This is my first time working with fiberglass. I'm working on a small fender for my race car. Ultimately, I'd like to do these and some other parts in carbon, but it seemed wise to spend some time practicing and learning with cheaper materials.
I made a mold of an existing fender using tooling gelcoat, fiberglass cloth and polyester resin. That worked really well, and I'm happy with the mold.
But, my first part did not turn out so well. In most places where there are relatively sharp bends, I'm getting large (1"-2" long) voids, which I assume are due to air bubbles forming where the 225g fiberglass cloth separates from the mold while curing.

Any suggestions on how to address this? Should I be using CSM instead of cloth? I've seen mention of others using spray adhesive to keep the glass in place, but I'm not sure how that might affect the mold release. (I'm using spray PVA.)

Original part (which was cleaned up after this shot, before working on the mold):


Top outside edge. The voids are clearly visible.



Leading edge with some clay and stuff still hanging on.

Some good advice above, but if you'd like to continue trying to improve results with your current wet-lay process using polyester resins, then applying a coat of clear polyester gel coat ahead of laminating your reinforcement will help

If you can get the timing right, then the tack of the gel coat just before getting to a more hardened state can help hold your fabric into the corners better. However, this doesn't really allow much scope for re-positioning things so you'll need to be quite good at laying the fabric in cleanly if a neat weave alignment is important. 

You might still suffer with some air entrapment, but hopefully not at the scale you've already seen and the gel coat surface on the finished part might allow for some repairs if any resultant bubbles can be pierce and filled

However, on parts with quite sharp corners and other detail, using vacuum is the best route forward in terms of achieving good cosmetic results, not least because it will help to force the fabric into the detailed areas and ensure you get a better fabric to resin ratio. Again, as stated above, if you do decide to invest in a pump, you could then move on to working with carbon and epoxy, with an excellent prospect of making very good looking parts after a bit of practice