Blue-top stakes (grade stakes) mark the design elevation for equipment operators. A wooden hub stake is driven until its top is exactly at the design elevation. A lath set next to it shows the cut (C) or fill (F) amount in decimal feet. The operator grades to the hub top — when the ground reaches hub top elevation, it is at design grade.
What Are Blue-Top Stakes?
The name comes from painting the hub top with blue marking paint so operators can find it from the cab. The hub top is the design finish grade target. The lath tells the operator how much material to cut or add to get there. Blue-tops are the primary grade communication system between the grade checker and equipment operator on jobs not using machine control.
Equipment Needed
- Automatic level or rotating laser with receiver and grade rod
- Hub stakes (2"×2"×12" wood), lath (1/4"×1-1/2"×18"), hammer
- Keel (blue for fill, red for cut) or marking paint
Step-by-Step Workflow
1. Establish Your HI
Shoot the benchmark. Calculate HI = benchmark elevation + backsight rod reading. Re-verify every 2–3 hours or after any instrument move.
2. Calculate the Target Rod Reading
HI = 108.35 ft | Design grade: 106.50 ft
Target = 108.35 − 106.50 = 1.85 ft
3. Drive the Hub to Grade
Hold the rod on the hub top while someone drives it. Watch the rod reading as the hub descends. Stop when the rod reads 1.85 ft and the receiver shows on-grade — the hub top is at design grade. For fill areas where the ground is below design: drive the hub in, measure the rod reading on top, calculate fill depth needed, mark it on the lath.
4. Mark the Lath
- Cut (C): Ground is above design — “C 0.42” in red means cut 0.42 ft.
- Fill (F): Ground is below design — “F 0.67” in blue means add 0.67 ft of fill.
- On grade: Mark “0.00” or “OK” in blue.
5. Paint the Hub Top
Spray blue paint on the hub top. Unpainted hubs in churned soil are nearly impossible to find from a dozer cab.
Hub Spacing Guidelines
| Work Type | Typical Spacing |
|---|---|
| Site grading / pad | 25–50 ft grid |
| Road subgrade | 25–50 ft along CL + both shoulders |
| Drainage swales | 25 ft along channel CL + high/low points |
| Around structures | 10–15 ft |
Common Problems
- Hub driven too deep: Pull it and set a new one. Drive slowly and check frequently as the hub approaches grade.
- Disturbed hub: If equipment runs over a hub, reset it before that area is graded. Never assume a disturbed hub is still at grade.
- HI shift during the day: Re-shoot the benchmark after any break or instrument move. A 0.05-ft HI shift sends every subsequent hub off grade.
See also: Grading Tolerances and Cut and Fill Calculations.