Corbel Calculation & Coating Guide

How corbel dimensions map to calculator fields, which surfaces get coated, and how costs are computed.

1. Corbel Anatomy (Side View)

A corbel is a decorative bracket viewed from its side profile. The profile shape is the cross-section; the depth is how thick the piece is.

Coated surface

Not coated

Five surfaces:

A side (back) — flat against the wall, not coated
Top — flat against ceiling/header, not coated
Front contour — the decorative curve, coated
Left side — exposed profile face, coated
Right side — exposed profile face, coated

Perimeter = total outline of the profile (all sides). Measured from the DXF or CAD drawing of the corbel cross-section.

Coating Override = perimeter minus the two uncoated faces (A side + top).

Corbels vs Cornices: Corbels are standalone brackets — both side faces are exposed and coated. Cornices run continuously along a wall — the side faces butt against adjacent pieces and are not coated. The coating override formula is the same; the difference is in the total surface area (corbels add two side faces).

2. Calculator Field Mapping

How physical dimensions map to the calculator's Item Input fields:

Calculator Field	Corbel Meaning	Example (COR-105 Custom)
H (Height)	Profile height — vertical span against the wall = A size	8"
W (Width)	Profile width — horizontal span along the ceiling	24"
L (Length)	Depth/thickness of the piece (into the page)	6"
A Size	Same as H for corbels	8
Perimeter	Full cross-section contour from DXF/CAD (all sides)	61.14"
Coating Override	Perimeter minus A side minus top = coated contour only	29.14"
Corners	Mesh hand-press points on the profile contour	7
Coating Mode	Manual (hand-applied for all corbels)	Manual

Why Coating Override? The auto formula only subtracts the A side: coatingLength = perimeter - aSize. For corbels, the top face is also hidden (against the ceiling), so you must manually override: coatingOverride = perimeter - H - topWidth.

3. What Gets Coated (3D View)

Corbels have three coated surface groups:

Front contour — decorative curve extruded along the depth (L)
Near side — exposed profile face
Far side — exposed profile face

Surface area formulas:

frontArea = (coatingCalc / 12) × (L / 12)
= (29.14/12) × (6/12) = 1.21 sq ft

sideArea = H × W / 2 / 144 (triangle approximation, per side)
= 8 × 24 / 2 / 144 = 0.67 sq ft each

coatSurfArea = frontArea + 2 × sideArea
= 1.21 + 2 × 0.67 = 2.54 sq ft

The "Coat Sides" checkbox in the calculator toggles the side face area. All material costs (mesh, glue, base coat) and labor coating use this total surface area.

Cornices are different: Cornice pieces run end-to-end along a wall, so the side faces butt against adjacent pieces and are not coated. Only the front contour surface applies.

4. Step-by-Step Cost Calculation

Example using COR-105 Custom 8x24 (H=8, W=24, L=6, perimeter=61.14, coatingOverride=29.14):

1Geometry

perimeter = 61.14" (from override, actual profile contour)
coatingLength = 61.14 - 8 = 53.14" (auto: perimeter - aSize)
coatingCalc = 29.14" (override: excludes top + A side)
lengthFactor = 6 / 12 = 0.5 ft
sideArea = 8 × 24 / 2 / 144 = 0.67 sq ft (per side)
coatSurfArea = (29.14/12) × 0.5 + 2 × 0.67 = 2.54 sq ft

2Foam Cost

foamCost = ((8.2 × 24.2 × 6) × $0.00149) / 1 piece
= 1,190.64 cu in × $0.00149 = $1.77

Foam block = (H+0.2) × (W+0.2) × L. The 0.2" margin accounts for cutting tolerance.

3Mesh & Glue

meshLengthWithOverlap = 29.14 + 4 = 33.14"
meshArea = (33.14/12) × 0.5 + 2 × 0.67 = 2.72 sq ft
meshCost = ($30.64 / 475) × 2.72 = $0.18
glueCost = $0.2237 × 2.72 = $0.61

Mesh and glue cover the front contour (with 4" overlap) plus both side faces.

4Base Coat

cementCostPerSqFt = $12 / 30 = $0.40/sq ft
baseCost = $0.40 × 2.54 sq ft = $1.02

Uses full coatSurfArea (front contour + both side faces).

