I need some help, I just recieved my first order of prepreg and after playing with it for the last couple days I am horribly disappointed.  I have been working with other prepregs from another supplier and I have had pretty good success with conventional prepreg that is meant to be cured in an autoclave even though I have been using it in an out of autoclave process.  So far the first 5 things I have tried to make with easy preg have all been complete failures.  I am super frustrated because I spent a lot of money to buy a couple yards of the material and have it sent to the US and at this point I am feeling like it all needs to be thrown in the trashcan because it seems completely useless.  I will describe the setup that I am using and maybe someone can tell me what I might be doing wrong.  I will also attach some pictures of the problems I am having.  I have tried metal molds, composite molds with a gelcoat surface, cnc machined solid teflon molds, and tonight even a sheet of glass to see if I could get a good surface finish and so far all have failed miserably.  For my mold release I am using a chemical release called Freekote 700nc which has performed beautifully with the other prepregs I have used.  I am vacuum bagging with a flexible bagging material called stretchlon 200 and with a solid release film and a breather cloth.  I have used cure schedules all over the map from 180 deg F for ten hours up to 275 deg F for less than an hour and all have yielded similar results  The max amount of vac I am able to achieve here is about 26.5inches of mercury and that has proven to be acceptable for the other prepreg I have used but I am wondering if it is not enough for the easy preg because I have read a couple of places that a near perfect vac level above 29 inches is necessary.  I leave the vac pump running throughout the process every time.  To top it all off I am not at all happy with how the cured fiber looks and  find it to be some of the most boring carbon fiber I have ever seen anywhere.  There seems to be such a lack of contrast of the alternating fibers that it almost doesn't even look like carbon fiber at all, I would hope that if I could get my surface finish issues resolved the appearance might also improve but I am skeptical that it will ever look as good as any of the other various  fabrics I have worked with.  For me the selling point of this prepreg was that it was great for making cosmetic parts and I am disappointed to say the least.  I appreciate any input that I can get and really hope that I am doing something wrong and that I can learn to love this easy preg!  Thanks for your help.

Hi Trev,

I use a surfacing system from Umeco (VTF261). It seems identical to the easypreg surface (single sided, 200g 2x2 twill), so the result should be the same as yours. VTF is VERY aesthetic. The resin has a slight dark grey tint to it which deepens the carbon effect. At £45 a metre though, I treat it as if I was laying down gold tissue. Heres the first layer:



I reinforce it with some low temperature 600g carbon. Here it is straight out of the mould:



I think the problem is your temperature. I dwell at 65C for 3 hours then ramp to 90C for 3 hours. I have found it to be a good balance of resin flow and time. 180F is about 80C. At that temperature, the resin is gelling before it has time to settle. Also, it will have cured in about 6 hours, so you wasted 4 hours of oven time there. You need to let the resin flow at a much lower temperature before you crank it up.

Also, I wouldn't even think about putting my part in the oven unless I have a perfectly sealed bag and a full vacuum. Are you doing a drop test? Furthermore, running the vacuum while it cooks doesn't compensate for a leak, as small as it is. The vacuum is working on the leak instead of applying pressure. Although I keep the vacuum on while it cooks, even with a perfect bag. When the resin starts to flow, any possible trapped air wouldn't be sucked out otherwise.

Are you living at a high altitude? Maybe around 1.5 kilometres above sea level? Just wondering because you say "The max amount of vac I am able to achieve here"  Depending on how critical things are, you could get an absolute vacuum gauge. Its a gauge that measures vacuum against an internal vacuum chamber as opposed to the ambient air pressure.

P.S. Fahrenheit?  Inches of mercury?  Yards? This doesn't help the process at all!

