Things You'll Need
There are few things worse than having finished a large project using fiberglass, only to not have it fully cure. You let it sit, and sit, and sit, but it never completely hardens. Chances are you did not add enough catalyst, the chemical that hardens the resin. There are a few things that you can try to help the fiberglass finish curing. Sometimes these tricks will work, sometimes they won't. It's a chemical process and depends on how close you were to the proper amount of catalyst.
Set the fiberglass in the sun. The curing of fiberglass resin is an exothermic reaction, meaning that heat makes it work. Sitting in direct sunlight may give the resin the boost it needs.
Use a heat gun on the fiberglass. If the heat of the sun isn't enough, a more intense heat source may be needed. Be careful not to overheat the fiberglass, which can make it brittle. Keep a fire extinguisher nearby, just in case.
Spray a mist of catalyst onto the fiberglass with a spray bottle. This last-resort measure may be enough to kick off the rest of the fiberglass or it may only cure the surface layer.
Typically when fiberglassing it is better to use a bit too much catalyst and risk wasting a little material that to use too little and waste all of it.