With infusion the key to perfect parts is a combination of things. The critical one being a perfectly sealed bag. I know how hard and frustrating this can be. Even the smallest of leaks will have a negative effect on the surface finish. When your starting/learning don't start the infusion without a perfect seal no matter how tempting it is to "give it a go" you will almost certainly be disappointed with the outcome and waste expensive materials.
With experience you can make a judgement call. If the leak is tiny you are unlikely to find it until you introduce the resin, this is still risky but does work. Start the infusion, as soon as the resin reaches the area of the leak you will see air being draw in indicating the leak point. Most small leaks are caused my a punctured bag so start applying small pieces of gum tape to seal the hole. You have to work quickly and as said is risky.
The other main issue is bridging, ie where the stack is not against the mould surface, tight corners, recesses etc. These will leave voids that will either fill with resin or leave dry areas. either can ruin the finished part.

Good luck and let us know how you get on.

Warren

Carbon Copies Ltd

The bag leaking air will be my next problem watch lol

Thank u warren I'm going to give it all a go 2day any other tips b4 I start 

Not quite. The gelcoat is only on the surface giving a thicker surface layer. Using the other method the whole stack is resin rich. Also the GC50 provides UV protection, much better than clear coating the part afterwards in my opinion.
Also when using heavier weight cloths for the surface layer even a resin rich part with have a slightly uneven surface. With the gelcoat you can get a glass flat finish.

Warren

Carbon Copies Ltd

Although using the gelcoat would technically make it resin rich as well, it's essentially doing the same thing. 

If I am going for a perfect cosmetic finish I actually do the opposite. Once the resin reaches the vac outlet and all the stack is saturated I clamp off the vac line but leave the resin line open, the length of time depends on the size of the part but anywhere between 30-60 seconds for most of the parts I do before clamping off. This gives a resin rich (slightly heavier) but pin hole free finish. If weight is more important I do the opposite.
If you use GC50 gelcoat you can get a perfect finish without having to make the part resin rich.
Hope that makes sense.

Warren

Carbon Copies Ltd

So do u clamp off the resin feed and still leave the vacume pulling for abit to degass it in the bag?

Yep.

Carbon Copies Ltd

Even with the easy composites resin ?

Don't normally bother de-gassing either (unless I have had a particularly good curry) careful mixing is usually enough.

Warren

Carbon Copies Ltd