Thanks so much for your reply.  The results you achieve with your fender are exactly what i am after and give me hope that I can improve my processes to achieve the same results.  The barometric pressure is right at 28 in of mercury most days ans with any of the three vac pumps i have tried I am able to get a max of 26.5 in of mercury so not a perfect vac at all andthat could well be my problem...I hope so.  I would go buy a new vac pump if i knew it would fix the problem for sure i just dont want a third pump sitting around for no reason.  I will also try the ramping method of heating that you mentioned this weekend as what you are saying makes sense.  Since the fabric did not come with any time/temp data sheets i simply based my first cure off of the 100 deg C for 10 hrs that is noted in the easy composites tutorial for working with their prepreg.  I also start with a preheated oven just like it says in their tutorial and perhaps the resin is gelling before it has a chance to flow into any small pinhole voids resulting in the finish i am getting.  I will dedicate some time workingnon it this weekend and report back with the results and i am really hoping it is simply operator error!  I would like nothing better than to have this stuff do exactly what i need it to do.  Thanks again.  Sorry to about all of the imperial units of measure but herenis a metric one for you.  My house is at an elevation of almost exactly 400 m

At 400 metres, your maximum vac will be around -0.94 bar.
Test both your vacuum and your gauge by plugging the gauge straight into the vacuum hose. If youre not pulling -0.94, either your gauge is out or your pump isn't pulling. I have a gauge kicking around that will say -0.87 when in reality its a full vacuum.

If your pumps aren't pulling, I would also try throwing 2 connectors in the bag and run dual pumps, or hook both pumps up to a manifold then go to the bag. See if you get closer then.

As for your bag, you need to work in an almost clinical environment when making it. A single carbon hair falls on the tape and your bag is ruined. Most leaks are in the tape. Make sure the bag is stretched when you tape it and once its all enveloped, grab the edge of the bag with the tape and stretch it. The tape will stretch further than the bag, filling voids.

Once you do all that, do a drop test, if the needle moves the slightest in the first 30 seconds, its no good.

Here's another piece I've done, same materials. This one has had a coat of satin:

Beautifull fender.  PerhapsI have not been as careful as i need to be when bagging.  I will try a setup this weekend where i bag in a very carefull manner and then curenusing the ramp up that you have suggested.  I will let you know how it turns out, and thanks again for all of your input.

I'm sure you'll get there. Another helper is debulking. Once you've tested the bag and befoere you bake it, hook it back to the pump and leave it running. After some time youll hear creaks and sounds coming from the bag where a bridge gives in to pressure. I sometimes debulk for up to 24 hours depending on the size and complexity of the part. In fact a part is back at the shop debulking as I write this post! Debulking won't work unless your bag is perfect though, as the pump will just be working on the leak.

I went and purchased a new vac pump and gauge today (pic one)  and refined my bagging methods some and saw significantly better results but I still have a ways to go.  The barometric pressure here today was 28.5 in hg (725 torr/mm hg).  I worked and worked on joints until I could achieve 27.5 in hg 698 torr/mmhg neat my bag.  That is also the best I could achieve with the gauge connected directly to the pump so I could be that the gauge is not quite reading correctly, or that my new pump won't quite get to a near perfect vacuum.  I will attach a second picture that shows the improvement from the first plate that I showed in my original post.  I could not really get the voida to photograph well so I filled them with a paste polishing compound which dries white so that they can be seen clearly.  The plate on the left that looks worse is the original and the plate on the right is my new improved plate.  Tomorrow if I get a chance I will try a ramped cure as suggested with a hold at an intermediate temperature for a couple of hours to allow the resin to flow more completely before it gels to see If I can improve even further on todays results.  I am attaching a third picture that shows todays plate with a skull I created previously.  This picture shows the difference in appearance of the carbon I was using previously with easy preg.  The stuff I used before looked SOOO much better.  It is hard to capture it in a photograph but easy preg is downright boring looking compared to the stuff that the skull is made of.  There is a much lower of contrast between the alternating layers that I wish I could find a way to improve but I think it must be related to the weave of the actual fibers.  I find it a bit ironic that the non cosmetic aerospace stuff that I was using before can look so much better that "cosmetic" grad carbon cloth.  I am determined to make this stuff work, or burn thru all of it trying!

Again, I can't talk about easypreg, only the Umeco product I use. When you say "cosmetic" do you mean clarity?

You are right me saying it looks better is just a matter of opinion but I want my carbon fiber to really look  like carbon fiber with lots of definition and contrast along with the look of depth that the 2k clear coat gives it.   To me the easy preg looks very muted and it seems to lack the extreme contrast that in my opinion makes carbon look so great when well done.   I am using a pretty normal looking polyester breather over a solid non perforated release film with stretchlon 200 as s a bagging material.   Today or tomorrow as time allows I am going to experiment with a ramped cure like you suggested to see if I can eliminate even more of the pinholes.