I seem to be getting an occasional problem with brittle resin. I am not sure whether its a problem with the resin cure or with air entrapment. The excess resin in the mold is very brittle and weak, and some of the part extending to the flanges of the mold is delaminates, with a sugar frosted appearance

Its a hand laid vacuum bagged part, carbon and diolen mix, epoxy EL2 resin, with a mix of fast and slow hardner.

With all my parts I am using the lowest vacuum possible generally around 90%, and at least 85%.

Usually its fine but ive had a couple of crap parts.

I  have used  a heat gun on a low temperature to soften the CF reinforcement when placing, so I am wondering whether thats interfering with cure. It does give a bit of vapor off from the resin. However one of the times it went wrong i hadnt done this.

I am wondering whether its there is too much dry fabric and air is escaping while the part its curing and mixing with the resin, or just too much air escaping during curing.

I have been exprimenting  with using less peel ply to control the resin-fibre ratio better. So i use peel ply around the edges of the mold near the flanges but none over the centre of the part, and i weigh the resin out to aim for a certain resin-fibre ratio. In the centre of the part i just use impervious film. The compaction seems much better than normal (less wrinkles), and excess resin collects near the flanges instead of in the centre of the part. The resulting part is much closer to the target weight.

ill try just slow hardner on the next attempt but any ideas welcome.