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Concrete pavements face relentless movement. Thermal expansion, contraction, and heavy loads place extreme stress on joints, demanding a sealant engineered for more than just aesthetics. Dowsil 888 delivers the robust, flexible seal these demanding environments need, directly to concrete, without requiring a primer. It ensures joints remain protected against environmental degradation and differential movement, maintaining integrity over time.
Dowsil 888 Silicone Joint Sealant is a one-part, cold-applied, non-sag silicone material formulated specifically for Portland cement concrete pavement joints. It cures upon exposure to atmospheric moisture, forming a low-modulus silicone rubber designed to accommodate significant movement. This sealant supports new construction, repair, and remedial applications, even in joints that are not uniform in width or exhibit minor spalling, provided its movement capabilities are not exceeded.
Its remarkable movement capability of +100% extension and -50% compression means a 10mm joint can reliably expand by 10mm and compress by 5mm, ensuring joints remain sealed through severe thermal and structural shifts. The low modulus design minimises stress transfer to the bond line, enhancing durability in dynamic applications. Crucially, Dowsil 888 offers unprimed adhesion to Portland cement concrete, simplifying application and reducing installation time and material costs. It remains extrudable across a wide temperature range, from -29°C to 49°C, allowing for application in diverse Australian climates.
Dowsil 888 is supplied as a one-part, cold-applied, non-sag material, ready to use directly from its bulk container. This eliminates the need for mixing on site. Its workability allows dispensing into joints by hand or with an air-powered pump. Surface preparation is straightforward: surfaces must be clean, dry, and frost-free for optimal unprimed adhesion to concrete. The sealant typically achieves a skin-over in an hour or less under standard conditions. Proper joint design, including the correct placement of a compatible backer rod, like those from the Adheseal range, is critical to prevent three-sided adhesion and ensure sealant performance.
In concrete pavement joint systems, Dowsil 888 acts as the essential final seal. It is installed after the joint has been properly prepared and a backer rod inserted to control sealant depth and prevent three-sided adhesion. The sealant should be recessed below the pavement surface, with specific depths recommended to account for future grinding operations. This careful placement ensures long-term performance and protection of the concrete structure.
Yes, it is suitable for joints that are not uniform in width. Its low modulus and high movement capability of +100% extension and -50% compression help accommodate variations without failure.
No, a primer is not required for bonding to Portland cement concrete. For optimal adhesion, ensure the surface is clean, dry, and frost-free prior to application.
Do not use it for continuous water immersion, in totally confined spaces, or on asphalt pavements. Application is not recommended on wet or damp concrete, or during inclement weather.
The sealant can be extruded and applied across a wide temperature range, from -29°C to 49°C. This allows for use in various climate conditions.
| Application | Key benefit | Primary trades |
|---|---|---|
| New concrete pavement joints | Provides durable, flexible sealing with +100% extension / -50% compression movement capability, extending pavement life. | Pavement Contractors, Civil Engineers |
| Repair of existing concrete joints | Offers strong unprimed adhesion to Portland cement concrete, suitable for remedial work and joints with minor spalling. | Road Maintenance, Infrastructure Crews |
| Joints with irregular width | Accommodates variations in joint width due to its low modulus and high movement, maintaining a consistent seal. | Civil Engineers, Pavement Contractors |
| Exposed outdoor concrete structures | Delivers excellent weather and UV resistance, maintaining performance in harsh Australian conditions over time. | Infrastructure Contractors, Councils |
| Pavement requiring short-term fuel resistance | Provides resistance to incidental fuel exposure, supporting performance for airport runways and fuelling areas. | Airport Maintenance, Specialist Contractors |
Clean the joint thoroughly using wire brushing and high-pressure air. Remove all dust, laitance, curing compounds, and contaminants. Ensure the substrate is dry and frost-free before applying the sealant.
Allow concrete to cure properly. Saw-cut joints and remove dust with compressed air. Ensure the surface is free of all contaminants.
Grind and remove old sealant. Clean with abrasive method and air blowout. Ensure surface is recessed and uniform before installation.
Insert closed-cell backer rod to control sealant depth and prevent three-sided adhesion. Select appropriate diameter to allow compression during insertion.
Place backer rod to a depth that allows sealant thickness of 6–13 mm depending on joint width. Use joint width-to-depth ratio of approximately 2:1.
Account for expected grinding depth — place rod slightly deeper (up to 12.7 mm) so final profile sits correctly below the surface.
Dispense DOWSIL™ 888 using a manual, pneumatic, or bulk pump gun. Apply in a continuous motion to avoid air entrapment.
Cut nozzle to match joint width and extrude steadily. Tool immediately to avoid skin formation.
Use an air-powered system for large jobs. Maintain consistent pressure and flow rate above 72 mL/min.
Tool the sealant to form a concave profile recessed 9.5 to 12.7 mm below the slab surface. Protect from moisture for 8–24 hours. Clean tools using solvent or mechanical wiping before curing completes.
Allow 21 days at 25°C / 50% RH for full cure. Cooler temps will extend curing time.
Wipe uncured material using xylene or suitable solvent. Do not use water-based cleaners.
WARNING! Causes serious eye irritation. Harmful to aquatic life with long lasting effects.
Wear chemical goggles or face protection. Use chemical resistant gloves classified under AS/NZS 2161.10, such as Butyl rubber, Neoprene, Nitrile/butadiene rubber, EVAL, PVC, or Natural rubber. Wear appropriate protective clothing chemically resistant to this material. Respiratory protection (e.g., organic vapour cartridge) is recommended if exposure limits are exceeded or if irritation occurs.
Use local exhaust ventilation to maintain airborne levels below exposure limits. General ventilation is sufficient for most operations if no specific limits are exceeded.
Store in original, unopened containers below 32°C. Keep containers tightly closed and stored securely. Avoid storage with strong oxidizing agents. Dispose of product and empty containers in accordance with all local, state, and federal regulations at an approved waste disposal plant.
Proper surface preparation is crucial for a durable bond, preventing sealant failure and ensuring long-term performance.
Surface prep: The concrete surface must be clean, dry, and frost-free. Remove all dirt, dust, old sealant, and loose particles to ensure optimal adhesion.
Primer: Not required. DOWSIL™ 888 provides unprimed adhesion to Portland cement concrete.
| Property | Value |
|---|---|
| Color | Gray |
| Physical State | Paste |
| Slump | Pass (< 0.30 inches) |
| Extrusion Rate Minimum | 72 mL/min |
| Tack Free Time | Pass (5 hours max) |
| Heat Aging | 3.05% loss (max 10% loss) |
| Durometer Shore A-2 | 15 (max 25) |
| Specific Gravity | 1.48 |
| Cure Time 1/2"x1/2"x2" | 21 days at 25°C, 50% RH |
| Ultimate Elongation | >= 1000% (min 600%) |
| Tensile Stress @ 150% | 28 psi (max 45 psi) |
| Effects of Accelerated Weathering | Pass (5,000 hours) |
| Resilience | 77% (min 75%) |
| Joint Movement Capability | +100% / -50% (10 cycles) |
| Application Temperature Range | -29 to 49°C |
| Water Solubility | Insoluble |
| Flash Point Closed Cup | 100°C |
| Standards | ASTM D 5893 Type NS, FAA P-605, SS-S-200E Flame Test, EN 14187-5 Hydrolysis Test |
Here are some common examples on where Dowsil 888 Silicone Joint Sealant used by our customers.
