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A single-component, moisture-curing polyurethane binder blended with clean, washed stone to build a permeable, durable bonded-stone surface. Clear and Amber install the same way — this guide covers the recommended mix method, coverage rates, and handling details, step by step.
Gravel-Lok comes in two formulas — Clear and Amber — that install in exactly the same way; the only difference is appearance and recommended use. The steps below apply to both. Choose your formula first, then follow the mix method for a permeable surface suited to paths, patios, tree pits, and drainage edges.
Both formulas use the identical installation process, coverage rates, and cure requirements. Choose based on the look you want and how the surface will be used.
Deciding between the two? See the Color Comparison (Amber vs. Clear) guide for side-by-side visuals.
Use clean, washed stone so the binder can bond. Both rounded and angular stone work — angular stone interlocks and adds stability over time.
Finished depth should be at least 3× your stone size — ½" stone needs 1.5" minimum. The pour method needs 2.5" minimum.
Install only when temperatures hold between 50°F and 90°F for 24 hours after application. Cold or damp air stalls the cure.
Stone must be 100% dry before mixing. Residual moisture makes the resin set too fast — a common cause of premature hardening.
The mix method suits most residential paths and patios: blend binder into the stone in a bucket, place it, level it, let it cure, then seal the top with a roll coat.
Rinse aggregate to remove dust and fines, then let it dry completely. Dry stone is non-negotiable — trapped moisture accelerates the reaction and a batch can set before you place it.
Stone: washed, rounded or angular Moisture: 100% dry
Work in batches of roughly one 5-gallon bucket of stone (about 50 lbs). Add binder to the stone — never over the limit, or the mix foams and weakens.
Max: 20–24 oz liquid Per: 5-gal bucket (~50 lb)
Blend thoroughly — a drill paddle or mortar mixer works well — until each stone carries a thin, even film of binder. Consistent coating gives the finished surface its strength.
Look for: uniform sheen Avoid: pooling / foam
Lay a geotextile separation fabric across the prepared base before placing stone. It separates the aggregate from the subgrade, stabilizes the surface, and helps maintain permeability over time. Overlap seams and extend the fabric to the edges of the installation area.
Function: separation + stabilization Seams: overlap, cover full area
Spread the coated stone over your prepared base and screed it level. Keep finished depth at least three times the stone diameter so the surface locks together and stays put.
Min depth: 3× stone size Concrete base? wet roll coat first
Leave the placed surface undisturbed to moisture-cure for at least 24 hours within the temperature window. Once it has cured, apply a light roll coat of binder across the top to lock the surface and add sheen.
Cure first: 50–90°F, 24 hrs+ Then roll coat: ~90 SF / galCoverage depends on depth and method. These are the published rates — plan the roll coat separately from the mix or pour.
| Finished thickness | Coverage | Notes |
|---|---|---|
| 1" | 37.2 SF / gal | Thinnest usable layer |
| 1.5" | 24.8 SF / gal | Common path depth |
| 2" | 18.6 SF / gal | Heavier-use surfaces |
| Roll coat | 90 SF / gal | Top seal, applied separately |
| Application | Coverage | Notes |
|---|---|---|
| 1 light pour | 19 SF / gal | Poured onto dry stone |
| 2 light pours | 14 SF / gal combined | Recommended for durability |
| Roll coat | 90 SF / gal | Top seal, applied separately |
One 5-gallon container ≈ 640 oz of binder. At the 20–24 oz-per-bucket mix rate that covers a substantial area — run your exact square footage through the Gravel-Lok Coverage Calculator for a precise number.
Don't over-add binder. Staying at or below 20–24 oz per 5-gallon bucket of stone prevents foaming. Excess liquid weakens the bond and clouds the finish.
Wet stone sets fast. If a batch starts hardening sooner than expected, the stone likely wasn't fully dry after washing. Dry thoroughly before mixing.
Match the formula to your stone. Clear is UV-stable and won't discolor light or white stone. Amber is not UV-stable and will tint light stone with a warm matte finish that develops over 2–6 months — great on darker stone, but not for keeping whites bright.
Installing over concrete? Add a roll coat to the concrete and, while it's still wet, place the mixed Gravel-Lok stone on top so it bonds to the slab.
Want ADA compliance? Use 1/8" to 1/2" size stones. The bonded surface stays firm, stable, and permeable at that gradation.