Bituminous vs Polyurethane Waterproofing: What You Should Know?

Written By Adam Paul - Waterproofing Expert

Bituminous waterproofing and polyurethane waterproofing are two of the most used waterproofing membranes, and they are used to protect buildings from water and moisture penetration. In order to choose the right type of the waterproofing membrane, you should know the differences between them before you apply. 

So as waterproofing experts, Aqviz, we prepared a complete comparison guide by considering the bituminous vs polyurethane waterproofing.  We have included main differences in material composition, water resistance, breathability, flexibility, chemical resistance, and UV resistance. As minor differences, we included adhesion, tear resistance, seam integrity, root penetration resistance, eco-friendliness, fire resistance, anti-slip resistance, toxicity and self-expanding capability. 

Material Properties Comparisons Between Bituminous and Polyurethane Waterproofing?

These are the material composition, performance, durability, and environmental resistance comparisons between bituminous and polyurethane waterproofing

1. Bituminous waterproofing is a petroleum-based, bitumen-derived membrane while polyurethane is composed of synthetic polymers derived from a reaction between polyols and isocyanates.
2. Bituminous and polyurethane are highly water resistant.
3. Bituminous has a lower breathability while polyurethane has a higher breathability
4. Bituminous is less flexible than polyurethane waterproofing
5. Bituminous waterproofing has a moderate chemical resistance compared to polyurethane waterproofing.
6. Bituminous waterproofing has poor UV resistance, while polyurethane has a higher UV resistance.

Composition Difference between Bituminous and Polyurethane Waterproofing

Bituminous waterproofing is a petroleum-based, bitumen derived membrane while Polyurethane is composed of synthetic polymers derived from a reaction between polyols and isocyanates.

Bituminous waterproofing is a petroleum-based, bitumen derived membrane. It consists of bitumen mixed with polymers and reinforced with fabrics or fiberglass to create a flexible and durable waterproof membrane.

Polyurethane waterproofing is composed of synthetic polymers derived from a reaction between polyols and isocyanates. It forms a seamless, super elongated elastomeric membrane when it is applied on the substrate. 

Water Resistance Difference between Bituminous and Polyurethane Waterproofing

Bituminous and polyurethane are highly water resistant.

Bituminous waterproofing provides superior water repellency due to its non-porous, petroleum-based nature. It is excellent for flat roofs, foundations, and underground structures, where continuous exposure to moisture is expected. The key reason for its superior resistance is its hydrophobic (water-repelling) nature, which prevents water absorption and penetration.

Polyurethane waterproofing, however, provides superior water resistance, over time without any crack or damage due to its elastic nature. It can withstand various weather conditions and even under small structure movements. 

There are more than 10 types of waterproofing membranes available for building waterproofing. You can read all of the 10 Types of Waterproofing Membranes with their properties, applications, pros, and cons in this guide.

Breathability Differences between Bituminous and Polyurethane Waterproofing

Bituminous has a lower breathability while polyurethane has a higher breathability

Bituminous waterproofing has a lower breathability. It forms a completely sealed, non-permeable layer, preventing both water and vapor from passing through. This characteristic makes it effective for roofing and underground applications, but in enclosed spaces like basements, improper application can trap moisture, leading to condensation issues.

But polyurethane waterproofing has a higher breathability.  It allows to evaporate trapped moisture in the layer. It helps to reduce the condensation and minimize the mold growth and structural damages over time due to vapor.

Flexibility Difference between Bituminous and Polyurethane Waterproofing

Bituminous is less flexible than polyurethane waterproofing

Bituminous waterproofing is less flexible compared to polyurethane waterproofing. Bituminous waterproofing can withstand structural movements and temperature changes without cracking, due to its flexibility. But in the colder temperatures, it can be cracked due to lower temperatures. The bituminous membrane flexibility depends on the polymer content, and it allows to stretch and contract without losing adhesion on the substrate. It helps to use bituminous waterproofing on roofs, bridges, and areas with thermal expansion. 

Polyurethane waterproofing is more flexible than bituminous waterproofing. It has a superior elongation capacity  (up to 600%) even at the low temperature. Hence it can be used for building waterproofing even in low temperatures and small movements. 

Chemical Resistance Difference Between Bituminous and Polyurethane Waterproofing

Bituminous waterproofing has a moderate chemical resistance compared to polyurethane waterproofing.

Bituminous waterproofing has a lower chemical resistance than polyurethane. Bituminous waterproofing resistance against common acids, alkalis, and salts. But it can deteriorate when it is exposed to solvents or hydrocarbons. 

Polyurethane waterproofing has a higher chemical resistance than bituminous waterproofing. Polyurethane waterproofing is resistant to aggressive chemicals, solvents, and oils, due to their chemically inert polymeric structure. Hence, it can be used for many chemical based substrate structures. 

UV Resistance Difference Between Bituminous and Polyurethane Waterproofing

Bituminous waterproofing has poor UV resistance, while polyurethane has a higher UV resistance.

Bituminous waterproofing has a poor UV resistance. When it is exposed to sunlight, it causes oxidation, brittleness, and surface cracking, reducing its lifespan over time. In order to improve UV protection, a protective layer like aluminum foil, gravel, or a UV-resistant coating is often applied over bituminous membranes. Without this protection, bituminous coatings deteriorate faster, leading to potential waterproofing failure.

Polyurethane waterproofing has outstanding UV resistance. It can withstand stable with maintaining elasticity, color stability and protective performance over time due to its inherent UV-resistant additives in its chemical formulation.

Read our similar expert guide related to bituminous waterproofing

• Cementitious vs Bituminous waterproofing
• Cementitious vs Polyurethane waterproofing

Functional and Environmental Impact Comparisons Between Bituminous and Polyurethane Waterproofing

These are the mechanical strength, safety, environmental impact, and usability comparisons between bituminous and polyurethane waterproofing