected | No shipping cracks, chipped edges or delamination; resin colour matches order | OK / action |
| Clips and fasteners counted | Min 4 per panel, spacing no more than 1219 mm; correct SS304/316 material | OK / action |
| Thermal gaps planned | 3-5 mm nominal end gap; clearance around columns and obstructions | OK / action |
| Tools calibrated | Torque wrench, laser level, feeler gauges on site and functional | OK / action |
| Shims available | FRP or stainless shims on site; no wood packers in the installation kit | OK / action |
Need an Installation Tolerance Checklist for Site?
Send the span, panel type and support section - ZeAllgrate returns a tolerance sheet and clip schedule.
Source: ZeAllgrate (Fiberglass Grating Manufacturers Council / ACMA) design guidelines; ASTM International; ISO 14122; OSHA 29 CFR 1910. Indicative data for specification guidance only — final design verified by ZeAllgrate engineering against certified load/span charts.