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newSchoolWorks.com › VoTechWorks › Manufacturing & Marine › Fiberglass / Composites (boatbuilding) › Hand Layup and Wet Lamination for Composite Boatbuilding › Lesson 2
MFG-COMP18-03 · Lesson 2 · 10 clock hours · theory

Reinforcement Materials and Laminate Schedule Reading

Objective. Students will identify woven roving, chopped strand mat, biaxial and triaxial cloth, and core materials by fiber architecture, state their typical areal weights, and extract ply sequence and thickness targets from a written laminate schedule.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed engineer or certified journey-level tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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What Are Reinforcement Materials?

Reinforcement materials are the structural backbone of any fiberglass composite laminate. They carry mechanical loads — tension, compression, shear — while the resin matrix holds them in place and transfers forces between plies. Selecting the right reinforcement for each layer of a hull is not guesswork: it is dictated by a written laminate schedule, which specifies every ply in sequence. Your job as a composite boat builder is to read that schedule accurately and place each material correctly.

Common Reinforcement Types

Chopped Strand Mat (CSM)

CSM consists of short glass fibers — typically 1–2 inches long — held together by a chemical binder. Fibers are randomly oriented, so CSM has roughly equal (isotropic) properties in all in-plane directions. Common areal weight: 1.5 oz/ft² (approximately 450 g/m²). CSM builds thickness quickly, wets out easily, and conforms well to compound curves. It is frequently used as a tie-coat between woven plies or as an initial skin coat because its random fiber orientation helps the laminate bond without print-through. CSM is not suited to primary structural roles where directional strength is required.

Woven Roving (WR)

Woven roving is a heavy, coarse fabric woven from continuous glass rovings at 0° and 90°. The large tows produce a fabric with a distinctive basket-weave appearance. Common areal weight: 24 oz/yd² (approximately 815 g/m²). WR builds structural thickness rapidly and delivers good biaxial strength. It is often alternated with CSM in traditional hand-layup schedules because the CSM layer absorbs excess resin from the WR and improves interlaminar bonding. WR's crimp at weave crossovers slightly reduces in-plane stiffness compared to non-crimp fabrics.

Biaxial Cloth (0°/90° or ±45°)

Biaxial fabrics are non-crimp fabrics (NCF) in which two layers of continuous fibers are stitched together rather than woven. The two fiber directions can be 0°/90° or ±45°, depending on the specification. Common areal weight: 17 oz/yd² (approximately 580 g/m²). Because fibers lie flat (no crimp), biaxial cloth achieves higher mechanical properties per unit weight than woven roving. Biaxial ±45° cloth is particularly effective at resisting shear and torsion — important in hull panels and deck structures.

Triaxial Cloth (0°/±45°)

Triaxial cloth stitches three fiber layers together: typically 0°, +45°, and −45°. Common areal weight: 54 oz/yd² (approximately 1,830 g/m²). This architecture provides strength in three directions simultaneously, making triaxial cloth efficient in areas requiring both longitudinal stiffness and shear resistance — such as stringers, transom reinforcement, and high-load attachment points. A single heavy triaxial ply can replace several thinner plies, reducing layup time.

Core Materials

Sandwich construction places a lightweight core between two structural skins to increase panel stiffness without a large weight penalty — the same principle as an I-beam. The skins carry tension and compression; the core carries shear.

Both cores are supplied in sheet or contoured (scored/kerfed) form for conforming to curved surfaces.

Reading a Laminate Schedule

A laminate schedule is a table or numbered list that specifies, for each zone of a structure:

1. Ply number — the sequence from mold surface outward

2. Material type — e.g., 1.5 oz CSM, 24 oz WR, 17 oz biaxial

3. Number of layers — how many plies of that material

4. Fiber orientation — angle relative to a reference axis (0° = keel centerline in many hull schedules)

5. Cumulative thickness or weight — a running total used to verify the build

6. Transition zones — locations where the schedule changes (e.g., hull bottom to topsides, or where a core begins and ends)

When reading a schedule, first identify the gel coat (not a structural ply), then work outward ply by ply. Highlight transitions where core begins or where heavy reinforcement is called out for a specific structural reason. Check that your cumulative thickness matches the target at each checkpoint specified in the schedule.

