Paving Fabric - Stress Absorbing Membrane Interlayer (SAMI)

Surface preparation - Remove water, grass, weeds, grease and any other material that would prevent bonding, and sweep the surface clean of all loose material. Blowing cracks out with compressed air is ideal. Prefill cracks wider than 7 mm with a hot sealant, and repair potholes, failed patches and depressions beforehand - allow cold emulsion-based repairs about a week to cure; hot mix patching needs no waiting period. The fabric mitigates cracking but does not substitute for repairing structural failure.

Tack coat - Spray a uniform bitumen emulsion or warm-applied binder using a calibrated distributor, set to cover 100 mm wider than the fabric. The fabric absorbs 1.0 ℓ/m² by itself, so the rate must exceed that to saturate the fabric and bond it to both layers - increase it further on cracked, weathered or open-textured surfaces, which draw more binder than a tight surface. Under-application is the most common cause of failure: an unsaturated fabric neither waterproofs nor bonds. Avoid cutback bitumen entirely, as the solvents become trapped in the fabric and cause bleeding and slippage later.

Placement - Roll out the fabric onto the tack coat, preferably with a mechanical laydown device to reduce wrinkles, before the binder loses its tackiness. Where emulsion is used under an asphalt overlay, allow it to break first. Work out creases with a squeegee or the reverse of a hard broom; cut stubborn folds open, apply extra binder to one side and overlap. Overlaps and joins should be 100–150 mm. Spraying binder 150 mm beyond the edge of the first width means the overlap is saturated when the next width is laid over it.

Rolling - Roll with a pneumatic tyred roller, three to four passes, once the tack coat has set sufficiently to avoid pick-up. Delay rolling if pick-up still occurs, and keep the tyres clean and free of binder. Rolling seats the fabric into the tack coat and removes remaining wrinkles. Where the overlay is delayed or traffic must cross the fabric, blind the surface with washed coarse river sand or 4 mm stone to prevent pick-up, keep speeds low, and avoid sharp turning or heavy braking.

Overlay and constraints - Place the asphalt overlay according to normal design procedure. Feed mix beneath the paver rather than allowing it to push the fabric, and repair any displacement or damage before continuing. Note the binder constraint throughout: the fabric melts at 150°C, so emulsion or warm-applied binders are required - hot penetration-grade bitumen, SBR-modified hot bitumen and bitumen rubber are all applied above that temperature and are unsuitable. Not recommended at intersections or sharp bends where braking and turning forces are high, or where vertical movement across a crack is severe enough to tear the fabric.