DAP DK Onyx is a synthetic rubber caulk that applies in temperatures from 20°F to 120°F and adheres to wet surfaces — a game-changer for Montana contractors who can’t wait for perfect weather. This professional-grade sealant delivers ±25% joint movement capability, making it flexible enough to handle temperature swings without cracking.
Skip it if you’re looking for budget latex caulk. This is premium sealant for contractors who need Diamond Kote color matching and all-weather performance.
Technical Specifications
The synthetic rubber formula contains 70.8% solids by weight — significantly higher than typical acrylic caulks. Higher solids mean less shrinkage and better long-term performance.
| Specification | Value |
|---|---|
| Base polymer | Synthetic rubber |
| Solids content | 70.8% by weight |
| Application temperature | 20°F to 120°F |
| Joint movement | ±25% (ASTM C719) |
| Coverage | 31 linear feet at 1/4” bead |
| Tooling time | 5 minutes |
| Full cure | 7-14 days |
| ASTM compliance | C920 Class 25 |
The caulk meets ASTM C920 Class 25 standards, certifying it for professional exterior applications with significant movement. It’s also ASTM C1183 freeze-thaw stable — critical for Montana’s temperature cycling.
Diamond Kote Color-Match Performance
DK Onyx (BK009) is specifically color-matched to Diamond Kote® Onyx siding. This isn’t generic black caulk with a fancy name. Diamond Kote contractors know that mismatched sealant ruins the clean lines of engineered wood siding installations.
The self-tooling technology means you get a clean finish without special tools. It repels dust and dirt, keeping those color-matched joints looking sharp years after installation. UV stability prevents the fading that makes cheap caulk look terrible after one Montana summer.
All-Weather Application Capabilities
Here’s where this caulk earns its reputation. It adheres to wet and damp surfaces — no more waiting for morning dew to dry or postponing work after light rain. The rain-ready formula won’t wash away if exposed to rain before full cure.
Application temperature range spans from 20°F to 120°F. That covers everything from late-October cold snaps to July heat. Most acrylic caulks fail below 40°F. This synthetic rubber formula stays workable when other sealants turn to concrete in the tube.
Compatible substrates include wood (painted/unpainted), vinyl, PVC trim, aluminum, fiber cement, engineered wood siding, metal, masonry, stone, glass, ceramic, and stucco. One tube handles multiple materials on the same job.
Installation and Limitations
Surface prep remains critical — surfaces must be clean and free of old caulk, dirt, and contamination. Application requires a minimum 1/4” bead applied in a convex profile to avoid gaps. Clean up excess wet sealant with mineral spirits.
If you’re painting over it, wait the full 7-14 days for complete cure. Rushing paint application is the fastest way to ruin an otherwise professional job.
Not recommended for continuous underwater use, below-grade applications, or for surface defects. This is exterior joint sealant, not foundation waterproofing or crack filler.
Bottom Line
Professional debate exists regarding its sealing longevity compared to dedicated polyurethane or silicone sealants, but for Diamond Kote color-matching with all-weather application, this caulk delivers. The combination of wet-surface adhesion, extreme temperature application range, and rain-ready performance makes it worth considering for time-sensitive exterior projects.
Warranty coverage is limited to 1-year replacement if the product fails when used as directed. Not the longest warranty, but synthetic rubber formulas typically outlast their warranty periods when properly applied.
Frequently Asked Questions
Can DAP DK Onyx be applied in freezing temperatures?
Yes, it applies down to 20°F. Most caulks fail below 40°F, but this synthetic rubber formula remains workable in cold conditions. Store tubes indoors before use for best results.
How long before painting over it?
Wait 7-14 days for full dry through before painting. Temperature and humidity affect cure time. Don’t rush it — premature painting causes adhesion failures.
What’s the actual coverage per tube?
One 10.1 oz tube covers 31 linear feet at 1/4” diameter bead or 14 linear feet at 3/8” diameter bead. Plan accordingly for larger gaps.
Does the color really match Diamond Kote Onyx?
DK Onyx (BK009) is specifically engineered to match Diamond Kote® Onyx siding. It’s highly regarded for its specific siding color-match capabilities by contractors working with engineered wood systems.
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