Asphalt Tack Sprayer Product

Overview

Asphalt tack coat sprayers apply hot bituminous emulsion (liquid asphalt cement mixed with water) onto prepared pavement surfaces immediately before laying new asphalt or chip seal. The tack coat acts as an adhesive, bonding the new layer to the existing pavement and preventing delamination (separation of layers). The system heats the emulsion to 160–200°F to reduce viscosity (thickness) for optimal spray atomization and adhesion, then spray applies at a controlled rate (0.1–0.4 gallons per square yard) using a Spray Bar Assembly articulated boom with proportional pressure control.

Road resurfacing projects (overlays, seal coats, friction courses) depend on tack coat application; poor or absent tack causes premature pavement failure, with cracks appearing within 1–2 years. Professional contractors specify tack application as a critical quality step, and DOT specifications mandate documentation of coverage and temperature.

Emulsion types and properties

Bituminous emulsions used as tack coats are suspensions of asphalt droplets in water, stabilized by chemical surfactants. Common types:

CSS-1 (Cationic Slow Set): Highest viscosity (thickest), typically 120–150 Saybolt Furol seconds (SFS) at 77°F. Designed for spray application at high air/pavement temperatures (>80°F), allowing emulsion to break (water evaporates, asphalt droplets coalesce) before traffic loads the new layer. Most common tack coat on highways.

CQS-1 (Cationic Quick Set): Lower viscosity (80–120 SFS), breaks faster (~30 minutes), used on cooler days or when rapid set is needed for traffic control.

CMS-2 (Cationic Medium Set): Very high viscosity, used for aggregate seal coats where thick, sticky emulsion ensures chip adhesion.

The Heated Emulsion Tank maintains emulsion at 160–180°F (optimal for CSS-1, 120–150 SFS), reducing viscosity to ~10–20 SFS at spray temperature, allowing fine atomization (droplet size <100 microns) for even coverage.

Heating and temperature control

The Heating and Burner Assembly diesel or LPG immersion burner heats emulsion in the Heated Emulsion Tank insulated tank. The asphalt-tack-sprayer-immersion-burner burner tube (typically 2–3 inches diameter, 6–10 feet long) extends into the tank, transferring heat directly to the emulsion. A Combustion Air Blower forced-draft air blower ensures complete combustion (no carbon monoxide, no smoke), and a Flame Safety Sensor UV safety sensor shuts off fuel flow if the flame fails.

The Temperature Control proportional controller maintains tank temperature ±5°F by modulating burner on/off cycles. A Temperature Sensor RTD temperature sensor continuously monitors sump (lowest point of tank) temperature; if sump exceeds 200°F, the thermostat reduces burner duty to prevent thermal cracking (oxidation degradation) of the asphalt.

Heating rate is typically 50–80°F per minute; warming a 2,000-liter tank from ambient (60°F) to operating temperature (170°F) takes 1–2 hours before spraying begins. During operation, the burner maintains temperature against cooling losses, typically cycling 30–50% duty cycle on an active job.

Spray application system

The Emulsion Supply Pump gear pump (12–20 GPM @ 100 PSI) draws hot emulsion from the Suction Strainer filtered inlet, maintaining suction pressure <3 PSI to avoid cavitation (bubbles forming, reducing flow and damaging pump). The pump discharge hose routes pressure through the Pressure Gauge pressure gauge to the Spray Bar Assembly articulated boom.

The Spray Bar Assembly 25–35 foot boom extends across the lane width (two lanes typical); the boom can articulate up/down (±30°) via Articulation Cylinders double-acting cylinders, allowing coverage of crowned or superelevated pavements. The boom's Spray Nozzle Tips 12–16 flat-fan spray nozzles (80° spray pattern, 0.8–1.0 mm orifice) atomize the hot emulsion, creating a fine spray mist that settles evenly across pavement.

