Polyurethane joint sealants dominate construction sites across South Africa, and contractors specify them by default on roads, bridges, airport aprons and industrial floors. However, the performance record of polyurethane in South Africa’s specific conditions tells a different story to the one on the data sheet. Joint sealant failure in South Africa follows a predictable pattern, and polyurethane chemistry sits at the centre of it. Furthermore, the research is unambiguous. Under direct UV exposure, polyurethane sealants deteriorate in under three years. South Africa’s highveld and coastal environments accelerate that timeline considerably. The result is cracked, failed joints, water ingress into the structure below, and maintenance cycles that never seem to end.
Why Polyurethane Is Everywhere Despite Its Limitations
Polyurethane sealants became the default joint sealant on South African construction projects for straightforward reasons. They bond to almost everything, they accept paint after curing, and they cost less upfront than silicone alternatives. For decades, that combination made them the obvious choice for specifiers and contractors.
The problem is that South Africa’s infrastructure environment is not the same as the temperate climates where polyurethane performs at its best. Moreover, the upfront cost advantage disappears quickly when maintenance and replacement cycles factor into the total calculation.
What UV Does to Polyurethane Joint Sealants
South Africa’s UV radiation levels rank among the highest in the world. The highveld in particular delivers intense solar radiation year round. Polyurethane sealants degrade under direct UV exposure through a process called photo-oxidation, where the organic polymer chain breaks down at the molecular level.
As a result, exposed polyurethane joint sealants yellow, chalk, lose flexibility and crack. Research shows this process begins within three years of installation in exposed environments. In South Africa’s highveld conditions, the timeline is shorter still.
Once a joint sealant cracks, it stops functioning as a seal. Water enters the joint, reaches the substrate below, and begins the cycle of subgrade erosion, concrete spalling and structural damage that makes joint failure so expensive to address.
The Movement Problem That Polyurethane Cannot Solve
South African infrastructure joints move constantly. Thermal cycling on the highveld drives daily temperature swings of 20 degrees or more between overnight lows and afternoon highs. Concrete expands and contracts with every cycle. Furthermore, heavy vehicle loading on roads, bridge decks and airport aprons adds dynamic movement that compounds the thermal stress.
Polyurethane sealants carry a movement rating of plus or minus 25% under ASTM C920. In moderate climates, that is adequate for most applications. In South Africa’s extreme thermal environment, joints on major infrastructure regularly exceed that movement range.
CSL 316, manufactured by CSL Silicones, carries a Class 50 rating under ASTM C920. That means it accommodates plus or minus 50% joint movement, double the capability of standard polyurethane products. Consequently, it handles the full range of thermal and dynamic movement that South African infrastructure joints experience without cohesive failure.
How Silicone Chemistry Solves What Polyurethane Cannot
Silicone sealants base their chemistry on the silicon oxygen polymer backbone rather than carbon based organic chemistry. That difference matters enormously in South Africa’s conditions.
The silicon oxygen bond does not respond to UV radiation the way organic polymers do. Therefore, a silicone joint sealant does not yellow, chalk, lose flexibility or crack under sustained sun exposure. Research confirms that silicone sealants carry satisfactory performance service lives exceeding 20 years in exposed exterior joints. Polyurethane sealants in the same conditions deliver five to eight years at best before replacement.
Moreover, silicone remains permanently flexible across the full temperature range South African infrastructure experiences. It does not become brittle in winter cold or soften under summer heat. As a result, it maintains its seal and its bond to the joint faces across thousands of thermal cycles that would fatigue and crack a polyurethane sealant.
Where CSL 316 Performs That Polyurethane Sealants Cannot
CSL 316 is a 100% silicone self levelling joint sealant formulated specifically for horizontal concrete expansion joints. It flows into the joint without tooling, bonds directly to concrete without primer in most applications, and cures at ambient temperature and humidity.
The applications where CSL 316 outperforms polyurethane most clearly are also the highest consequence environments in South African infrastructure.
On SANRAL roads and highways, joints move constantly under heavy freight loads and extreme thermal cycling. CSL 316 meets SANRAL specifications and COTO standard requirements. Polyurethane products at plus or minus 25% movement capacity are inadequate for the movement ranges that South African highway joints generate.
On airport aprons and taxiways, joints face jet fuel exposure, aircraft loading, and the constant thermal stress of tarmac surfaces in full sun. CSL 316 resists jet fuel and chemicals that would degrade polyurethane sealants. Furthermore, its service life reduces maintenance intervention on operational surfaces where every shutdown has a significant cost.
On harbour and port infrastructure, joints face salt water, chemical exposure and continuous heavy vehicle traffic. The chemical inertness of silicone means CSL 316 maintains its performance in environments that accelerate the degradation of organic sealant systems.
On industrial floors and logistics yards, forklift and heavy vehicle traffic generates constant dynamic loading on joints. CSL 316’s ultra high elongation and low modulus mean it recovers from that loading repeatedly without fatigue failure.
