JOINT SEALANTS
CSL 316 is a one part self levelling silicone sealant for horizontal concrete joints, made by CSL Silicones. Contractors use it on roads, bridges, airport aprons and taxiways, harbours, industrial floors and logistics yards. Because it flows level into the joint, it gives a smooth finish, and it cures at ambient temperature and humidity.
On standards, it complies with ASTM D5893 Type SL, the specification for silicone joint sealants in concrete pavements. Per ASTM C719, it is also rated for +100/−50% joint movement. In addition, it conforms to the COTO specification used on SANRAL projects. Finally, CSL reports 316 joints in service in North America for more than 20 years, and backs the sealant with a 10 year product warranty.
Why Polyurethane Joint Sealants Keep Failing on South African Infrastructure
Polyurethane joint sealants dominate the South African market because they cost less upfront and bond to most substrates. For decades that made them the default on roads, bridges, airports and industrial floors. However, their record in local conditions is less convincing.
South Africa has some of the highest UV levels in the world. Polyurethane is an organic polymer, and UV breaks it down through photo oxidation. As a result, the sealant hardens, chalks and cracks over time. Once a joint sealant cracks, it stops sealing. Water then reaches the subgrade and starts the erosion that leads to potholes and pavement failure.
Thermal cycling also adds to the damage. On the Highveld, the gap between overnight lows and afternoon highs is often more than 20°C. So the slabs move every day, and a standard Class 25 polyurethane, rated for ±25% movement, is pushed past its limit and tears.
A failed joint never costs only the sealant. On roads, water through failed joints weakens the subgrade. On bridges, water through deck joints reaches the reinforcing steel and starts corrosion, as our article on bridge corrosion protection explains.
CSL 316 deals with both causes. First, silicone resists UV far better than polyurethane, and the TDS records no degradation in accelerated weathering to ASTM C793. Second, its +100/−50% movement rating gives four times the extension and twice the compression of a Class 25 sealant.
Self Levelling Silicone Sealant Properties
Movement. Rated +100/−50% per ASTM C719. So the sealant can stretch to twice its installed width and compress to half of it without failing. As a result, it covers the thermal and traffic movement in highway, bridge and airport joints.
UV resistance. CSL states that 316 resists sunlight, ozone, rain, snow and temperature extremes. That is because the silicon oxygen backbone does not break down under UV the way polyurethane does.
Self levelling. The sealant flows under its own weight to a smooth, level surface across the joint. Then tool it against the joint faces for the best adhesion.
Flexibility. Elongation at break is 1000% and hardness is 10 Shore A. As a result, the low modulus puts very little stress on the joint faces as the slabs move.
Temperature range. The cured sealant also keeps its properties from −60°C to 200°C.
Fuel resistance. CSL tested 316 using a modified ASTM C719 cycle, with seven days of exposure to JP-4 jet fuel, Skydrol B hydraulic fluid, other hydraulic fluid and a 50:50 glycol and water mix. Therefore it suits airport aprons, fuel handling areas and port pavements. The test summary is in the documents below.
Neutral cure. 316 uses an oxime cure, so it releases no acetic acid as it cures.
Primer. No primer is needed on most substrates. Still, run a trial bead on the actual concrete and check adhesion after 7 days. If it falls short, we will advise on a primer with CSL.
Where This Self Levelling Silicone Sealant Is Used
Roads and highways. National and provincial roads carry thousands of metres of concrete joints. 316 also conforms to the COTO specification used on SANRAL projects and handles the movement from daily temperature swings and heavy freight. For example, a supplier to the Texas Department of Transportation ordered three truckloads of 316, about 124,800 cartridges, in 2021 for highway joints. The case history is in the documents below.
Bridge decks. Deck joints take traffic loading, thermal movement of the structure, and water and salt from road drainage. So the high movement rating and low modulus suit these joints well.
Airports. Aprons and taxiways see fuel spills, aircraft loads and full sun on the concrete. Because 316 keeps its seal after jet fuel exposure, it cuts the number of shutdowns for joint repair.
Harbours and ports. Port pavements face salt air, heavy container handlers and constant wetting and drying. However, silicone does not break down in salt air or chlorides.
Industrial floors and logistics yards. Forklifts and trucks load the joints thousands of times a day. Even so, the low modulus lets 316 recover from that movement again and again.
Water infrastructure. For joints that get wet, such as canal linings and reservoir decks, 316 stays flexible and keeps its seal. However, for joints that are permanently under water, or in contact with drinking water, contact us before specifying.
Application Summary
- Substrate: concrete and steel, clean, dry and free of dust, frost, oil and old sealant
- Joint faces: first sandblast the top 25 mm of each face, then blow out with oil free compressed air in one direction
- New concrete: allow at least 7 days to cure and dry before sealing
- Joint width: 6 to 25 mm
- Sealant thickness: about half the joint width, 6 to 12 mm, recessed 6 to 12 mm below the surface
- Backer rod: polyurethane or expanded polyethylene foam, a snug fit on both sides, because it sets the depth and prevents three sided adhesion
- Application: one part, so no mixing. First fill from the bottom up in one continuous pass, then tool against the joint faces
- Application temperature: ambient up to 50°C. For colder conditions, however, check with us first
- Cure at 25°C and 50% humidity: tooling time 22 minutes, tack free 90 minutes, cured 48 hours, full properties 7 days
- Traffic: a properly recessed joint can take traffic after installation and clean up are complete
- Standards: ASTM D5893 Type SL, movement +100/−50% per ASTM C719, conforms to the COTO specification used on SANRAL projects
- Colour: grey, and custom colours are also available
- Packaging: 300 ml cartridges, 18.9 L pails, 189 L drums
Self Levelling Silicone Sealant vs Polyurethane
Standard polyurethane joint sealants are typically rated Class 25, or ±25% movement. They also break down under South African UV, so on exposed infrastructure they need replacing far sooner than silicone.
CSL 316, by contrast, is rated +100/−50% per ASTM C719, resists UV according to CSL, keeps its seal after jet fuel exposure, and has a service record of more than 20 years in North America. In addition, CSL offers a 10 year product warranty against material defects, on its standard terms.
Technical Solution Supplies distributes CSL Silicones products across Southern Africa, including the DRC and the Seychelles. For full technical data, see the CSL 316 FAQ, download the documents below, or contact us.
Joint Sealant Technical Documents
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Proud exclusive distributor of CSL Silicones in Southern Africa.
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