Vacuum Bagging Technique: Single-sided Bagging 230

This class covers basic procedures for performing single-sided vacuum bagging. It also covers general safety precautions and strategies for preventing common problems.

  • Difficulty Intermediate

  • Format Online

  • Number of Lessons 15

  • Language English


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Course Outline
  • Objectives
  • Vacuum Bagging Techniques
  • The Components of a Vacuum Bagging System
  • Taking Safety Precautions
  • Preparing for a Vacuum Bagging Job
  • Preparing the Mold
  • Dispensing and Mixing the Resin
  • Building the Composite Laminate
  • Placing the Peel Ply and Release Film
  • Placing the Bleeder and Breather Plies
  • Installing the Vacuum Port
  • Sealing the Vacuum Bag Effectively
  • Debulking and Curing
  • Cleaning Up
  • Summary
  • Distinguish between different vacuum bagging techniques.
  • List the components of a vacuum bagging system.
  • Describe the safety precautions required for vacuum bagging.
  • Explain how to set up and organize the work area for a vacuum bagging job.
  • Explain how to prepare an open mold for a vacuum bagging job.
  • Explain how to dispense and mix the resin and hardener.
  • Explain how to build a composite laminate by hand lay-up.
  • Explain how to place the peel ply and release film onto a composite laminate.
  • Explain how to place the bleeder and breather ply within the vacuum bagging assembly.
  • Explain how to install a vacuum port onto a vacuum bag.
  • Explain how to prevent bridging and seal the vacuum bag.
  • Explain how to debulk and cure a vacuum bagged part.
  • Describe how to clean up after a vacuum bagging job.
Vocabulary Term


A solvent that may be used to clean certain types of resins from a surface. Acetone is highly flammable.

arm coverings

Fabric or leather sleeves that fit over the arms to protect from various hazards. When working with resins, it is advisable to wear arm coverings or long sleeves.

bagging materials

The various plies of film and material that are layered over the composite part. Vacuum bagging materials are often referred to as consumables because they can be used only once before being discarded.

bleeder ply

A thick fabric that absorbs excess resin. The bleeder ply is placed over the release film in a vacuum bagging system.

breather ply

A thick fabric that regulates the pressure within the vacuum bagging system. The breather ply is often made of the same material as the bleeder ply, and a single piece of fabric may be used as both the bleeder and the breather.

breathing mask

A protective covering that fits over the nose and mouth. Breathing masks protect the operator from inhaling airborne particles and certain types of fumes.


A problem in vacuum bagging that occurs when the bag stretches over an area of the composite laminate instead of pressing against it. Bridging prevents proper compression of the composite laminate and results in uneven resin distribution.


A non-porous synthetic rubber that offers better protection from certain chemicals, such as some ketones, than other rubber or rubber-like materials. Safety gloves made of butyl provide good protection against resins and hardeners.


A plate or pad placed over a vacuum bagging assembly. Cauls apply pressure to a specific area and prevent bridging.


The various plies of film and material that are layered over the composite part. Vacuum bagging materials are often referred to as consumables because they can only be used once before being discarded.

control valve

A valve with a variable opening that allows the flow of air in a vacuum system to be increased or decreased. Control valves are used to control the rate at which resin flows through the reinforcement fibers.


A mechanical fitting used to attach the vacuum hose to the vacuum bag.


The process of removing air from a composite laminate or prepreg. Debulking increases the density of the composite laminate.

double-sided bagging

A vacuum bagging technique during which the vacuum bag surrounds the entire part rather than simply covering the exposed side of the part.

exothermic reaction

A chemical reaction that releases heat. Mixing resin and hardener may cause an exothermic reaction within the container.

gel coat

A coating that is usually applied to the mold's surface before forming the composite part. Gel coat protects the surface of the composite and gives it a smooth finish.

graduated container

A container made of a heavy-duty semi-transparent plastic that is impervious to the resin being used. Graduated containers allow the operator to accurately measure the amount of resin poured into the container.

hand lay-up

A manual molding process during which reinforcement in the form of a fabric or a mat is positioned into the mold and saturated with a resin. Also called lay-up molding.


The chemical symbol for mercury. In vacuum bagging, vacuum pressure is measured in inches of mercury.


An ingredient used to facilitate chemical reactions. The operator must add an initiator to the gel coat before applying it to the mold.


