APP modified bitumen membrane is a high-performance waterproofing sheet produced by blending atactic polypropylene with penetration-grade bitumen. The polymer raises the binder’s heat resistance, UV stability and mechanical strength — making APP membranes the standard choice for exposed roofing in warm and temperate climates, where an unmodified or elastomeric sheet would soften, flow or degrade under direct sun.
RAHA Gilsonite Co. supplies the raw materials behind membrane manufacturing: gilsonite as a hardness and compatibility modifier, and oxidized bitumen grades as the base binder. This page covers APP membrane technology, why gilsonite dosage is higher in APP compounds than in SBS, and how the two systems compare.
What is APP Modification?
Atactic polypropylene is a plastomeric thermoplastic. Blended into bitumen at 25–35% by weight — roughly twice the loading used in SBS compounds — it forms a plastic phase that dominates the binder’s high-temperature behaviour:
- Softening point raised to as high as 155 °C, against roughly 50 °C for unmodified bitumen
- Improved UV and oxidation resistance
- Greater dimensional stability at elevated temperature
- Enhanced tensile strength
Plastomer versus elastomer. APP is a plastomer: it holds its shape under heat but does not spring back after stretching. SBS is an elastomer: it recovers. That single difference drives every other distinction between the two membranes — including, as the next section explains, how much gilsonite each compound can take.
Technical Specifications
| Property | Typical Value | Test Method |
|---|---|---|
| Softening point | 145–155 °C | ASTM D36 |
| Cold flexibility | −5 to −10 °C | EN 1109 |
| Tensile strength (L/T) | ≥ 800 / 600 N per 50 mm | EN 12311-1 |
| Elongation at break | ≥ 30% | EN 12311-1 |
| Heat resistance | 130 °C | EN 1110 |
| Water impermeability | Pass at 200 kPa | EN 1928 |
| Thickness | 3–5 mm | EN 1849-1 |
| Carrier | Polyester / fiberglass / composite | — |
Gilsonite in APP Membrane Compounds
Gilsonite — natural asphaltite — is a hardness and softening-point modifier. In an APP compound its effect works with the polymer rather than against it, which is why APP formulations carry gilsonite more readily than SBS formulations do.
Why dosage is higher here than in SBS
An SBS membrane is formulated for low-temperature elasticity, and gilsonite is a stiffening agent — above a modest dosage the two objectives collide. An APP membrane is formulated for heat resistance and dimensional stability, and stiffening is exactly what is wanted. The same additive that constrains an SBS compound reinforces an APP one.
What gilsonite contributes to APP compounds
- Raises softening point further, reinforcing the property APP is chosen for
- Improves UV and weathering resistance through its high asphaltene content
- Increases surface hardness and resistance to mechanical damage on exposed roofs
- Reduces polymer load — part of the stiffening otherwise requiring more APP
- Improves filler dispersion and compound homogeneity
- Enhances adhesion to substrates and between plies
Practical guidance. Because APP already has limited cold flexibility (−5 to −10 °C), that figure is the property to watch when raising gilsonite dosage. Validate EN 1109 on trial batches, and keep the installation climate in mind — a compound optimized for Gulf rooftops will not suit a Mediterranean winter installation.
For the material data behind formulation work, see gilsonite specification, chemical characterization, and technical advantages of gilsonite.
Base Bitumen Grades Used in Membrane Production
APP compounds generally start from a harder base than SBS compounds, since the target softening point is higher. Membrane manufacturers select from oxidized bitumen grades:
| Grade | Softening Point | Typical Membrane Use |
|---|---|---|
| Oxidized Bitumen 115/15 | 110–120 °C | High-temperature APP compounds |
| Oxidized Bitumen 105/15 | 100–110 °C | Hard compounds, exposed roofing |
| Oxidized Bitumen 105/35 | 100–110 °C | General membrane and sheet production |
| Oxidized Bitumen 90/10 | 85–95 °C | Softer compounds, temperate climates |
Related reading: gilsonite and bitumen · gilsonite in construction
Key Applications
Exposed roofing systems
APP membranes suit exposed single-ply and multi-ply roofing where UV resistance and heat stability decide service life: industrial and commercial flat roofs, terraces and podium decks, and installations across the Middle East, the Mediterranean and South Asia.
Bridge deck waterproofing
The high softening point lets an APP membrane survive the heat of asphalt overlay placement — a condition that would damage a lower-softening-point sheet during construction.
Parking deck waterproofing
Mechanical strength and surface hardness give APP membranes durable, traffic-resistant performance on exposed and covered parking decks.
Below-grade applications
APP membranes also serve below-grade waterproofing where high hydrostatic pressure resistance is required, though SBS is generally preferred where structural movement is expected.
APP vs SBS — When to Choose Each
| Criterion | Choose APP | Choose SBS |
|---|---|---|
| Climate | Hot / temperate | Cold / temperate |
| UV exposure | Exposed roofing | Covered / protected |
| Temperature priority | High heat resistance | High cold flexibility |
| Installation | Torch-applied | Torch or self-adhesive |
| Movement accommodation | Moderate | High |
| Green roof | Acceptable | Preferred |
| Polymer loading | 25–35% | 12–15% |
| Gilsonite dosage | Higher — stiffening is desirable | Low — supporting role |
For the SBS side of the comparison, see SBS membrane.
Advantages of APP Membrane
- Superior heat resistance — stable to 130 °C
- Excellent UV resistance, suited to fully exposed installation
- High tensile strength and resistance to mechanical damage
- Torch-applied — fast, well-established installation method
- Long service life — 25 to 30 years in exposed conditions
- Wide availability in standard 1 m × 10 m rolls
- Accepts higher gilsonite dosage, reducing polymer cost per tonne
Quality Standards
| Standard | Scope |
|---|---|
| EN 13707 | Reinforced bitumen sheets for roof waterproofing |
| ASTM D6222 | APP modified bituminous sheet materials |
| EN 1928 | Water impermeability |
| EN 1109 | Flexibility at low temperature |
| EN 1110 | Heat resistance |
| EN 12311-1 | Tensile properties |
Frequently Asked Questions
APP compounds accept more gilsonite than SBS compounds because stiffening reinforces rather than undermines the membrane’s purpose. The limiting factor is cold flexibility, which is already modest in APP at −5 to −10 °C, so EN 1109 should be verified on trial batches as dosage rises.
APP uses a plastomeric polymer giving high heat resistance and UV stability, suited to exposed roofs in hot climates. SBS uses an elastomeric polymer giving elastic recovery and cold flexibility, suited to cold climates and structures that move. APP holds its shape under heat; SBS springs back after stretching.
APP compounds generally start from a harder base than SBS, since the target softening point is higher. Oxidized grades such as 115/15 and 105/15 are common for high-temperature and exposed-roofing compounds, with softer grades used for temperate climates.
They can be installed in cold climates, but cold flexibility of −5 to −10 °C limits performance where freeze-thaw cycling and structural movement are significant. SBS is the better choice in those conditions.
RAHA Gilsonite Co. supplies the raw materials used in membrane manufacturing — gilsonite as a modifier and oxidized bitumen grades as the base binder. Contact us with your formulation requirements for specification sheets and pricing.
Raw Materials for Membrane Production
Gilsonite and oxidized bitumen grades supplied from Dubai and Ankara offices. Specification sheets, samples, and quotations available on request.
Related pages: SBS Membrane · What is Gilsonite? · Oxidized Bitumen Grades · Gilsonite in Construction · Gilsonite Price
