Epoxy is unlike anything you are familiar with, so to understand it you must compare it to things you may be familiar with.

Epoxy is similar to pancake syrup. At room temperature it is fairly thick. In colder temperatures it will become thicker and in warmer temperatures it will be thinner. Don't put epoxy on your pancakes!

So external temperature is an important variable in viscosity when handling epoxy.

The wild card is the hardener. To change the epoxy into a solid, a hardener is added to create a chemical reaction and this chemical reaction produces heat. This internal heat generated by the epoxy mixture is greater when the epoxy is in a mass like a mixing cup, or it can be slowed by spreading it thinly in a flat tray (like a roller tray) or spread in a thin coating. So warmer epoxy cures faster, cooler epoxy cures slower.

So to work with epoxy you must think about the external heat, room temperature, and how the hardener creating internal epoxy heat will work with or against the external temperatures. Typically, if you have colder temperatures you would want to use a faster hardener to counter the exterior cold with interior epoxy heat. BUT, since the cold external temperature will make the epoxy thick and the fast hardener will cure quickly this scenario is a poor one for wetting out fiberglass cloth as the thick resin will cure before the glass can be saturated.

If you are working in higher room temperatures you would add a slower hardener to counter the room temperature influence to make the epoxy cure too fast.

AND warm room temperatures will make the epoxy thin and slow hardeners will give the epoxy a long cure time, both of which are ideal for wetting out the fine twisted fibers of glass in fiberglass cloth to a transparent condition.

So the pancake syrup poured on a surface will self level over time, since the viscosity is not changing.

The moment you mix in hardener, the epoxy is getting thicker, reducing it's leveling capacity.

Epoxy, while it may initially appear similar to the pancake syrup has a hardener which is changing the viscosity from the second it is mixed in, so the epoxy may or may not have enough time to level as it cures. Most often the epoxy does not have enough time to level, so it reflects the rough texture of the fiberglass cloth.

Faster hardeners and warmer temperatures also make the epoxy molecules dance faster so they will cure (freeze) in a rougher surface.

Each epoxy manufacturer has different ideas of what an epoxy should do, so they mix different additives giving each epoxy different characteristics.

I have worked with West System epoxies, MAS and System Three epoxies. Each is different and the hardener combinations of each epoxy add more variables.

If epoxy is applied to the smooth surface it can create a smooth surface when cured.

So I apply fill coats, glass seams and stems and rough sand the whole boat to a smooth surface. Then I apply two new coats of epoxy which are nearly as smooth as the finished varnish.

Rob