Originally Posted by CCCLXXZ

The prepreg is partially cured which means that it is in B-Stage. It can be trimmed, pleated and formed using a knife or a pair of scissors. The prepreg handles very easily and because of its tackiness, it will lay tightly into your mold.* You might still have relief cuts or pleats to contend with just like you would with a dry fabric.*

After placing the layers in the mold, the prepreg must be compressed to allow bonding, to remove any trapped air between the layers and to squeeze out any excess resin. Although there will be very little excess, the resin will naturally become thinner as the temperature is raised and there will be resin flow prior to a full cure of the resin.* **

The needed compression can be accomplished using a press but unless the part is perfectly flat, a press is not an option.* Consequently, the part is generally vacuum bagged.* *

With prepreg fabric, there is a benefit in having plenty of time to build your bag and get the part ready for the oven.* You are not fighting the natural pot life of the resin.* However, the more layers you have laid, the more likely that there will be air trapped between the layers.* You should really have perfected your vacuum bagging technique before laying multiple layers of prepreg for a single curing.

A big advantage of prepregs is that after curing and cooling, additional layers can be laid onto the part without scuffing or additional surface preparation.* Again, up to ¼” can be laid at a single time with the same consideration of not trapping air between layers.

After the layup is complete, the vacuum bag is built and sealed, and you are ready to pull vacuum and begin the heat cycle.* There are 3 recommended cure cycles for Fibre Glast prepregs.* All 3 will produce similar properties.

There is an unconventional new prepreg out that can be stored at room temperature and can be layed up in stages. This is not consistent with traditional thermoset resin prepreg that requires handling and storage at sub temperatures.