Fiberglassing Overview

Fibreglass as we know it was invented by Russell Games Slaytor of Owens-Corning. It is made by extruding silica or other glass compounds into small diameter fibres. At 1700+ deg F., the silica softens and is able to be moved. It is cooled rapidly, not allowing the glass to form an ordered structure.

The fibres are bundled together and spooled. The bundles are then woven, chopped or milled.

        Benefits of Fibreglass:

  • Does not expand or shrink with temperature change.
  • Does not absorb water.
  • High strength to weight ratio.
  • Non-flammable.
  • Chemical resistant (except for hydrofluoric, hot phosphoric acids, and strong alkaline substances.)
  • Electrical insulator

Fibreglass Cloth

Fibreglass cloth is a woven fabric. Plain weave, satin or twill are of the weave styles we carry. Click here to learn about fibreglass weaves. The 5.6, 6, 7.5 and 10 ounce plain weave fabrics are the most commonly used. In this most simple weave pattern, warp and fill yarns are interlaced over and under each other in alternating fashion. The Plain weave is the easiest to handle since it does not unravel as much as the other weaves when cut.

The satin and twill weaves are slightly stronger and more pliable than the plain weave and are easier to conform to curved surface. They are more difficult to handle than the plain weave.

We carry a four-harness and eight-harness satin weave. In the four-harness satin weave pattern there is a three by one interfacing where a filling yarn floats over three warp yarns and under one. The eight harness satin is similar to the four harness satin except that one filling yarn floats over seven warp yarns and under one.

The twill weave is more drapeable than the plain weave and maintains more fabric stability than a four or eight harness satin weave. This weave pattern is characterized by a diagonal rib created by one warp yarn floating over at least two filling yarns.

Chopped Strand Mat

Chopped strand mat (also known as fibreglass mat) has short strands of fibres held together with a resin binder. The fibres are randomly oriented. Mat is only compatible with polyester and vinyl ester resin. When resin is added to the mat, the binder dissolves and the fibres can be moved around. It is easier to conform mat to tight curves and corners than it is with weaved fabric.

Chopped strand mat is the least expensive fibreglass and is often used in mold construction or projects where thickness is needed. Mat is, also, often used as the first layer (before the gelcoat) in a laminate to prevent print through. Print through is when the fabric weave pattern shows through the resin.

Chopped Strand mat does not have much strength. If you need strength you should choose a woven cloth or you could mix the two. Mat can be used between layers of woven fabric to help build thickness quickly and aid in all layers bonding well together.

Woven Roving

Woven roving is a heavy material used when thick laminates are needed. Fibres are bundled and yarns are oriented into two directions. It is commonly used in boat and large mold construction. Woven roving does not drape easily but is strong.

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