This information is reprinted with permission from the DERAKANE NEWS ® , The Dow Chemical Company, Vol. 15, Issue 3, January 1997
Because physical inspection of a composite laminate tends to be destructive, visual inspection is usually the method of choice for evaluating composite equipment. This is a list of defects that may aid in the identification of fabrication problems, facilitating their correction & ensuring the ultimate strength & corrosion resistance of the composite part.
Potential Problem / Defect : "Air Bubbles , Voids"
Nature of Defect : Air entrapment between plies, non-interconnected spherical voids
Possible Causes : (Whipping action during mixing) (Poor or dirty surface) (Air bubbles not rolled out during lay-up)

Potential Problem / Defect : "Blisters"
Nature of Defect : Rounded, sometimes sharply defined elevations of laminate surface
Possible Causes : (Cure too rapid) (Moisture in resin, filler or glass)

Potential Problem / Defect : "Impact Cracks"
Nature of Defect : Separation of materials through thickness and visible on surface
Possible Causes : (Impact) (Insufficient reinforcement) (High concentration of resin)

Potential Problem / Defect : "Crazing"
Nature of Defect : Pattern of fine cracks on or beneath surface
Possible Causes : (Isolated resin-rich area) (Impact) (Intermittent service causing temperature differences) (Wet / Dry cycling) (Resin shrinkage)

Potential Problem / Defect : "Delamination"
Nature of Defect :  Separation of layers
Possible Causes : (Poor glass saturation) (Dirty surface) (Glass content too high) (Failure to remove air-inhibition coat before adding layer)

Potential Problem / Defect : "Fisheye"   
Nature of Defect : Small globular mass not blended into surrounding material, particlarly evident in transparent or translucent materials
Possible Causes : (Dirty surface) (Foreign matter falling on resin)

Potential Problem / Defect : "Dry spots"
Nature of Defect : Area of reinforcement not wetted with resin (usually at laminate edge)
Possible Causes : (Not enough resin used, applies mostly to molding operations)

Potential Problem / Defect : "Pimple"
Nature of Defect : Small, sharp or conical pimple-like elevation on surface
Possible Causes : (Dripped resin or small bubble) (Worked on area after resin has started to cure)

Potential Problem / Defect : "Pit or Pinhole"   
Nature of Defect :  Small regular or irregular crater on surface, usually with nearly equal width and depth
Possible Causes : (Air bubbles that rise to surface which cure before smoothing out)

Potential Problem / Defect : "Resin pocket"
Nature of Defect :  Apparent accumulation of excess resin in a small, localized area
Possible Causes : (Improper lay-up in which glass separates and voids fill with resin)

Potential Problem / Defect : "Scratch"
Nature of Defect : Shallow mark, groove, furrow or channel
Possible Causes : (Improper handling or storage)

Potential Problem / Defect : "Wrinkle"
Nature of Defect : reinforcement
Possible Causes : (Improper lay-up) (Too rapid cure) (Use of old resin) (Fold in release film on the mold)