Last week’s article looked at how resin and hardener are mixed and chemically react to form epoxy. The epoxy formed is useful, but can’t do all jobs. Typically unfilled epoxy is too thin to fill gaps or serve for fairing and filleting.

To enhance the epoxy there are a number of fillers. These include thixtropic fillers, bulking fillers, fiborous fillers and pigments.

Thixotropic substances are those that will flow when under stress. When not under stress, they do not flow. This makes them easy to spread, i.e. flowing under stress. When spread they then retain shape.

Bulking fillers are putty like and include microballoons.

Items such as chopped glass fibers and plastic mini fibers can be added to epoxy to increase strength.

Pigment fillers can be used to alter the epoxy’s hardness, tint the color, or as exterior coatings.

Michigan produced West System epoxy has a number of fillers which show how the general categories above are applied.

If you are using epoxy to laminate they make their 403 microfibers filler, which helps the epoxy, fill gaps.

If you are bonding hardware with epoxy the correct filler is the 404 High Density filler. This is well suited for bonding differing materials.

If your project calls for filleting, which is adding epoxy to concave or angled corners, use product 405 Filleting blend. This thickens the epoxy for use on the non level surfaces.

Filler 407 Low Density is best suited when you will be fairing or sanding the epoxy.

Other fillers include 406 Colloidal Silica, which can be used to stop epoxy from sagging and 410 Microlight which is smooth and good for applications where detailed sanding will occur.

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