Epoxy Additives

Epoxy is a fantastic two part glue with high strength but also high weight and costs. Epoxy is frequently used for bonding high stress areas as well as holding together items that a lot of other glues simply won't bond. Aside from the various epoxy types available off the shelf, there are other additives that one can add to the epoxy mix in order to alter its properties in a way that could be considered advantageous for a given situation.

Glass fibers / Chopped glass Adding chopped glass to mixed epoxy will enhance the strength of the epoxy and provide excellent gap filling properties. Be careful if attempting to sand down this mix as it will produce a lot of minute glass shards which can easially be a health hazzard or irritant.
Baby-powder / Talcum powder When mixed with epoxy, talcum powder will create a putty like substance that's quite easy to sand and is a lot less hazardous than the epoxy-glass mix though it will not have the same level of strength. This mix is slightly heavier than using microballoons however it's smoother and denser.
Microballoons Essentially the same as using talcum powder but results in a lighter mix that however will produce more pitting when sanded.
Thinning agents
Denatured Alcohol
Methalated spirits
Only add thinning agents to the epoxy after it has been mixed else it will potentially affect the completeness of the mixing process, resulting in epoxy that is permanantly sticky.
Thinning epoxy makes it easier to spread around and often provides a longer working and curing time.
As an example, if you mix 1 part epoxy, 1 part hardener and then once mixed add 1 part of denatured alcohol you will have a mix which is sufficiently thin to wick into carbonfiber tow or glass cloth but it's also sufficiently thick still that it won't run everywhere. It's recommended that you experiment with the epoxies available to you and mixing ratios, always keep a record of the mixes and your results.

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