The Lifecycle Cost Argument
The upfront cost difference between polyurethane and silicone joint sealants is real. Silicone costs more per linear metre installed. However, the lifecycle cost calculation shifts dramatically when service life enters the equation.
A polyurethane joint sealant that needs replacement every five to seven years on a major highway or airport apron generates mobilisation costs, traffic management costs, joint preparation costs and material costs every replacement cycle. A silicone sealant that performs reliably for 20 or more years in the same application generates one set of those costs.
Furthermore, the consequential costs of joint failure matter greatly in infrastructure. Water ingress through failed road joints damages subgrade layers, creates pothole formation and accelerates the deterioration of the surrounding pavement structure. On bridge decks, water ingress through failed joints reaches reinforcing steel and begins the corrosion cycle that drives expensive structural repair. The cost of a failed joint sealant is never just the cost of the sealant itself.
CSL 316 Application Summary for South African Infrastructure
Substrate: concrete, steel and most construction substrates, clean dry and free of contamination. Joint width: 10mm to 50mm, depth to width ratio of 1 to 2. Application method: self levelling, flows without tooling in horizontal applications. System: single component, no mixing required. Cure: moisture cure RTV at ambient temperature and humidity. Movement capability: ASTM C920 Class 50, plus or minus 50% movement. Standards compliance: ASTM C920, ASTM D5893, COTO, SANRAL approved. Service environments: roads, bridges, airports, harbours, industrial floors, logistics yards. Chemical resistance: jet fuel, oils and mild chemicals.
Frequently Asked Questions
What is the best joint sealant for South African roads and infrastructure?
For horizontal concrete expansion joints on South African roads, bridges, airports and industrial floors, a 100% silicone self levelling sealant such as CSL 316 outperforms polyurethane alternatives in every critical performance category. Silicone carries double the movement capability of standard polyurethane products, does not degrade under UV exposure, and delivers a service life of 20 or more years compared to five to eight years for polyurethane in the same conditions.
Why does polyurethane joint sealant fail so quickly in South Africa?
South Africa’s UV radiation levels accelerate the photo-oxidation of polyurethane sealants significantly beyond what temperate climate data sheets reflect. Exposed polyurethane joint sealants yellow, chalk and crack under direct sun exposure, with failure occurring in under three years in high UV environments. South Africa’s extreme thermal cycling also pushes joints beyond the plus or minus 25% movement range that polyurethane products accommodate, causing cohesive failure in the sealant body.
Does CSL 316 meet SANRAL specifications?
Yes. CSL 316 complies with ASTM C920 Type M Grade P Class 50 and meets COTO standard specifications for SANRAL approved road projects. It accommodates plus or minus 50% joint movement, making it suitable for the movement ranges generated by South African highway and bridge infrastructure.
How long does a silicone joint sealant last compared to polyurethane?
In exposed exterior joints in South African conditions, silicone joint sealants such as CSL 316 carry service lives exceeding 20 years. Polyurethane sealants in the same conditions deliver satisfactory performance for five to eight years before UV degradation and movement fatigue require replacement. The lifecycle cost advantage of silicone becomes clear when replacement and mobilisation costs factor into the calculation.
Can CSL 316 handle jet fuel and chemical exposure on airport aprons?
Yes. CSL 316 resists jet fuel, oils and mild chemicals, making it suitable for airport apron and taxiway joints where polyurethane sealants would degrade under fuel exposure. It meets the movement and chemical resistance requirements of airport infrastructure applications and reduces maintenance intervention on operational surfaces.
What joint movement capability does CSL 316 provide?
CSL 316 carries an ASTM C920 Class 50 rating, meaning it accommodates plus or minus 50% movement of the joint width. This is double the plus or minus 25% movement capability of standard polyurethane joint sealants, and it reflects the actual movement ranges that South African infrastructure joints experience under thermal cycling and dynamic vehicle loading.
Is primer required when applying CSL 316 to concrete joints?
In most applications, no primer is necessary. CSL 316 bonds directly to clean, dry concrete without a primer. On highly porous substrates or in specific project conditions, a primer may be recommended. Joint surfaces must be clean, dry and free from dust, oil, grease, old sealant residue and loose concrete particles before application.
Conclusion
Polyurethane joint sealants remain the default choice on South African construction projects. However, the performance data tells a different story to the one that decades of market habit have established. UV degradation within three years, inadequate movement capability for South Africa’s thermal extremes, and lifecycle costs that compound with every replacement cycle make polyurethane the wrong choice for exposed infrastructure joints.
CSL 316 silicone joint sealant addresses the actual conditions that South African infrastructure joints face. Double the movement capability. Twenty year service life. UV stable. Chemically resistant. SANRAL and COTO compliant.
The question for every specifier and contractor is a simple one. Do you want to seal the joint once, or keep coming back to seal it again?
To find out more about CSL 316 for South African infrastructure joints, contact Technical Solutions Supplies.