Two or more layers of fibrous material that have been bonded together for strength. Vacuum bagging is used for compressing and curing composite laminates.

lay-up molding

A manual molding process during which reinforcement in the form of a fabric or a mat is positioned into the mold and saturated with a resin. Also called hand lay-up.


A device for distributing vacuum pressure more evenly through the vacuum system. Manifolds are typically used for vacuum bagging large parts.

mastic tape

A sticky strip of material used to seal the vacuum bag to the mold. Mastic tape has protective backing that should be left on the tape until the operator is ready to seal the bag to the mold.

material safety data sheet

Mandatory information that must accompany almost every chemical in the workplace except for items like cleaning supplies. An MSDS includes details such as the hazards, precautions, and first-aid procedures associated with the chemical.

mil gage

A device used to measure the thickness of gel coat.


A tool for forming composite parts. Vacuum bagging is typically done on parts that have been created on an open mold.

open mold

An open cavity that has no rigid second piece to enclose the part and apply pressure. Vacuum bagging is typically done on parts that have been created on open molds.


The Occupational Safety and Health Administration. A government agency that sets the standards for working conditions in the United States and ensures that employees work in safe and healthy environments.

paste wax

A release material applied to composite molds. Paste wax is soft and never fully dries so it is easy to remove.

peel ply

An optional layer of fabric placed between the composite part and the release film. The peel ply may be used to give texture to the part's surface or to protect it from contaminants during the vacuum bagging process.


An interface that links one device with another. During vacuum bagging, the port connects the vacuum hose to the vacuum bag.

product data sheet

A document providing critical information about the ingredients of a resin and instructions for its use. Always consult the manufacturer's product data sheet before mixing resin and hardener.

reinforcement form

The length and arrangement of the reinforcement fibers. Common forms include continuous fiber roving, woven roving, veil, and mat.

release film

A thin, stretchy plastic film that facilitates pulling the various vacuum bagging materials off a composite part.

resin system

All of the ingredients required to create the chemical reactions for cross-linking and hardening the resin. Catalysts and hardeners are considered part of the resin system.


A breathing device worn to prevent inhalation of hazardous substances. Respirators may purify air from the environment or supply air to the wearer.

safety disposal can

A container used for storing and disposing up to five gallons of industrial waste, including flammable and combustible liquids.

safety glasses

Protective eyeglasses with metal or plastic frames and impact-resistant lenses that may or may not offer vision correction. Many safety glasses also have protective side shields.

safety gloves

Personal protective equipment worn over the hands. When handling resins, the operator should wear safety gloves made from butyl or another material that is impervious to resin.

single-sided bagging

A vacuum bagging technique during which a sheet of plastic is sealed to the outer rim of the mold.

spray-up molding

A manual molding process during which an operator uses a spray machine to simultaneously apply resin and chopped fiberglass strands to an open mold.


A colorless and toxic hydrocarbon used in plastics. Many of the resins used in pultrusion emit styrene vapors that may be harmful to the operator if inhaled.

surface bagging

A vacuum bagging technique typically used for making repairs on composite parts. After holes have been filled or damaged areas replaced, the vacuum bag is placed over the repair and sealed around the perimeter of the repair area.

vacuum bag

A thick, stretchy plastic bag that covers the composite laminate and the rest of the vacuum bagging materials. Vacuum bags must be able to withstand vacuum forces and curing temperatures without breaking.

vacuum bagging

A type of compression molding in which a bag is placed over the mold and a vacuum pump draws the air out. Vacuum bagging compresses the composite laminate and squeezes out any air or excess resin

vacuum bagging assembly

The collective term for a composite that has been covered with plies of vacuum bagging film and the vacuum bag.

vacuum cup

A hollow suction cup used as a simple port for the vacuum hose.

vacuum envelope

The airtight enclosure created by a sealed vacuum bag.

vacuum equipment

The parts of the vacuum bagging system that control airflow. The airflow control system must be airtight to allow the best vacuum pressure.

vacuum gage

An instrument for monitoring the air pressure within a vacuum bag. Vacuum gages measure vacuum pressure in atmospheres.

vacuum hose

The part of the vacuum system that channels the airflow between the vacuum bag and the vacuum pump. Also known as the vacuum line.

vacuum line

The part of the vacuum system that channels the airflow between the vacuum bag and the vacuum pump. Also known as the vacuum hose.

vacuum pump

A device that draws air out of a closed system. In vacuum bagging, the vacuum pump removes air from the sealed vacuum bag.