Undercut Anchors for Stone and Porcelain Cladding

What it is

A rear-fixed anchor set into a conically undercut hole drilled part-way into the back of a stone or porcelain panel. The anchor grips the shoulder of the cone mechanically, with no expansion force against the panel.

Nothing shows on the face of the panel.

Specification at a glance

Property	Typical specification
Anchor material	Stainless, grade by exposure
Hole	Conical undercut, purpose-drilled
Depth	Part-way through; never breaking the face
Panel thickness	Minimum set by anchor and stone strength
Testing	Pull-out to ASTM C1354 on the supplied batch
Edge distance	Governed by the system; verified per panel size

Why it replaced kerf fixing

Kerf fixing cuts a slot into the panel edge and slides a clip into it. It works, but it relies on the strength of the slab edge, which is the weakest part of the panel and the part most likely to have been chipped in handling.

Undercut anchors move the load path to the back of the panel, away from the edges. That allows thinner panels, larger formats and cleaner joints, and it removes the edge as the failure point.

The quality chain

Step	What must be right
Stone selection	Tested flexural and compressive values, this batch
Hole drilling	Depth, angle and cone geometry within tolerance
Anchor setting	Correct torque, fully engaged
Testing	Pull-out on production panels, not just samples
Installation	Each panel independently supported

Where projects go wrong

• Hand drilling instead of a rigged drill with a depth stop.
• Test values borrowed from another project or from quarry literature.
• Panels too thin for the anchor system chosen.
• Edge distances reduced to suit a panel layout, without recalculation.
• 304 stainless anchors in coastal exposure, where 316 is required.

Standards referenced

Stone anchorage strength testing to ASTM C1354. Stone identification under IS 1123. Wind loading the anchorage must resist under IS 875 (Part 3).