CSL 316 Self Levelling Silicone Joint Sealant: Frequently Asked Questions

What is CSL 316 and what is it used for?

CSL 316 is a single component self levelling silicone joint sealant manufactured by CSL Silicones. It seals horizontal concrete expansion joints on roads, bridges, airport aprons and taxiways, harbour and port infrastructure, industrial floors and logistics yards. It flows into the joint without tooling, bonds to concrete without primer in most applications, and cures at ambient temperature and humidity. Furthermore, it meets ASTM C920 Type M Grade P Class 50 and SANRAL specifications for South African road infrastructure projects. One correctly installed application delivers more than 20 years of waterproof joint performance where polyurethane sealants require replacement every five to seven years in the same conditions.

What is a concrete expansion joint and why does it need to be sealed?

A concrete expansion joint is an intentional gap designed into a concrete structure to allow the concrete to expand and contract with temperature changes, settle under load, and move without cracking. Without expansion joints, concrete roads, bridges, airport pavements and industrial floors would crack randomly and uncontrollably as the structure moves.

Sealing the joint is essential because an open joint allows water to penetrate into the subgrade beneath the pavement. Water in the subgrade erodes the supporting material, causes differential settlement, promotes concrete spalling at the joint faces, and in bridge structures reaches reinforcing steel and begins the corrosion cycle. Furthermore, debris entering an unsealed joint prevents the concrete from contracting freely, generating compressive stress that causes blowups in hot weather. A correctly installed joint sealant keeps water and debris out of the joint while accommodating the full movement range the joint is designed to handle.

What is the difference between silicone and polyurethane joint sealants?

The choice between silicone and polyurethane joint sealants determines how long the joint performs before it needs maintenance intervention. The chemistry of each material drives a set of performance differences that matter greatly on exposed infrastructure in Southern Africa’s climate.

UV stability is the most critical difference for outdoor infrastructure joints. Polyurethane is an organic carbon based polymer that degrades under UV radiation through photo-oxidation. The sealant yellows, loses flexibility, chalks and eventually cracks under sustained UV exposure. Research shows this process begins within three years in high UV environments. Silicone uses an inorganic silicon oxygen polymer backbone that does not respond to UV radiation. A silicone joint sealant does not yellow, chalk or crack regardless of UV exposure duration or intensity.

Movement capability is the second key difference. Standard polyurethane joint sealants carry an ASTM C920 Class 25 rating, meaning they accommodate plus or minus 25% movement of the joint width. CSL 316 carries a Class 50 rating, accommodating plus or minus 50% movement. On South African highway and bridge joints where thermal cycling generates movement ranges that regularly exceed the polyurethane limit, this difference determines whether the sealant holds or fails cohesively.

Service life is the practical outcome of these differences. Polyurethane joint sealants in exposed outdoor infrastructure in Southern Africa typically require replacement every five to seven years. CSL 316 silicone joint sealant provides a service life exceeding 20 years in the same conditions. Over a 20 year asset life, the lifecycle cost advantage of silicone is substantial when all replacement, mobilisation and traffic management costs factor into the calculation.

What does ASTM C920 Class 50 mean?

ASTM C920 is the American Society for Testing and Materials standard specification for elastomeric joint sealants. It defines the performance requirements for sealants used in construction joints and is the primary international standard referenced in infrastructure joint sealant specifications globally.

The Class designation in ASTM C920 defines the movement capability of the sealant. Class 25 means the sealant accommodates plus or minus 25% movement of the installed joint width. Class 50 means it accommodates plus or minus 50% movement. Class 50 is the highest movement capability classification in the standard and reflects a sealant that handles twice the movement of a standard Class 25 polyurethane product.

The Type M designation means the sealant is suitable for use with mortar, meaning concrete and masonry substrates. The Grade P designation means it is a pourable self levelling product, suitable for horizontal joint applications where the sealant flows into the joint under gravity rather than requiring tooling to shape the profile.

CSL 316 meets ASTM C920 Type M Grade P Class 50, which means it is the highest movement rated self levelling sealant classification under the standard. This is the specification required for SANRAL highway and bridge projects in South Africa and for major airport and infrastructure projects globally.

Does CSL 316 meet SANRAL specifications?

Yes. CSL 316 complies with SANRAL and COTO standard specifications for concrete joint sealants on South African national road infrastructure projects. It meets the ASTM C920 Type M Grade P Class 50 specification that SANRAL references for highway concrete pavement joints, and it meets the movement capability and chemical resistance requirements of COTO standards for road and bridge joint sealants. Contractors and specifiers on SANRAL approved projects can specify CSL 316 with confidence that it meets the relevant technical standards for the application.

