Fillers are used to thicken epoxy for specific applications such as bonding or fairing. After selecting an appropriate filler for your job, use it to thicken the epoxy mixture to the desired consistency. The thickness of a mixture required for a particular job is controlled by the amount of filler added. There is no strict formula or measuring involved- use your eye to judge what consistency will work best. The diagram below gives you a general guide to the differences between neat (unthickened) epoxy and the three consistencies referred to.
Always add fillers in a two-step process:
Mix the desired quantity of resin and hardener thoroughly before adding fillers. Begin with a small batch-allow room for the filler.
Blend in small handfuls or scoops of the appropriate filler until the desired consistency is reached.
For maximum strength, add only enough filler to completely bridge gaps between surfaces without sagging or running out of the joint or gap. A small amount should squeeze out of the joints when clamped. For thick mixtures, don’t fill the mixing cup more than 1/3 full of epoxy before adding filler. When making fairing compounds, stir in as much 410 as you can blend in smoothly – for easy sanding, the thicker the better. Be sure all of the filler is thoroughly blended before the mixture is applied.
Spread the mixture into a thinner layer, either around the inside of the mixing cup or onto a flat non-porous surface or palette, to extend its working life.
Additives are used to give epoxy additional physical properties when used as a coating. Although additives are blended with mixed epoxy in the same two-step process as fillers, they are not designed to thicken the epoxy.
WEST SYSTEM pigments are available to color epoxy black, white or gray. Powdered pigments (tempera paint, colored tile grout, aniline dyes) and universal tinting pigment can be added to the epoxy mixture to tint it any color. Acrylic paste pigments (available from marine chandleries) can also be used to tint the mixture, as long as they are speci-fied for use with polyester or epoxy resin. 423 Graphite Powder will also color the epoxy black or impart darker shades to colors.
Generally, coloring agents can be added to the mixed epoxy up to 5% by volume with minimal effect on the cured epoxy’s strength. Always make test samples to check for desired color and opaqueness and for proper cure. None of these coloring additives provide UV resistance to the cured epoxy, so limit their use to areas not exposed to sunlight unless additional UV protection is applied.