Calculate bitumen emulsion quantity for tack coat application between asphalt layers. Enter area and application rate to get total litres and residual bitumen.
Tack coat is a thin bitumen emulsion spray applied between asphalt layers to ensure proper bonding. Without it, layers can delaminate and slip under traffic.
0.2–0.4 L/m² for new or milled surfaces. 0.3–0.6 L/m² for oxidised or concrete surfaces. Rates refer to emulsion, not residual bitumen.
CSS-1h (Cationic Slow-Setting) is most common for tack coat. Typically 57–65% residual bitumen content. Can be diluted 1:1 with water for lighter applications.
Enter area and rate to calculate
Application rates refer to undiluted emulsion quantity applied. Allow emulsion to break before overlaying.
| Surface Type | Application Rate (L/m²) | Emulsion Type | Notes |
|---|---|---|---|
| Milled surface (fresh) | 0.3–0.5 | SS-1h undiluted | High texture, needs good penetration |
| Existing HMA (good condition) | 0.2–0.3 | CSS-1h or diluted | Standard inter-layer bond |
| Existing HMA (oxidised) | 0.3–0.5 | CSS-1h undiluted | Aged surface needs more binder |
| PCC (concrete) surface | 0.4–0.6 | CSS-1h or RS-1 | Concrete binds poorly without higher rate |
| New HMA layer | 0.2–0.3 | CSS-1h diluted 1:1 | Between fresh lifts during construction |
| Bridge deck | 0.3–0.5 | Modified emulsion | May require waterproofing membrane |
Tack coat quantity is calculated directly from area and application rate. The residual bitumen content of the emulsion determines how much actual binder is delivered to the interface.
Example: A 1,000 m² road surface at 0.30 L/m²: 1,000 × 0.30 = 300 litres of emulsion. This is the total volume sprayed by the distributor truck, which is measured via the distributor meter or dip stick before and after spraying.
SS-1h emulsion at 60% residual: 300 L × 0.60 = 180 litres of residual bitumen. At 1.03 kg/L = 185 kg of bitumen binder actually delivered to the interlayer. This is the value that matters for bond strength — not the emulsion volume.
A standard bitumen distributor sprays 0.15–0.50 L/m² and holds 10,000–28,000 litres. At 0.30 L/m², a 15,000 L truck covers 50,000 m² (5 ha) per load. For a 1 km road at 7 m wide (7,000 m²), you need approximately 2,100 L — well within a single truck load. See the Rate Calculator for kg/m² rates.
Road authority specifications may quote tack coat rates as either emulsion rate (total liquid sprayed) or residual bitumen rate (actual binder delivered). A spec that says "0.18 L/m² residual" using a 60% SS-1h emulsion means you need to spray 0.18 ÷ 0.60 = 0.30 L/m² of emulsion. Always confirm with your specification whether the rate is residual or total emulsion — confusing the two causes significant over- or under-application. Use the Tonnage Calculator to estimate the overlay quantity for the same area.
Tack coat is applied between pavement layers on virtually every asphalt overlay and new pavement construction project.
Every asphalt overlay project requires tack coat on the existing pavement surface before the new layer is paved. On a 10 km resurfacing project at 8 m wide, the tack coat area is 80,000 m². At 0.25 L/m² = 20,000 litres of emulsion — about 1.5 full truck loads. Multiple lanes paved on the same day require multiple passes with the distributor. The overlay quantity can be estimated with the Material Calculator.
New pavement construction typically involves 2–3 asphalt layers: base course, binder course, and wearing course. Tack coat is required between every layer — so a 3-layer pavement needs tack coat applied twice (after base, after binder). Construction sites track tack coat volume through the distributor GPS and flow meter. Failing to apply tack coat between fresh-on-fresh lifts is a common QA non-conformance that leads to delamination under trafficking.
