Not sure on how much sealant you'll need? Use our calculator to find out.
For Portland cement concrete pavement joints in new construction or remedial roadworks, Dowsil 888 Silicone Joint Sealant provides a high-movement, unprimed barrier against water and debris. Formulated specifically for concrete-to-concrete joints, this low-modulus, non-sag silicone accommodates highly irregular joint widths and bridges minor concrete spalling along the joint edges without requiring a primer.
Dowsil 888 is a one-part, cold-applied silicone that cures on exposure to atmospheric moisture to form a flexible silicone rubber. Because concrete pavements undergo extreme thermal expansion and contraction, the sealant is formulated with ultra-low modulus properties, allowing +100% extension and -50% compression. This extreme flexibility reduces the stress on the concrete bond line, preventing adhesive or cohesive failure when the slabs contract in cold weather. It bonds directly to clean, dry, and frost-free Portland cement concrete without a primer, and resists short-term exposure to road fuels.
To prevent three-sided adhesion and control sealant depth, a proper backer rod must be installed. The sealant must be recessed a minimum of 3/8 inch to 1/2 inch (9.53 mm to 12.7 mm) below the pavement surface—or deeper if road grinding is planned—to protect the joint from traffic damage. For standard applications, follow these joint dimensions:
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.