Why does polyurethane joint sealant fail so quickly in South Africa?

Polyurethane joint sealants fail faster in South Africa than temperate climate data sheets predict for two compounding reasons.

South Africa has some of the highest UV radiation levels in the world. The highveld in particular delivers intense solar radiation year round. Photo-oxidation of the polyurethane resin begins within the first years of service in direct sun exposure on road and bridge joints. The sealant loses flexibility, cracks across its body, and stops functioning as a waterproof joint seal. Water then enters the joint and the subgrade damage that follows generates the pothole formation and pavement deterioration that is visible on road networks across the country.

South Africa’s thermal cycling compounds the UV degradation. The daily temperature swing on the highveld between overnight lows and afternoon highs can exceed 20 degrees Celsius. That cycle drives joint movement that pushes standard Class 25 polyurethane sealants beyond their movement capability, causing cohesive failure in the sealant body. CSL 316 accommodates double the movement range of Class 25 polyurethane and maintains its flexibility under UV exposure, eliminating both failure mechanisms simultaneously.

What is self levelling and why does it matter for horizontal joints?

Self levelling means the sealant has a low enough viscosity to flow under gravity when applied to a horizontal joint, spreading across the joint width and filling the joint profile without requiring a tool to push and shape the material. This is a critical property for horizontal concrete expansion joints on roads, bridge decks, airport aprons and industrial floors.

Non-sag sealants, which are formulated for vertical and overhead joints, are too viscous to flow into horizontal joints properly. They trap air pockets, leave voids in the joint profile, and do not bond uniformly to the joint faces. Self levelling sealants fill horizontal joints completely, bond to the full joint face area, and produce a smooth flush surface that does not create a trip hazard for vehicle tyres or pedestrian traffic. CSL 316 is a self levelling formulation specifically engineered for horizontal joint applications in road and infrastructure paving.

What is the correct joint preparation before applying CSL 316?

Correct joint preparation is critical for long term sealant performance. The joint faces must be clean, dry and free from all contamination including dust, dirt, grease, oil, old sealant material, laitance and loose concrete particles. All of this material prevents the sealant from bonding to the concrete and is the primary cause of adhesion failure on joint sealant installations.

The joint width to depth ratio must also be correct. A depth to width ratio of 1 to 2 is recommended for most applications, meaning the sealant depth should be approximately half the joint width. This ratio ensures the sealant deforms in extension and compression rather than in shear, which is the correct deformation mode for maximum service life. A backer rod of closed cell polyethylene foam should be installed to the correct depth before sealant application to control the sealant depth and prevent three-sided adhesion, which restricts the movement the sealant can accommodate.

On most clean, dry concrete surfaces, no primer is required before applying CSL 316. On highly porous substrates or specific project conditions, a primer may be recommended. Contact Technical Solutions Supplies for substrate specific application guidance.

What is a backer rod and why is it needed?

A backer rod is a compressible closed cell polyethylene foam rod inserted into the joint before sealant application. It serves two purposes. First, it controls the depth of the sealant in the joint, ensuring the correct depth to width ratio is maintained across the full joint length. Second, it acts as a bond breaker at the base of the joint, preventing the sealant from bonding to three surfaces simultaneously. Three-sided adhesion restricts the movement the sealant can accommodate and causes premature cohesive failure when the joint moves. With a backer rod installed correctly, the sealant bonds only to the two opposing joint faces and deforms correctly in extension and compression as the joint moves.

Can CSL 316 handle heavy vehicle traffic on roads and industrial floors?

Yes. CSL 316 is specifically formulated for horizontal joint applications that carry vehicle traffic. Its ultra high elongation and low modulus silicone chemistry allows it to deform repeatedly under dynamic loading from vehicles crossing the joint without fatigue failure. Conventional polyurethane sealants stiffen over time as UV degradation and thermal cycling reduce their flexibility, increasing the stress transferred to the bond line at the joint face and eventually causing adhesion failure or cohesive tearing under traffic loading. CSL 316 maintains its flexibility and elastic recovery throughout its service life, accommodating continuous traffic loading on highway joints, airport apron joints and heavy industrial floor joints without the progressive hardening that causes polyurethane sealants to fail under traffic.

Does CSL 316 resist jet fuel and chemicals?

Yes. CSL 316 resists jet fuel, aviation fuels, oils, hydraulic fluids and mild chemicals. This chemical resistance makes it suitable for airport apron and taxiway joints where polyurethane sealants degrade under fuel exposure. It also makes it appropriate for industrial floor joints in facilities handling fuel, oil and chemical spillage. The silicone chemistry of CSL 316 is chemically inert to the range of fuels and mild chemicals encountered in airport and industrial floor environments. Contact Technical Solutions Supplies for guidance on specific chemical resistance requirements for your application.