5Labor — Manual Meshing (new May 2026)

coatSurfArea = 2.54 sq ft
manualMeshHrs = manualMeshK × 2.54^manualMeshP
= 0.0662 × 2.54^0.878 = 0.149 hrs (8.9 min)
laborGlue = 0.149 × $20 × 1 crew = $2.98

Corbels now use the manualMesh power-law curve instead of the old corner-based formula. The curve is anchored at (1.30 sqft = 5 min) and (6.31 sqft = 20 min), based on the cap surface-area range. The 8H×24L×6W corbel hits ~12 min meshing — matches Aaron's stopwatch reference of 10–15 min.

6Labor — Manual Coating

coatSurfArea = 2.54 sq ft
manualCoatHrs = manualK × 2.54^manualP
= 0.0542 × 2.54^0.864 = 0.121 hrs (7.3 min)
laborCoating = 0.121 × $20 × 1 crew = $2.42

Manual coating curve was recalibrated May 2026 to anchor on real production data: (3.67 sqft = 10 min) at the small end, (29.19 sqft = 60 min) at the large end. Old curve over-predicted coating time by ~3× for small pieces.

7Per-item time overrides (optional)

If you have a stopwatch reading for a specific corbel, you can lock that piece's labor times directly in the catalog editor:

manualCoatMin — coating time in minutes (overrides the curve)
manualMeshMin — meshing time in minutes (overrides the curve)

When set, these bypass the curve entirely. Leave blank to fall back to the curve.

8Totals

materialTotal = foam + mesh + glue + base coat
laborTotal = (cutting + meshCut + meshing + coating) × 1.15
total = materialTotal + laborTotal
totalWaste = total × 1.05
listPrice = totalWaste × 3

5. Standard vs Custom Corbels

Attribute	Standard Catalog Corbels	Custom Corbels
Category	Corbels	Custom
Perimeter	Auto: (H+W)×2	Override from DXF/CAD measurement
Coating Override	Not set (auto: perimeter - aSize)	Set to: perimeter - H - topWidth
Length (L)	Small (3"–6" typical)	Any size
Coating Mode	Manual (locked, May 2026)	Manual (locked)
manual_only flag	1 (forced)	1 (forced for Custom corbels)
Waste Mult	1.05 (5%)	1.05 (5%)
Labor Coat Mult	n/a (machine mode unused)	n/a
manual_coat_min override	blank (uses curve)	Optional — set if stopwatch known
manual_mesh_min override	blank (uses curve)	Optional — set if stopwatch known

Standard catalog corbels use auto-calculated perimeters (H+W)×2, which approximates the profile as a rectangle. This works well enough for small catalog sizes where the decorative curve is close to a rectangular bounding box.

Custom corbels should always use measured perimeter and coating overrides for accuracy, especially for larger or unusually shaped pieces.

What changed in May 2026: Corbels are now flagged manual_only=1, which means:

Coating mode is locked to manual — the machine option is hidden in the catalog editor.
Has Template checkbox is hidden (templates require machine coating).
Meshing labor uses a power-law curve based on coatSurfArea (was: corner count × flat rate).
Coating curve was recalibrated against real production data — small corbels now price ~30% lower, larger corbels stay similar.
Two new optional fields: manualCoatMin and manualMeshMin let you override either curve with a stopwatch reading per item.

6. Key Formula Differences for Corbels

Corbels are not columns or post caps, so they use the default (trim) branch of each formula, but with L ≠ 96:

Formula	Standard Trim (L=96)	Corbels (L varies)
lengthFactor	96 / 12 = 8 ft	L / 12 (e.g. 6/12 = 0.5 ft)
coatingCalc	perimeter - aSize	coatingOverride (if set)
coatSurfArea	(coatingCalc/12) × 8	(coatingCalc/12) × (L/12)
baseCostCalc	$0.40 × (coatingCalc/12) × 8	$0.40 × (coatingCalc/12) × (L/12)

Last updated: May 2026 (manual_only refactor). See Formula Reference for complete formula documentation. See Cornice Guide and Column Guide for related guides.