TopCast Finish: Grades, Application & Wash-Off Guide
TopCast is not a metal coating or a final concrete sealer. It is a water-based top-surface retarder used on fresh concrete to create a controlled exposed-aggregate finish. The selected grade delays only the surface paste; after the slab gains enough strength, that paste is washed away to reveal aggregate.
The finish depends on the concrete mix, aggregate, grade number, application rate, weather, finishing method, and wash-off timing. Dayton Superior therefore recommends a mockup made with the actual mix and jobsite technique before the production pour.
TopCast Finish at a Glance
Apply TopCast uniformly after the initial bleed water has evaporated, using a compatible low-pressure sprayer and a complete hiding coat. The bulk concrete continues hardening while the surface matrix is delayed. Removal may occur roughly 4–16 hours later, but hot weather or fast-setting concrete can require same-day wash-off.
| Grade | Package color | Approximate effect or exposure |
|---|---|---|
| 03 | Violet | Acid-etch effect |
| 05 | Light blue | Sandblast effect |
| 15 | Yellow | Up to 1/4 in. (6.5 mm) |
| 25 | Beige | 1/8–1/4 in. (3–6.5 mm) |
| 50 or 75 | Canary green or blue | 1/8–3/8 in. (3–9.5 mm) |
| 100 | Gray | 3/8–1/2 in. (9.5–13 mm) |
| 125 or 150 | Pink or green | 3/8–5/8 in. (9.5–16 mm) |
| 200 | Salmon | 5/8–1 in. (16–25 mm) |
| 250 | Orange | 1–1 1/2 in. (25–38 mm) |
The manufacturer labels these as estimated results for standard mix conditions; they are not guaranteed depths. Use the current TopCast technical data sheet and a mockup to confirm the grade.
Application Sequence
- Choose aggregate, mix design, finishing method, and target exposure together. The retarder cannot expose aggregate that was pushed too deep during finishing.
- Place and finish the concrete without overworking the surface. Wait for the initial bleed water to evaporate.
- Mix the TopCast and strain it when filling the sprayer, following the current product instructions.
- Spray a uniform hiding coat. Thin, streaky coverage can create uneven exposure.
- Protect the area from traffic and monitor temperature, wind, shade, and concrete set.
- At the mockup-confirmed time, remove the delayed paste with water and a stiff broom or suitable pressure washing method.
- Rinse clean, inspect the exposure, allow the surface to dry, and apply only a compatible sealer when specified.
Wash-Off Timing Matters More Than the Clock
The official range is broad because concrete does not set by the clock alone. Cement content, admixtures, slab temperature, wind, shade, finishing, and TopCast grade all affect removal. Washing too early can pull aggregate loose or create ruts; washing too late can make the paste difficult to remove and cause blotchy exposure.
A test panel placed beside the production slab gives the crew a realistic wash-off reference. The manufacturer’s TopCast user guide also explains grade selection, sprayer use, mix considerations, and troubleshooting.
Common TopCast Problems
| Problem | Likely cause | Prevention |
|---|---|---|
| Uneven or streaky exposure | Inconsistent spray coat or surface finishing | Use a mockup, maintain sprayer pressure, overlap passes |
| Aggregate pulls out | Washed too early or weak surface | Confirm set on the mockup; reduce wash aggression |
| Paste is hard to remove | Washed too late, hot weather, or light grade | Monitor conditions and begin sooner when required |
| Finish is deeper than expected | Grade/mix mismatch or aggressive washing | Choose grade with actual aggregate and mix |
Sealing and Maintenance
TopCast creates the texture; it does not make the concrete stain-proof. After wash-off and drying, choose a sealer compatible with the manufacturer’s system and the desired sheen, traction, and exposure. Avoid assuming a glossy sealer is appropriate for every walking surface, especially where wet slip resistance matters.
Bottom Line
A successful TopCast finish is planned as a system: mix, aggregate, grade, application, weather, removal timing, and sealer. The mockup is not optional guesswork—it is the quickest way to confirm that the selected grade and wash schedule will create the intended appearance.
Frequently Asked Questions
What is a TopCast finish?
A TopCast finish is exposed-aggregate concrete made with a water-based surface retarder. The retarder delays hardening of the top cement paste so it can be washed away and reveal the selected aggregate.
When should TopCast be washed off?
Dayton Superior says removal can be as early as about 4 hours and up to about 16 hours, depending on mix design, grade, finishing, temperature, humidity, and weather. A jobsite mockup is the safest timing guide.
Does a higher TopCast number expose more aggregate?
Generally, yes. The numbered grades correspond to progressively deeper etch ranges, but the final appearance also depends on aggregate size, mix design, finishing, application rate, and wash-off timing.
Is TopCast a concrete sealer?
No. The main TopCast product is a surface retarder used before wash-off. Protection or sheen requires a compatible sealer selected after the exposed surface is cleaned and dry.
Can TopCast be applied to old concrete?
It is intended for freshly placed concrete because it delays the surface cement paste. It does not recreate the same controlled exposure on an already cured slab.
