Polyurethane is the default joint sealant in South Africa. Contractors specify it on roads, bridges, airport aprons and industrial floors almost without thinking. However, its record as a joint sealant in South Africa tells a different story from the one on the data sheet. Strong UV and wide temperature swings age it faster than in milder climates, and the result is cracked joints, water in the structure below, and maintenance that never seems to end.
Why Polyurethane Became the Default Joint Sealant in South Africa
Polyurethane became the default on local projects for simple reasons. It bonds to almost everything, it can be painted after curing, and it costs less upfront than silicone. For decades, that made it the obvious choice for specifiers and contractors.
The problem is that South African infrastructure is not a temperate European site. Also, the upfront saving disappears quickly once maintenance and replacement cycles enter the sums.
What UV Does to Polyurethane
Our UV levels rank among the highest in the world, and the Highveld gets intense sun all year. Polyurethane breaks down under UV through photo oxidation, where the organic polymer chain degrades at the molecular level.
As a result, an exposed polyurethane joint sealant in South Africa yellows, chalks, loses flexibility and cracks. In full sun on the Highveld, that can start within a few years of installation.
Once a joint sealant cracks, it stops sealing. Water then enters the joint, reaches the layers below, and starts the cycle of subgrade erosion, spalling and structural damage that makes joint failure so expensive.
The Movement Problem Polyurethane Cannot Solve
Infrastructure joints move all the time. On the Highveld, daily swings of 20°C or more between night and afternoon are normal, and concrete expands and contracts with every cycle. In addition, heavy vehicles on roads, bridge decks and aprons add dynamic movement on top of the thermal stress.
Most polyurethane products carry a Class 25 rating, which means ±25% of the joint width. In mild climates that is often enough. On major infrastructure in South Africa, however, joints regularly move more than a Class 25 joint sealant can handle.
CSL 316, made by CSL Silicones, is rated for +100/−50% movement per ASTM C719. In other words, it can stretch to twice its installed width and compress to half of it. That is four times the extension and twice the compression of a Class 25 sealant.
How Silicone Solves What Polyurethane Cannot
Silicone sealants are built on a silicon oxygen backbone, not on carbon based organic chemistry. That difference matters a great deal in our conditions.
The silicon oxygen bond does not break down under UV the way organic polymers do. CSL states that 316 is unaffected by sunlight, ozone, rain and temperature extremes, and the TDS records no degradation in accelerated weathering to ASTM C793. By comparison, polyurethane in the same exposure typically lasts five to eight years before it needs replacing.
Silicone also stays flexible across the full temperature range our infrastructure sees. CSL 316 keeps its properties from −60°C to 200°C, so it does not go brittle in winter or soft in summer. That is why silicone is the better joint sealant for South Africa, because it keeps its seal through thousands of cycles that would fatigue and crack polyurethane.
The Right Joint Sealant for Roads, Airports and Ports in South Africa
CSL 316 is a 100% silicone self levelling sealant made for horizontal concrete joints. It flows level into the joint, bonds to clean concrete and steel without primer, and cures at ambient temperature and humidity. The applications where it beats polyurethane most clearly are also the highest risk ones.
Roads and highways
Road joints move constantly under freight loads and thermal cycling. CSL 316 complies with ASTM D5893 Type SL and conforms to the COTO specification used on SANRAL projects. A ±25% polyurethane, by contrast, often cannot keep up with highway joint movement.
Airport aprons and taxiways
Apron joints face fuel spills, aircraft loads and full sun on the concrete. CSL 316 has been tested against jet fuel, hydraulic fluid and deicing fluid, which degrade polyurethane. Because it lasts longer, it also means fewer shutdowns on operational surfaces. Read more on silicone sealant for airport aprons.
Harbours and ports
Port joints face salt water, cargo spills and heavy container handlers. Silicone does not break down in salt air or chlorides, so CSL 316 keeps performing where organic sealants age fast. See our article on joint sealants for harbours.
Industrial yards and logistics areas
Trucks and container handlers load external yard joints all day. CSL 316 has 1000% elongation and a low modulus, so it recovers from that loading again and again. For more, read about joint sealant for heavy traffic.
The Lifecycle Cost of a Joint Sealant in South Africa
The upfront price gap between polyurethane and silicone is real, because silicone costs more per metre installed. However, the sums change once service life enters the picture.
Across South Africa, a polyurethane joint sealant that needs replacing every five to seven years on a highway or apron brings mobilisation, traffic management, joint preparation and material costs every time. By contrast, CSL reports 316 joints in service in North America for more than 20 years, which means paying those costs once.
The knock on costs matter too. Water through failed road joints damages the subgrade and causes potholes. On bridge decks, water reaches the reinforcing steel and starts corrosion that ends in structural repair. In short, a failed joint never costs only the sealant. Read more on the hidden cost of joint failure.
CSL 316 Application Summary
- Substrate: concrete and steel, clean, dry and free of dust, oil and old sealant
- Joint faces: sandblast the top 25 mm of each face, then blow out with oil free air
- Joint width: 6 to 25 mm, sealant thickness half the joint width
- Application: one part, no mixing, fill from the bottom up, then tool against the joint faces
- Cure: tack free 90 minutes, cured 48 hours, full properties 7 days
- Movement: +100/−50% per ASTM C719
- Standards: ASTM D5893 Type SL, conforms to the COTO specification used on SANRAL projects
- Uses: roads, bridges, airports, harbours, industrial yards
Joint Sealant South Africa: Frequently Asked Questions
What is the best joint sealant in South Africa for roads and infrastructure?
For horizontal concrete joints on roads, bridges, airports and yards, the best joint sealant in South Africa is a 100% silicone self levelling product such as CSL 316. It outperforms polyurethane on movement, UV resistance and service life, and it is rated +100/−50% against ±25% for a typical polyurethane.
Why does polyurethane fail so quickly here?
There are two reasons a polyurethane joint sealant fails early in South Africa. First, strong UV breaks it down faster than temperate climate data sheets suggest, so it yellows, chalks and cracks. Second, wide temperature swings push joints past the ±25% that most polyurethanes can handle, so the sealant tears.
Does CSL 316 meet SANRAL requirements?
SANRAL does not approve individual products. Instead, it refers specifiers to the COTO specifications. CSL 316 conforms to the COTO specification used on SANRAL projects and complies with ASTM D5893 Type SL.
How long does silicone last compared to polyurethane?
Polyurethane on exposed joints typically lasts five to eight years. For silicone, CSL reports 316 joints in service in North America for more than 20 years. Actual life depends on movement, exposure, traffic and installation.
Can CSL 316 handle jet fuel on airport aprons?
Yes. CSL 316 has been tested against jet fuel, hydraulic fluid and deicing fluid without losing adhesion or cohesion. The test reports are on the CSL 316 product page.
Does CSL 316 need a primer?
No. CSL 316 bonds to clean, dry concrete and steel without primer. The joint faces must still be sandblasted and free of dust, oil and old sealant. More answers are in the CSL 316 FAQ.
Conclusion
Polyurethane is still the default joint sealant in South Africa, but habit is not performance. UV damage, too little movement capability for our temperature swings, and repeat replacement costs make it the wrong choice for exposed infrastructure joints.
CSL 316 is built for the conditions our joints actually face. It is rated +100/−50%, resists UV and fuel, and conforms to the COTO specification used on SANRAL projects. For a wider comparison that includes hybrids, read our article on concrete joint sealant types.
So the question for every specifier and contractor is simple. Do you want to seal the joint once, or keep coming back to seal it again? Contact Technical Solution Supplies to discuss your project.
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