Polyester filler/autoclave issue

Hi there. I have a question concerning polyester fillers and autoclaves. At our raceteam we are modifying a fiberglass mould, in order to improve stability of the driver seat part which will come out from this mould.
Unfortunately, during the hand lay up on the mould, some voids of quite big dimensions were generated on it, so we have to fill them.
Since the final piece will be made with prepreg carbon fibers applied on this mould (and so, an autoclave will be used), is it a good idea to fill simply with a polyester filles, or is it better to use the same resin, which has been already used for lamination?

always best to use the same materials the mould was made from to do the repairs. Otherwise you will have CTE differences.

Ok, but there’s a problem since the clearances to fill are all in nearly vertical position, and the material used for the mould was glassfiber + vinilester resin. Can’t use glassfiber mat because the clearances are too small. I’ve already tried also to use only the resin, using adhesive tape to model it, but the resin comes out from it. Is there any material which can be put inside the resin, such as microfibers, microballs or maybe even something more hand-workable than microfibers?

yea, you can mix in milled fiberglass, or cabosil to name a few. You could also use just the gelcoat if the damage is not too deep. Hard to say without seeing the damage

Thanks for all!
Unfortunately the damages have been already filled and i have no image to show how deep the damage was, but i’m quite sure that only gelcoat wouldn’t have worked properly. I used microballs and the result was quite good, even if some resin have come out from the mold, because the holes were positioned in a quite vertical direction and there wasn’t a good position to avoid that.

Anyway, thanks for all!!!