Hello everyone! 
I recently posted a topic regarding a bridging issue we were experiencing with an infused carbon fiber part (http://www.talkcomposites.com/25379/Carbon-Fiber-Lifting-Off-Mould). Hanaldo gave some great advice and suggested that we work on positioning the bag more effectively before achieving a complete vacuum. So we worked on that and performed another infusion with 3 layers or 200gsm carbon and 2 layers of soric in between. We pulled the vacuum slowly, positioning the bag, and pressing the layers firmly into the corner of the mold. The end result was a substantial improvement. However, some bridging persists. Please refer to the photos attached below. Additionally, we also have a new issue: The soric is printing through the carbon quite a bit. I believe this might have been a curing issue as the temperature might have been too low. I should mention that we are allowing the vacuum to run for several hours after the part has been infused. This has not created an issue for us in previous parts but might be something for us to consider.

Any suggestions on how to completely eliminate the bridging issue and the soric print through are much appreciated.

***Photo of bagging during infusion:

***Photo of Bridging:

***Photo of Soric print through:

That is quite extreme print through.  Looks like you need lots more resin and still pay more attention to getting the material into those corners.  it should be possible to get that shape part to have a nice surface.   Also ensure you don't demould green - especially in this colder time of year as green demoulding can make print worse.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Yeh, as Warren said. That looks very lean, and still a bit bridged. Are you using a surface tack at all? It will reduce your surface finish quality, but it may help you position things a bit easier. Though honestly, that's such a simple shape you really shouldn't need it. How are you laying the carbon and the Soric into the mould? I would suggest making it a two person job, and get the next person to firmly press each layer into place as you lay it down, and then get the other person to place some pieces of tape on the edges to hold it loosely in position, more just so that you know you have enough material to allow it to drape into that corner (exactly as EC demonstrate in their "How to do a perfect resin infusion" video).

The resin is also an issue, it is dry and the degree of print through suggests it was very under-cured when you demoulded. Are you using an epoxy? It looks more like the results you might expect if you are using a vinyl ester or polyester, I've never seen this degree of print through with an epoxy before.

Did you clamp down both hoses, after you turn off the vacuum? As there is an area with almost no printthrough, it looks to me, as if air entered the bag in the green stage of the resin. This could also cause the bridging. Maybe your bag isn't leak free. I am not a fan of keeping the vacuum running. If there is a leak, the air would have to travel from the leak to the pump through the resin. So this only make sense with a perfectly sealed bag, and in this case, you could just clamp the hoses. In addition, I really advice against keep the pump running, if you do not degas the resin in a vacuum chamber. After closing the feed line, the overall pressure in the bag reaches the level your pump could achieve, wich should be low enough, to degas the resin in the bag, wich should be avoided at all costs.

Thanks a lot for all the feedback!

As Warren pointed out, it was rather cold when this part was curing and the resin was slightly tacky when we demoulded. This was very likely the reason for the print through as we have not had any issues with it before. Additionally, the resin going into the feed line ran out as soon as the resin had infused to the vacuum outlet.

We are using PVA as our release agent since that is what we have available. In our limited experience, a surface tack tends to lift the PVA off of the mould when the materials are placed in it, so we are not using one. We definitely plan on trying out easy-lease in future projects, but due to time constraints we are sticking to PVA for the time being. The method we are using to lay the carbon and Soric into the mould is probably one of the issues causing the bridging. For this trial, we used spray adhesive to stick the layers together on a flat surface. Then, we bent and pushed that stack into the mould. We are indeed using an epoxy, so I suppose the part was substantially under cured.

We only clamped the resin feed line and not the vacuum line. It is definitely possible that a leak caused air to get sucked into the mold and caused the bridging issue.

So, for the next attempt we will make sure to let the part cure for longer and to have more resin during the infusion. We will also lay the materials into the mould directly rather than sticking them together outside the mould and hoping it fits into the corners. We will use bits of tape at the edges to make sure we have enough material in the corners. We will also be more diligent in making sure our bag has no leaks and we will try clamping both lines.

I will make another post when we do the next trial.

Thanks again lads!

In my opinion, not clamping the vacuum line should have caused most of the problem. On the picture, I could identify a spot with far less print trough. By just demoulding to early, the print through should have been constant over the surface. However, if the part was still tacky, it was way to early for demoulding.

Yeh, I agree with both of oekmonts points.

Your issues with bridging are definitely stemming from how you are laying up, that is far too rigid a laminate stack to get enough movement with all the layers tacked together flat. You will find it much easier to simply place the layers in one by one, relatively loosely and just held roughly in place by a piece of tape. This would be more to prevent the layers falling off that vertical edge than anything else. Don't use any spray tack at all, in this case it is hindering you rather than helping you. Then you use the vacuum bag under partial vacuum to position everything fully.

You should have an idea now how much resin the part wants, but I would suggest working it out regardless. Just measure and multiply the length and width of your carbon to work out it's square meterage, then multiply that number by the weight in grams your fabric is, and finally divide that by 1.5 to get your resin ratio. So for example your carbon is a 200g measuring 500mm x 200mm then you do:

(0.5x0.2) x 200 = 20g
20g/1.5 = 13.33. 

So in that scenario, each layer of carbon would want 13.5g of carbon, so if you have 4 layers of carbon then they need 54g of resin. Do this for each different weight of fabric you are using, and then for the Soric it is simply 550g per square metre per mm thickness. So if you have 2 layers of 2mm thick Soric, each measuring 500 x 200, then you need 110g of resin for that, plus your resin for the carbon. And if you are using any flow mesh, this uses 700g per square metre. Then factor in 10% wastage on top of that.


This will generally give you more resin than you need due to the wastage factor, but not by much. So you can afford to make it a little more resin rich if you are wanting a perfect surface finish, or you can just clamp when the resin has totally wet out the laminate.

As Oekmont has said, you need a perfectly sealed bag, there's no.point leaving the vacuum on. The only time you can do this is if you are double bagging, and then you would clamp the resin outlet from the part but leave the outer bag under active vacuum. But it is better to just get a leak free bag.