Of the above, #1 is the most likely cause of big pin holes and #4 is probably the most likely cause of tiny pin holes.

Laminating Technique
Laying up a prepreg mould is very different to laying up a component. You really need to be making extensive use of cut lines, joins and smaller panels of material that can move around slightly, relative to each other. If this is done correctly, it should very unlikely that you'll get a large cavity or void.

Bagging Technique
Much the same as the components themselves, making a void-free mould with high quality edges and corners would need good bagging technique. Martin (Hanaldo) you'll have covered this on the course and this is basically what we're talking about here - really ensuring the bag is down tight into every corner.

Cure Cycle
In the case of the XT135 tooling system, this part should be REALLY straightforward which is why I've not listed it as a likely cause of your problems. The *initial* cure of XT135 is simply a slow, low cure at 65'C. After that cure you'll be removing it from the pattern and the bag before its post-cure. At this stage, you can see the surface finish.  Because there's no ramp or dwell or other complexity, I would be very surprised if the cure temp is the problem.

Material Condition
The XT135 surface ply is much more sensitive to out-life issues than the backing. The reason for this is the glass scrim which performs best when it is only partially impregnated with resin. At room temperature the resin becomes more liquid and will start to wet out the glass scrim (we call this 'wicking'). This means that the material works at its very best when it is at its most fresh (with the least accumulated time out of the freezer. Although from a resin perspective there is still plenty of 'life' left in the resin (even after 4 weeks +) the wicking effect, particularly in warmer environments, does mean that this is one system that will perform better the fresher it is.

I know - as suppliers of the system - that we're not exactly impartial in this but I can honestly say that in general we're getting a lot of positive feedback on this product and that it continues to surprise us with just what we can do with it. As an example, you may have seen some photos on our Facebook and Instagram of the carbon fibre frame that a local composites wizz/bike builder is making. We've supplied him with materials in exchange for documenting his project but we've not done the work or really provided any more input than we would with any customer. He's now made all of the moulds for the frame (there's more than 10 individual moulds needed) and they have incredibly complicated and difficult geometry and accuracy required. They've all been made using XPREG XT135 tooling prepreg and the surface finish is completely flawless on every mould.

Please both have a think about some of the above points and see if anything sheds any more light on possible causes for the problems. I would be very happy to thrash this out some more until we have you both making perfect moulds too!

All the best, Matt