Asphalt waterproofing is one of the most reliable waterproofing methods available, with a proven track record spanning over 100 years since the Taisho era, widely used for rooftop waterproofing on condominiums and commercial buildings.
This article covers a comparison of the three asphalt waterproofing methods, differences in service life compared to other waterproofing systems, maintenance timing and procedures, types of renovation methods, and key points for selecting a contractor.
What Is Asphalt Waterproofing?
It is a method that forms a waterproof layer by combining molten asphalt with asphalt sheets. By combining liquid-applied waterproofing (applied by coating) and sheet waterproofing (applied by bonding), it achieves a high level of water resistance. It is also compatible with rooftop greening and is known for consistently stable installation quality.
Features, Advantages, and Disadvantages of the Three Methods
| Hot Method | Torch Method | Cold Method (Ambient Temperature Method) | |
|---|---|---|---|
| Application Method | Asphalt is melted in a kettle and roofing sheets are bonded together | Modified sheets are heated and bonded using a torch burner | Self-adhesive sheets with a rubber-asphalt adhesive layer are applied |
| Open Flame Use | Yes (kettle used) | Yes (burner used) | No |
| Odor & Smoke | Significant | Minimal | None |
| Service Life | 17+ years | 15–25 years | 15–20 years |
| Advantages | Fast curing, 100+ years of proven use, high watertightness and durability | Efficient (melting and bonding done simultaneously), reduced risk of burns | No odor or smoke, ideal for densely populated residential areas, environmentally friendly |
| Disadvantages | Produces odor and smoke, risk of burns for workers | Poor workmanship can accelerate deterioration (heavily dependent on the skill of the installer) | Waterproof layer becomes thick and heavy, increasing structural load |
| Common Applications | Rooftops of large commercial buildings and condominiums | The most widely used method | Densely populated urban residential areas |
Asphalt Waterproofing vs. Other Methods | Service Life Comparison
| Waterproofing Method | Service Life | Cost | Features |
|---|---|---|---|
| Asphalt Waterproofing | 15–30 years | High | Multiple layers resist deterioration. Highest reliability |
| Sheet Waterproofing | 10–15 years | Low | Easy to install with shorter construction time. Simply involves laying sheets |
| Urethane Waterproofing | 10–15 years | Low | Adaptable to complex shapes. Requires frequent maintenance |
While asphalt waterproofing has higher upfront costs, its service life is approximately twice that of other methods, making it possible to reduce long-term maintenance expenses.
6 Deterioration Signs That Indicate Maintenance Is Needed
- Cracking — Fissures in the protective concrete or surface of the waterproof layer, directly leading to water leaks
- Ponding water — Poor drainage caused by faulty installation or floor warping, which accelerates deterioration of the waterproof layer
- Water leaks — The final stage when deterioration has been left unaddressed; complete re-waterproofing is required
- Blistering — Air or water infiltrating due to poor adhesion to the substrate, leading to rupture of the waterproof layer
- Weed growth — Soil accumulation around drains allows roots to penetrate the waterproof layer; attempting to pull weeds yourself risks damaging it
- Cracks and leaks around drains — Water infiltrates through cracks around drain openings; prompt action is required
Self-Inspection Checklist
If any of the following conditions apply, we recommend consulting a professional contractor.
- □ Water leaks are occurring
- □ Long horizontal cracks are visible on exterior walls
- □ Knocking on the concrete produces a hollow, dry sound
- □ The waterproof layer shows tears or peeling
- □ Cracks or weed growth are present around drains
- □ The waterproofing sheet is bulging
- □ The waterproofed surface has turned whitish or powdery
- □ Water has begun pooling on the asphalt surface
3 Ways to Extend the Life of Your Waterproofing
① Repair Deterioration While the Affected Area Is Still Small
Leaving minor cracks or blistering unaddressed can eventually require large-scale renovation involving complete removal of the existing waterproof layer. Early repairs directly reduce total costs and extend the building's lifespan.
② Regular Top Coat Reapplication (Every 5 Years)
The top coat is the outermost protective layer over the waterproofing system. Reapplying it every 5 years extends the overall maintenance cycle of the waterproof layer. Compared to full waterproofing work, this requires less effort and cost, making it a highly cost-effective maintenance measure.
③ Regular Cleaning of Drains
When drains become clogged with debris, fallen leaves, or soil, rainwater cannot drain properly, leading to ponding and accelerated deterioration of the waterproof layer. Drain cleaning is a routine maintenance task that building managers or residents can carry out themselves.
3 Types of Renovation Methods
| Method | Description | Best Suited For |
|---|---|---|
| Overlay Method | A new waterproof layer is installed over the existing one | When the existing layer still retains some waterproofing function |
| Removal Method | The existing waterproof layer is fully removed and replaced | When deterioration is severe and the existing layer can no longer be used |
| Regeneration Method | A new waterproof layer is bonded over the existing one to form a unified system | When drilling into the substrate is undesirable; lower risk of leaks during construction |
4 Key Points for Selecting a Waterproofing Contractor
- Verify experience and track record — Check the contractor's website for the types of work they specialize in and their portfolio of completed projects
- Scrutinize the quotation — Confirm that the work scope, dimensions, and unit prices are clearly itemized rather than listed as a lump sum
- Obtain quotes from at least three contractors — Compare costs and the appropriateness of the proposed work
- Choose a company that handles its own construction — This eliminates intermediary markups, reducing costs, and allows for direct communication, providing greater peace of mind
Recommended Inspection Frequency
For buildings owned by Osaka Prefecture, facility managers are required to conduct visual inspections once per year. It is advisable for condominiums and apartment buildings to follow the same schedule. For areas with a risk of falls, such as rooftops, please engage a qualified professional contractor with proper safety management protocols.
Summary
Asphalt waterproofing offers the longest service life among waterproofing methods, ranging from 15 to 30 years. However, precisely because of its long lifespan, there is a risk that maintenance may be neglected. By consistently performing regular self-inspections, reapplying the top coat, and cleaning drains, you can maximize the longevity of your waterproofing.
INA&Associates Co., Ltd. provides comprehensive rental property management services, including building maintenance for condominiums and apartment buildings. Please feel free to contact us regarding waterproofing maintenance planning and contractor selection.