Fiber Architecture and Structural Role — Summary

| Material | Architecture | Typical Weight | Primary Structural Role |

|---|---|---|---|

| CSM 1.5 oz | Random | 1.5 oz/ft² | Tie coat, skin coat, conformability |

| Woven Roving 24 oz | 0°/90° woven | 24 oz/yd² | Bulk thickness, biaxial strength |

| Biaxial 17 oz | 0°/90° or ±45° NCF | 17 oz/yd² | Efficient biaxial or shear reinforcement |

| Triaxial 54 oz | 0°/±45° NCF | 54 oz/yd² | Multi-directional, high-load zones |

| Corecell foam | — | Varies by density | Shear core, sandwich stiffness |

| Balsa core | — | Varies | Shear core, high compressive stiffness |

Safety Notes

Key terms9

Areal weightThe mass of a reinforcement fabric per unit area (oz/yd² or g/m²), used to specify and verify the amount of fiber in each ply.
Chopped Strand Mat (CSM)A reinforcement made from randomly oriented short glass fibers held by a binder; provides isotropic in-plane properties and good conformability to complex curves.
Woven Roving (WR)A heavy coarse fabric woven from continuous glass rovings at 0° and 90°; builds structural thickness rapidly and provides biaxial strength.
Non-crimp fabric (NCF)A reinforcement in which straight fiber layers are stitched together rather than woven, eliminating fiber crimp and delivering higher mechanical properties per unit weight than woven equivalents.
Biaxial clothAn NCF with fibers oriented in two directions (0°/90° or ±45°); effective for panels requiring strength in two directions or shear resistance.
Triaxial clothAn NCF with fibers in three directions (typically 0°/+45°/−45°); used in high-load zones where multi-directional strength is needed in a single efficient ply.
Sandwich constructionA laminate design in which a lightweight core material is bonded between two structural fiber-reinforced skins to maximize panel stiffness at low weight.
Laminate scheduleA written engineering document that specifies the exact sequence, type, orientation, and quantity of each ply in a composite structure, along with cumulative thickness targets.
Transition zoneA location in a laminate schedule where the ply sequence or core material changes, such as the boundary between a sandwich panel and a solid laminate flange.

Worked examples4

1. A laminate schedule calls for the following plies in a hull bottom section (working outward from the mold): Ply 1 — 1.5 oz CSM; Ply 2 — 24 oz WR; Ply 3 — 1.5 oz CSM; Ply 4 — 24 oz WR. The fabricator estimates each 1.5 oz CSM ply adds approximately 0.030 in and each 24 oz WR ply adds approximately 0.060 in to the cured laminate. What is the estimated cumulative thickness after all four plies?
  1. Identify the thickness contribution of each ply: CSM 1.5 oz = 0.030 in; WR 24 oz = 0.060 in.
  2. List the four plies in order: Ply 1 CSM (0.030 in), Ply 2 WR (0.060 in), Ply 3 CSM (0.030 in), Ply 4 WR (0.060 in).
  3. Add all values: 0.030 + 0.060 + 0.030 + 0.060 = 0.180 in.
  4. State the cumulative thickness: 0.180 in after four plies.
Answer: Estimated cumulative laminate thickness = 0.180 in.
2. A schedule section shows 3 plies of 17 oz biaxial cloth. Each ply of 17 oz biaxial is estimated to add approximately 0.025 in to the cured laminate. What is the estimated thickness contribution of this biaxial section alone?
  1. Identify the ply count: 3 plies of 17 oz biaxial.
  2. Identify the thickness per ply: 0.025 in.
  3. Multiply: 3 × 0.025 in = 0.075 in.
  4. State the answer.
Answer: Three plies of 17 oz biaxial cloth contribute an estimated 0.075 in to the laminate thickness.
3. You are verifying a laminate schedule for a transom. The schedule specifies: 1 ply 1.5 oz CSM (0.030 in), 2 plies 24 oz WR (0.060 in each), 1 ply 54 oz triaxial (0.080 in), and 1 ply 1.5 oz CSM (0.030 in). What is the estimated total cured thickness?
  1. List each ply and its thickness: CSM = 0.030 in; WR ply 1 = 0.060 in; WR ply 2 = 0.060 in; Triaxial = 0.080 in; CSM = 0.030 in.
  2. Sum all values: 0.030 + 0.060 + 0.060 + 0.080 + 0.030.
  3. Calculate: 0.030 + 0.060 = 0.090; 0.090 + 0.060 = 0.150; 0.150 + 0.080 = 0.230; 0.230 + 0.030 = 0.260 in.
  4. State the total.
Answer: Estimated total cured thickness of the transom laminate = 0.260 in.
4. A laminate schedule lists a target skin laminate weight of 3 plies of 24 oz WR. If you are using 17 oz biaxial instead to achieve the same total fiber areal weight per ply count, approximately how many plies of 17 oz biaxial would provide a similar total areal weight to 3 plies of 24 oz WR?
  1. Calculate total areal weight of WR section: 3 × 24 oz/yd² = 72 oz/yd².
  2. Divide by weight per biaxial ply: 72 oz/yd² ÷ 17 oz/yd² ≈ 4.24 plies.
  3. Round up to the nearest whole ply to meet or exceed the target: 5 plies of 17 oz biaxial.
  4. Note: always verify substitutions with the engineer or schedule designer before making changes in production.
Answer: Approximately 5 plies of 17 oz biaxial cloth would be needed to match or exceed the areal weight of 3 plies of 24 oz WR (total 72 oz/yd²). Any ply substitution requires engineering approval.

