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DOWSIL™ 888 Silicone Joint Sealant: A Technical Overview
DOWSIL™ 888 is a non-sag, cold-applied silicone joint sealant purpose-built for Portland cement concrete pavements. Its one-part formula is moisture-curing, permanently flexible, and capable of 100% extension and 50% compression. Designed for Australia’s climate extremes and high-traffic exposure, it adheres without primer on clean concrete, resists UV and short-term fuel exposure, and cures to a low-modulus elastomer. Suitable for both new construction and remedial joints, including irregular widths or minor spalling, it is ideal for airport tarmacs, roadways, industrial loading bays, and service stations.
100%
Elongation Movement Capability
Core Features & Specifications
- One-part, cold-applied silicone — ready-to-use with no mixing
- Joint movement capability: +100% extension / -50% compression
- Low modulus formulation — Shore A hardness of 15
- Skin-over time: ≤ 1 hour; Full cure: 21 days @ 25°C / 50% RH
- Unprimed adhesion to Portland cement concrete
- Ultimate elongation ≥ 1000%; Tensile stress at 150%: 28 psi
- Passes ASTM C719 (cyclic movement test), ASTM C792, C793
- Resilience: 77%; Specific gravity: 1.48
- Extrusion rate ≥ 72 mL/min; Non-sag slump < 0.30 inches
- Application temp range: -20°C to +49°C
- Recess joint 3/8" to 1/2" below surface; use backer rod to avoid 3-sided adhesion
- Short-term fuel resistant; UV and weather resistant
- Pack sizes: 857 mL cartridge, 17 L pail, 189 L drum
- Complies with ASTM D5893, FAA P-605, SS-S-200E, EN 14187-5
The DOWSIL™ 888 Advantage
- Withstands extreme expansion and contraction in road joints
- Saves time with unprimed adhesion on concrete
- Long-term performance in exposed and fuel-exposed zones
- Compliant with major international pavement sealant standards
- Suitable for grind-back and post-finish applications
- Prevents edge cracking and moisture ingress in rigid slabs
Best Practices: Do's & Don'ts
Do
- Use backer rod to control joint depth and avoid 3-sided adhesion
- Recess sealant 9–12 mm below pavement surface
- Apply to clean, dry, frost-free Portland cement concrete
Don't
- Don't apply in standing water or on damp surfaces
- Don't use on asphalt substrates or in continuous water immersion
- Don't exceed movement capability (+100% / -50%) during design
Applications in Practice: Trade Scenarios
For Civil Contractors (On-Site Applicator): Road Joint Sealing
The Engineering Challenge
Concrete pavements in Australian road networks expand and contract due to high daily thermal cycling. Sealants must absorb this movement without cracking, debonding or allowing moisture ingress into slab joints.
The System-Based Solution with DOWSIL™ 888
Install DOWSIL™ 888 in joints 6–25 mm wide using backer rod and a 3/8" to 1/2" recess below surface. Sealant accommodates +100% expansion and -50% compression with no failure. Use in new pours or rehab joints post-grind.
Best Practice Note
Avoid three-sided adhesion — always install backer rod. Clean joint surfaces with compressed air and wire brushing before application. Ensure ambient temp ≥10°C and avoid rain during curing.
For Airport Maintenance Crews (Specifier): Apron and Taxiway Sealant
The Engineering Challenge
Aprons and taxiways demand flexible, UV-stable sealants that can handle joint irregularities, vibration, and potential fuel spills. Many fail from cohesive cracking or lose bond prematurely.
The System-Based Solution with DOWSIL™ 888
DOWSIL™ 888 complies with FAA P-605 and SS-S-200E standards and withstands jet fuel splash. Its low modulus formulation and 1000% elongation prevent cracking under airside joint movement.
Best Practice Note
Use proper personal protection for fuel-exposed areas. Mask edges to control sealant width and recess depth before backfilling to spec. Conduct adhesion testing on aged concrete as needed.