The operator controls spray application rate via Operator Control Panel variable frequency drive (VFD) modulating pump speed: 50% VFD = 6–10 GPM output, 100% VFD = 12–20 GPM output. Combined with truck travel speed (0.5–5 mph typical), this allows precise application rates: 0.1 gal/sq yd (very light tack, 20 GPM @ 3 mph) to 0.4 gal/sq yd (heavy tack, 12 GPM @ 1 mph).

Operational workflow

The tack coat spraying crew consists of three people: truck operator, nozzle/pressure monitor, and traffic control. The truck is positioned at one end of the segment to be tacked (typically 0.5–2 miles for a single load). The operator engages the pump (via VFD control) and begins moving forward at a pre-calculated speed (e.g., 1.5 mph) to achieve the target application rate (e.g., 0.2 gal/sq yd).

The boom is kept at a constant height above the pavement (12–24 inches typical) to maintain even coverage; uneven boom height causes dry spots (high boom, emulsion evaporates before settling) or puddling (low boom, too much application). The monitor observes spray pattern and pressure, alerting the operator to nozzle clogs (uneven pattern, missing boom section) or pressure loss (pump cavitation).

Tack coat application must occur on a clean, dry pavement. Any dust, loose gravel, or moisture prevents emulsion adhesion. Many projects specify 24 hours of dry weather before tack application; if rain occurs after tack and before overlay, the job is scrubbed (wet asphalt won't bond), and the tack coat is chemically removed before re-tacking.

Quality control and inspection

Tack coat coverage is verified by visual inspection (even brown color across pavement, no dry spots) and by adhesion testing: a tack coat is considered properly set when a fingernail scraped across the surface leaves no visible mark and emulsion does not transfer to the finger. Setting time is 1–4 hours depending on temperature, humidity, and emulsion type; trucks must remain off tacked pavement until set.

Hot-mix asphalt (new overlay) must be placed within 24 hours of tack application; older tack becomes dusty and loses adhesion. DOT specifications mandate documented temperature records (thermostat readout photographs) and application rate verification (gallons used divided by lane-miles covered).

Equipment maintenance

The Heated Emulsion Tank tank interior requires periodic cleaning (semi-annually or annually) to remove hardened asphalt residue (oxidized emulsion that builds up as thick coating). Tank cleaning involves heating to 180°F and circulating solvents (diesel, mineral spirits) through the pump and spray lines, flushing dissolved asphalt to waste. Neglected cleaning reduces heating efficiency and can cause thermal runaway (uncontrolled temperature rise).

Spray tips are the most consumable item; worn tips (orifice enlarged from abrasion) cause uneven patterns and higher flow rates. Tips are typically replaced after 100–200 lane-miles of operation (~$2–5 per tip, set of 12 = $25–60 per truck per season).

The Heating and Burner Assembly burner nozzles and electrodes require annual inspection; carbon buildup reduces ignition reliability and flame quality. Professional maintenance contracts (typically $500–1,500/year) include burner service, tank cleaning, and seasonal safety inspections.

Environmental and safety

Hot bituminous emulsion (160–200°F) poses burn hazard to operators; spray suits (fire-resistant coveralls) and gloves are standard PPE. The asphalt-tack-sprayer-pump-system pressure system (100 PSI) can cause injection injury if operators contact spray nozzles; lockout/tagout procedure is required before nozzle maintenance.

Emulsion odor (mineral oil, bitumen), though generally innocuous, can cause headaches in operators during prolonged exposure; adequate ventilation and dust masks are recommended. Disposal of residual emulsion (tank cleanings, spills) requires containment; emulsion is hazardous waste in most states and cannot be discharged to storm drains. Tank cleanings are collected in drums and disposed at licensed hazardous waste facilities (~$200–500 per tank).

Tack coat overspray onto adjacent pavement (non-target areas, pedestrian walkways, adjacent lanes) causes safety hazards (slippery surfaces) and staining. Accurate boom positioning and variable nozzle shutoff systems reduce overspray; manual overspray cleanup (solvent flushing) costs $200–400 per incident.