Is CSL 316 suitable for bridge deck joints?

Yes. Bridge deck joints represent one of the most demanding joint sealant applications in infrastructure. They face continuous dynamic loading from vehicle traffic, the full range of thermal movement generated by the bridge structure and the deck pavement, exposure to rain, salt and contamination from road drainage, and in coastal environments the additional challenge of marine salt aerosol.

CSL 316’s Class 50 movement rating handles the full thermal and dynamic movement range that South African bridge deck joints generate. Its permanently flexible silicone chemistry accommodates the structural movement of the bridge without cohesive failure. Its UV stability means it does not degrade on exposed joint faces between the carriageway surface and the edge beam. Its chemical resistance prevents degradation from road surface runoff and de-icing chemicals where applicable. These properties combined make CSL 316 the appropriate specification for bridge deck expansion joints on South African national road infrastructure.

Is CSL 316 suitable for airport apron and taxiway joints?

Yes. Airport apron and taxiway joints face a unique combination of demands that eliminate most conventional joint sealants from consideration. Jet fuel spillage is the most significant challenge. Polyurethane sealants swell and degrade under sustained fuel exposure, losing their waterproofing integrity and eventually requiring emergency maintenance on operational surfaces. CSL 316 resists jet fuel and aviation fuels without swelling or degrading.

Aircraft loading on apron joints is also substantially higher than road vehicle loading. The static and dynamic loads from wide body aircraft on taxiway joints generate movement and compressive stress that requires a high movement, high recovery sealant. CSL 316’s Class 50 movement rating and its elastic recovery characteristics after compression make it suitable for the loading conditions on airport pavement joints. Furthermore, its 20 year plus service life reduces maintenance intervention on operational surfaces where every shutdown has a significant cost in terms of flight delays and airport operations.

Is CSL 316 suitable for harbour and port infrastructure?

Yes. Harbour and port infrastructure combines salt water exposure, heavy vehicle traffic from container handling equipment, chemical contamination from cargo operations, and continuous wetting and drying cycles that accelerate the degradation of organic sealant systems. CSL 316’s silicone chemistry resists chloride attack and does not hydrolyse in the marine environment. Its chemical inertness resists the range of chemical contaminants found in port operations. Its Class 50 movement rating accommodates the thermal and dynamic movement generated by heavy container handling equipment crossing concrete pavement joints. Consequently, CSL 316 is the appropriate joint sealant specification for concrete paving joints in South African harbour and port facilities including the Port of Durban, Port of Cape Town and Richards Bay Coal Terminal environments.

Is CSL 316 suitable for water infrastructure including dams, reservoirs and canals?

Yes. Water infrastructure joints including dam faces, reservoir walls, canal linings and water treatment facility concrete joints require a sealant that maintains its waterproofing integrity under continuous water contact and the thermal and structural movement that water retaining structures experience. CSL 316 does not absorb water or degrade under continuous water immersion, making it suitable for horizontal and near horizontal joint applications in water infrastructure. Contact Technical Solutions Supplies for specific guidance on vertical joint applications in water infrastructure, as a non-sag sealant formulation may be more appropriate for some of these applications.

How does thermal cycling affect joint sealants on South African roads?

Thermal cycling is one of the primary causes of joint sealant failure on South African road infrastructure. The highveld experiences daily temperature swings of 20 degrees Celsius or more between overnight lows and afternoon highs. Seasonal extremes extend this range further, with Gauteng recording summer afternoon temperatures above 35 degrees Celsius and winter overnight temperatures below 5 degrees Celsius.

Concrete expands and contracts with every temperature cycle. On a 10 metre concrete pavement slab, a 30 degree temperature change generates approximately 3 millimetres of movement at each joint. Over the course of a year, that joint opens and closes hundreds of times. Standard polyurethane sealants with a Class 25 movement rating are at their movement limit on standard highway joint spacings in South Africa’s thermal environment. CSL 316 at Class 50 provides double the movement margin, ensuring the sealant accommodates the full thermal movement range without reaching its cohesive strength limit.

What is the lifecycle cost advantage of CSL 316 compared to polyurethane sealants?

The direct material cost of CSL 316 is higher than standard polyurethane joint sealant. However, the lifecycle cost comparison over a 20 year infrastructure asset life tells a fundamentally different story.

A polyurethane joint sealant that fails within five to seven years generates a full replacement cycle including traffic management and road closure costs, joint cleaning and preparation costs, material and application labour costs, and the consequential costs of any subgrade damage caused by water ingress through the failed sealant in the period between failure and replacement. On a major highway with thousands of linear metres of expansion joints, these costs are substantial and they repeat every five to seven years.