Performance Benchmark: DOWSIL™ 888 vs. Standard Alternatives
| Metric | DOWSIL™ 888 | Standard PU Sealant | Advantage |
|---|---|---|---|
| Movement Capability | +100% / -50% Excellent | ±25% | 4× greater movement performance |
| Fuel Resistance | Short-term splash resistant | Limited or none | Safer for forecourts & aprons |
| UV Resistance | Pass 5,000 hrs | Moderate | Better for exposed pavements |
| Application Temp | -20°C to +49°C | +5°C to +35°C | Broader jobsite usability |
Frequently Asked Questions
What is the movement capability of DOWSIL™ 888 Silicone Joint Sealant?
DOWSIL™ 888 offers a high movement capability of +100% extension and -50% compression, making it ideal for concrete joints subjected to significant thermal and structural movement. This performance ensures long-term durability in applications like roads, runways, and carparks.
Can DOWSIL™ 888 be applied without a primer on concrete?
Yes. DOWSIL™ 888 provides excellent unprimed adhesion to dry, clean Portland cement concrete. This eliminates the need for primers in most cases, reducing labour time and cost while maintaining high bond strength.
How long does DOWSIL™ 888 take to cure fully?
While the sealant forms a skin within 1 hour, full cure typically occurs within 21 days at 25°C and 50% relative humidity. This timeline ensures maximum mechanical and weather-resistant properties are achieved.
Is DOWSIL™ 888 suitable for use in fuel-exposed areas like petrol stations?
Yes, it is rated for short-term fuel resistance, making it suitable for splash zones such as fuel station forecourts and light aircraft aprons. For continuous fuel immersion, consult Dow’s specialist technical team or Form 62-207 for details.
What standards does DOWSIL™ 888 comply with?
DOWSIL™ 888 meets major civil infrastructure standards including ASTM D5893 Type NS, FAA P-605, SS-S-200E (flame), and EN 14187-5 (hydrolysis). These certifications make it suitable for government, airport, and road authority projects.
Can DOWSIL™ 888 be used in wet conditions or underwater?
No. DOWSIL™ 888 should not be applied in wet or damp joints and is not recommended for continuous water immersion. Ensure concrete is clean, dry, and frost-free before application for best results.
Uses & Benefits
Where to Use
- Roadway concrete pavement joints (sawn or formed)
- Airport taxiways, aprons, and tarmacs
- Fuel station forecourts and refuelling pads
- Concrete loading docks and warehouse drive-ins
- Bridge decks and kerb expansions
- Remedial joint resealing in grind-back overlays
Key Benefits
- Outstanding joint movement performance: +100% / -50%
- No primer required on most clean concrete surfaces
- Fast skin-over and long open time for tooling flexibility
- Resists UV, weathering, and short-term fuel exposure
- Low modulus – prevents edge cracking and stress failure
- Compliant with ASTM D5893, FAA P-605, EN 14187-5
Applying DOWSIL™ 888 Silicone Joint Sealant: Enhanced Protocols & Best Practices
-
1. Surface & Joint Preparation
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.
Method A: New Concrete
Allow concrete to cure properly. Saw-cut joints and remove dust with compressed air. Ensure the surface is free of all contaminants.
Method B: Remedial/Grind-Back Joint
Grind and remove old sealant. Clean with abrasive method and air blowout. Ensure surface is recessed and uniform before installation.
Timing: Do not apply during rain or when concrete is damp. Surface must be fully dry before starting.Pro Tip: Use solvent or mechanical prep on heavily soiled or fuel-contaminated surfaces. -
2. Backer Rod Installation
Insert closed-cell backer rod to control sealant depth and prevent three-sided adhesion. Select appropriate diameter to allow compression during insertion.
Standard Method
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.
Grind-Finished Joint
Account for expected grinding depth — place rod slightly deeper (up to 12.7 mm) so final profile sits correctly below the surface.
Timing: Install backer rod immediately prior to sealant application to avoid contamination.Pro Tip: Never puncture or split the backer rod — air pockets can cause sealant failure. -
3. Sealant Application
Dispense DOWSIL™ 888 using a manual, pneumatic, or bulk pump gun. Apply in a continuous motion to avoid air entrapment.
