epoxy viscosity

how to increase viscosity

epoxy fillers

Epoxy fillers are incredibly handy, as they let you dial in the desired level of thickness — ketchup consistency, mayonnaise consistency, and peanut butter consistency.

• There are a wide variety of commercial epoxy fillers available to professionals. However, hobbyists often use at-home replacements, and any fine powder can work. Things I've heard suggested — baby powder / talc, flour, cornstarch, tapioca flour, the fine sawdust that's produced by an orbital sander, any solid that's dry and can be processed by a coffee grinder, and graphite.
• Products the professionals often use — fumed silica, microballoons / microspheres, and wood flour (which is sawdust that's been finely-ground).
• Ideally, porous surfaces should first be wetted with un-thickened epoxy, before adding the thickened epoxy on top.
• (Silicone can be thickened this way too).

wait some time

Epoxy gradually firms up as it cures, and there's a period where it's becoming somewhat stiff but can still be shaped some. Each epoxy product has a different quoted work time. If the epoxy is significantly colder or warmer than normal, that will definitely adjust the work time as well.

Some epoxies, such as Apoxie Sculpt, specifically advertise this feature. (On that page, they refer to "cure stages", such as waiting 10 minutes, or waiting 20 minutes. Total work time is quoted as 1-3 hours.)

cooling

If you cool the two components before mixing them, it will definitely thicken the epoxy [2]. However, air bubbles will stay trapped in the resin more easily.

how to decrease viscosity

additives

Adding lacquer thinner or denatured alcohol to epoxy will thin it out. [1] [2]

heating

Heating the two components before combining them also decreases the viscosity. However, I heard there's a limit, after which overheating decreases the working time significantly. (TODO — expand)