GS MW U Panel Fastening — PM1 Washer

Junction function

Concealed GS MW U + PM1 fastening is a dedicated element of the concealed fastening system in mineral wool. The PM1 washer (item 03) = a steel component that transfers the load from the fastener to the geometry of the U panel joint.

Connection design:

1. Self-drilling fastener (item 02) screwed into the purlin (item 04) through the PM1 washer.
2. PM1 washer (item 03) = a profiled steel plate that presses the joint groove against the tongue of the adjacent panel.
3. The fastener anchors the panel from the joint side — without interfering with the visible façade.

Vs visible fastening (S/CH):

• Fewer fasteners (2 vs 3 across the width) — the load is distributed by PM1 along the entire joint length (vs point loads in S).
• PM1 is loaded in shear (wind pressure is distributed across the joint), not only in compression; hence the requirement for AISI 304 stainless steel or carbon steel with a zinc coating thicker than 80 μm.

Critical installation aspects

• Minimum 2 fasteners per panel — this is the catalogue minimum for panel heights up to 5 m + purlin spacing ≤4 m; for higher requirements the number must be increased in accordance with structural calculations.
• PM1 washer position — along the joint axis, in the middle of its length between purlins; deviation >5 mm = the washer works skewed and may break out.
• Tightening torque — 6–10 Nm (less than in S/CH, since the PM1 washer distributes the load and does not require such strong clamping); over-tightening = joint deformation and loss of tightness.
• PES tape (item 05) continuous as in S/CH — between the panel and the purlin.
• Thermographic inspection after the first winter — to check for any point thermal bridge from the fastener; the bridge at PM1 is smaller than at an S fastener (PM1 distributes heat over a larger area), but it still exists (steel within the wool).

Documentation

Technical Catalogue GS MW S/CH/U (Gór-Stal 2025), page 46 — GS MW U panel fastening detail using the PM1 washer. Scale 1:5.

Components in this junction