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Adding Fillers and Additives

Fillers

Throughout this and other WEST SYSTEM manuals, we refer to epoxy or resin/hardener mixture, meaning mixed resin and hardener without fillers added; and thickened mixture or thickened epoxy, meaning mixed resin and hardener with fillers added. 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 particlular 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:

1. Mix the desired quantity of resin and hardener thoroughly before adding fillers. Begin with a small batch-allow room for the filler.

2.  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

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.

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