Bridge deck overlays require specialist tack coat systems. Bare concrete decks need a waterproofing primer coat (typically 0.3–0.5 L/m² of modified emulsion or epoxy primer) before the asphalt overlay. Steel bridge decks may use mastic asphalt or polymer-modified tack systems. Rates are higher than standard road surfaces because smooth concrete has low surface texture and requires more binder to achieve adequate bond. Always check the bridge structural engineer's overlay specification — Cost Calculator for budgeting.
Input the length and width of the area to receive tack coat, or enter the total area directly in square metres or square feet. Tack coat is applied to all existing pavement surfaces before placing a new asphalt overlay — include the full paving area including any shoulder treatments.
Enter the tack coat application rate in litres per square metre (L/m²). Standard rates are: 0.15–0.25 L/m² for smooth milled surfaces, 0.25–0.40 L/m² for existing asphalt surfaces, 0.40–0.55 L/m² for concrete or chip seal surfaces. Most road authority specs call for SS-1h or CRS-2 emulsion at 0.20–0.35 L/m² residual bitumen.
Click Calculate to get total emulsion required in litres. Convert to tank truck loads if needed (standard bitumen tankers carry 20,000–28,000 litres). Note: application rate refers to emulsion volume sprayed, not residual bitumen content — a 60% residual emulsion at 0.3 L/m² delivers 0.18 L/m² of actual bitumen.
A tack coat (also called bond coat or bitumen primer) is a thin spray application of diluted bitumen emulsion applied to an existing pavement surface before placing a new asphalt layer. Its purpose is to create a strong bond between the old and new layers, preventing interlayer slippage under traffic loads. Without adequate tack coat, new asphalt layers can delaminate and slide, leading to premature pavement failure. Tack coat is required whenever a new asphalt layer is placed on any existing surface.
The most common tack coat emulsions are SS-1h (slow-setting anionic) and CSS-1h (slow-setting cationic) at 50–60% bitumen residual content, applied at 0.15–0.40 L/m². CRS-2 (rapid-setting cationic) is used where faster breaking time is needed. For heavily trafficked roads, polymer-modified emulsions (PMBE) provide better bond strength. Most specifications require the tack coat to "break" (turn from brown to black as water evaporates) before asphalt paving can begin — typically 30 minutes to several hours depending on conditions.
Yes. Over-application of tack coat is a common problem that can actually reduce bond strength and cause bleeding. Excessive tack coat accumulates at the interface, creating a weak lubrication layer instead of a bond. It can also cause slippage of fresh asphalt under the paving machine. The correct rate is the minimum necessary to achieve uniform coverage. Most specifications require a maximum of 0.40 L/m² residual bitumen on normal asphalt surfaces.
The emulsion must fully "break" (change colour from brown/tan to black as water evaporates) before the asphalt paver can travel over it. Breaking time depends on emulsion type, air temperature, humidity, and surface conditions: SS-1h (slow-setting) typically breaks in 2–6 hours. CSS-1h (cationic slow-setting) breaks in 1–3 hours. CRS-2 (rapid-setting) breaks in 15–60 minutes and is used when the paver follows closely behind the distributor. Paving over unbroken emulsion picks the tack off the surface and transfers it to the paver undercarriage, wasting material and compromising bond.
A tack coat bonds two asphalt layers together (or asphalt to concrete) — it is applied to an existing paved surface. A prime coat is applied to a prepared granular or stabilised base before the first asphalt layer — its purpose is to waterproof and bind the top of the base, and to provide adhesion for the first asphalt layer. Prime coat rates are typically 0.5–1.5 L/m² of low-viscosity cutback bitumen or bitumen emulsion, and the base must fully cure before paving. In many modern pavement specifications, prime coat has been replaced by a geotextile or a light prime-seal.
The standard field verification method is the blotter test: place a sheet of blotter paper (typically 0.1 m² or 1 ft²) on the surface after the distributor passes, weigh it before and after, and calculate the mass per unit area. Most spec requirements are expressed as residual bitumen rate (kg/m² or L/m²). Modern distributors also have computer-controlled spraying systems with GPS and flow meters that log actual application rates in real time. Always calibrate the distributor nozzles before each project to ensure uniform transverse distribution across the full spray bar width.