CSL 316 applied correctly at the outset generates one set of those costs across a 20 year period. Research on silicone versus polyurethane joint sealant lifecycle costs consistently shows silicone delivering 40 to 50 percent lower total cost of ownership over 20 years when all maintenance and consequential costs are included. For SANRAL and provincial road authorities managing large joint sealant programmes across the national road network, the lifecycle cost advantage of specifying CSL 316 from the outset is significant at programme scale.

How long does CSL 316 take to cure?

CSL 316 is a moisture cure RTV silicone sealant. It cures by reacting with atmospheric moisture rather than by solvent evaporation or chemical mixing. The curing process proceeds at ambient temperature and humidity. The sealant becomes tack free at the surface within approximately two hours under ambient conditions. Full depth cure develops progressively from the surface downward over 7 to 14 days depending on the joint width, depth, temperature and ambient humidity. Traffic can generally be permitted over the joint once the surface has cured sufficiently to resist deformation, typically within 24 hours under normal ambient conditions. Contact Technical Solutions Supplies for specific cure time guidance for your project conditions.

Does CSL 316 require a primer?

In most applications on clean, dry concrete, no primer is required. CSL 316 bonds directly to concrete without a primer under correct surface preparation conditions. On highly porous substrates, contaminated surfaces or specific project conditions, a primer may be recommended to improve adhesion. The joint faces must be clean, dry and free from contamination before application regardless of whether a primer is used. Contact Technical Solutions Supplies for substrate specific primer guidance before starting your project.

What temperature range does CSL 316 perform in?

CSL 316 remains flexible and maintains its joint sealing performance from minus 40 degrees Celsius to plus 150 degrees Celsius. This temperature range covers every climate condition encountered across Southern Africa, from frost conditions on the Drakensberg and Lesotho highlands to extreme summer heat on industrial floors in the Northern Cape. The permanent flexibility of silicone across this range means CSL 316 does not become brittle in cold conditions or soft in extreme heat, both of which cause polyurethane sealants to fail at the extremes of South Africa’s climate range.

Can CSL 316 be applied over an existing failed polyurethane sealant?

No. Existing failed sealant material must be fully removed from the joint before applying CSL 316. Old sealant residue on the joint faces prevents CSL 316 from bonding directly to the concrete substrate, and any adhesion failure in the old sealant system will transfer through to the new installation. Joint faces must be cleaned back to sound, clean concrete before applying the new sealant. This preparation step is critical for long term performance and should not be shortcut regardless of the condition of the existing sealant.

What standards does CSL 316 comply with?

CSL 316 complies with ASTM C920 Type M Grade P Class 50, which is the primary international standard for elastomeric joint sealants in infrastructure applications. It also meets ASTM D5893, the standard specification for cold applied single component silicone joint sealants for portland cement concrete pavements, which is the standard specifically developed for road and airfield pavement joint sealants. Furthermore, it meets COTO standard specifications and SANRAL requirements for joint sealants on South African national road infrastructure projects.

Is CSL 316 suitable for parking structure joints?

Yes. Multi storey parking structures present demanding joint conditions including vehicle traffic, exposure to rain and water runoff, thermal cycling on exposed upper deck levels, and in coastal locations salt contamination from vehicles and the marine environment. CSL 316 accommodates the movement and traffic loading of parking structure joints while maintaining its waterproofing performance across the full service life. Protecting parking structure joints from water ingress is critical for the long term durability of the reinforced concrete structure, as water reaching the reinforcing steel initiates the corrosion and concrete spalling cycle that is the primary cause of structural deterioration in ageing multi storey car parks.

Where is CSL 316 available?

CSL 316 is manufactured by CSL Silicones and distributed exclusively across Sub-Saharan Africa by Technical Solutions Supplies. We supply throughout South Africa, Namibia, Botswana, Zimbabwe, Zambia, Mozambique, Tanzania, Kenya, Uganda, Rwanda, Angola, the Democratic Republic of Congo, Malawi, Madagascar, Mauritius, Eswatini and Lesotho.

We cover the full spectrum of infrastructure joint sealant applications across the continent, from SANRAL national highway projects and major airport developments to harbour infrastructure, mining facility paving, water infrastructure and industrial floor applications across Southern and Eastern Africa. We provide technical specifications, application guidance, product samples, contractor training and on site technical support for joint sealant projects of all sizes across the region.

Who should I contact for a technical specification or project quote?

Contact Technical Solutions Supplies directly for project specific technical guidance, joint sealant specification and pricing.

Phone: 031 002 7376 Email: sales@tssupplies.co.za

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