The math in this lesson2

Learners convert 24 oz WR plies to an equivalent number of 17 oz biaxial plies by areal weight.
6.RP.37.EE.3
In class: Instructor demonstration with a cut library of reinforcement samples: students handle each type, record fiber architecture, areal weight, and intended structural role on a comparison chart. · Laminate schedule reading exercise: instructor distributes a sample ABYC-style laminate schedule for a 24-foot hull section; students highlight each ply type, cumulative thickness, and transition zones, then answer five comprehension questions. · Pairing exercise: students match five reinforcement samples to their correct position in the laminate schedule, justifying each choice with a written sentence referencing fiber orientation or weight requirements.
Materials: Reinforcement sample library (1.5 oz CSM, 24 oz WR, 17 oz biaxial, 54 oz triaxial, Corecell foam core, balsa core), sample laminate schedule document, ACMA textbook Chapter on reinforcements, rulers, marker pens
Check: Identification worksheet: students correctly label all seven reinforcement samples and answer all five schedule comprehension questions; pass = 80% correct.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Reinforcement Materials and Laminate Design
1. Which fiber architecture makes chopped strand mat (CSM) behave in an approximately isotropic manner within the plane of the laminate?
Reinforcement Materials and Laminate Design
2. A laminate schedule specifies 24 oz WR. What does '24 oz' refer to?
Reinforcement Materials and Laminate Design
3. A boatbuilder needs to reinforce a hull panel that experiences significant shear loading. Which reinforcement architecture is most effective for resisting in-plane shear?
Sandwich Construction and Core Materials
4. What is the primary structural function of a core material such as Corecell foam or end-grain balsa in a sandwich laminate?
Laminate Schedule Interpretation
5. When reading a laminate schedule, what information does the 'transition zone' notation communicate to the builder?
Core Materials and Moisture Protection
6. Why is end-grain balsa core considered higher risk than closed-cell foam core in areas where through-hull fittings or penetrations will be made?
Laminate Schedule Interpretation and Measurement
7. A laminate schedule shows the following ply sequence: (1) 1.5 oz CSM, (2) 24 oz WR, (3) 1.5 oz CSM, (4) 24 oz WR. Using estimated cured thicknesses of 0.030 in per CSM ply and 0.060 in per WR ply, what is the estimated total cured laminate thickness?
Safety, PPE, and Hazard Control
8. During dry fabric handling and cutting operations in the shop, which minimum respiratory protection is appropriate to protect against respirable glass fibers?
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