Cartridge Application
Cut nozzle to match joint width and extrude steadily. Tool immediately to avoid skin formation.
Bulk Pump Application
Use an air-powered system for large jobs. Maintain consistent pressure and flow rate above 72 mL/min.
Timing: Tool within 5–10 minutes. Skin forms in ≤1 hour. Avoid rain exposure during early cure.Pro Tip: Use masking tape on joint edges for cleaner lines and remove before skin-over begins. -
4. Finishing, Curing & Cleanup
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.
Curing Conditions
Allow 21 days at 25°C / 50% RH for full cure. Cooler temps will extend curing time.
Tool Cleanup
Wipe uncured material using xylene or suitable solvent. Do not use water-based cleaners.
Timing: Protect sealant from rain for at least 8 hours after placement.Pro Tip: Do not disturb or traffic over sealant until full cure is reached to avoid damage.
Limitations & Safety Information
Not for Immersed or Wet Surfaces
DOWSIL™ 888 must only be applied to clean, dry, frost-free surfaces. It is not suitable for use in permanently immersed joints or those exposed to standing water prior to cure.
Not for Asphalt or Bitumen
Do not apply to bituminous or oily substrates. For such joints, consider alternative polyurethane-based or hybrid sealants suited to flexible pavements.
Avoid 3-Sided Adhesion
To maintain proper movement capability, always install a backer rod or bond-breaker tape to prevent adhesion on three sides of the joint.
Storage & Shelf Life
Store in original, sealed packaging below 32°C. Use within the shelf life printed on packaging (typically 12 months from manufacture). Protect from freezing.
Material Safety
Contains moisture-curing silicone polymers. Emits methanol vapours during cure. Use in well-ventilated areas. Avoid inhalation or skin contact with uncured product.
Personal Protective Equipment (PPE)
Wear nitrile gloves, safety glasses, and suitable protective clothing. In enclosed areas, use adequate respiratory protection if ventilation is poor.
Disposal
Dispose of uncured product and contaminated materials according to local environmental regulations. Do not pour into drains or watercourses.
First Aid Measures
In case of skin contact, wash with soap and water. For eye exposure, rinse immediately with water and seek medical attention. Refer to SDS for detailed guidance.
DOWSIL™ 888 Silicone Joint Sealant Application Guide
Portland Cement Concrete
Surface Preparation
Ensure the concrete surface is dry, clean, frost-free, and free of loose particles. Remove laitance, form oils, curing compounds, and dust using abrasive wire brushing and compressed air. Ensure no standing water is present.
Primer Requirements
No primer typically required
DOWSIL™ 888 is formulated for unprimed adhesion to Portland cement concrete. However, adhesion testing is recommended for unusual substrates or highly polished surfaces.
Aged or Weathered Concrete
Surface Preparation
Mechanically abrade to expose fresh concrete and remove surface contaminants. Clean using high-pressure air or water-blasting, followed by drying. Ensure substrate is stable with no loose particles.
Primer Requirements
Primer recommended for optimal adhesion
While 888 often adheres well to clean aged concrete, use of Dow-approved primer may improve bond where substrate is porous or poorly cured.
Dow Primer PGrind-Prepared Pavement Joints
Surface Preparation
After grinding, remove dust and debris using compressed air and vacuum methods. Surface should be sound, dry, and free of oils or hydraulic fluids. Adjust sealant depth based on grind level and backer rod placement.
Primer Requirements
No primer typically required
If grind exposes clean concrete, primer is generally not needed. If surface is burnished or polished by machinery, test adhesion or apply primer for best results.
Fuel-Splashed Concrete
Surface Preparation
Thoroughly degrease using an approved solvent to remove oil or fuel residue. Follow with mechanical abrasion and compressed air. Wait for complete drying before sealant application.
Primer Requirements
Primer recommended for optimal adhesion
Fuel-exposed zones may benefit from primer to overcome hydrocarbon contamination. Use Dow Primer P if in doubt.
Dow Primer P
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