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Composite Materials/infusion of carbon fiber FVF adjustment


I am attempting to fabricate a cosmetic near perfect carbon fiber part with that carbon under glass look. I am using hi quality Poly infusion resin in a reusable rubber vacuum bag tooling for a small part 30x30 inches. pulling a vacuum of 26 Hg (8.6 bar) at 4500' elevation (14,400m), I have no leakdown of vacuum. inlet tubing is 9mm, outlet to catch pot is 9mm, the path out from the reinforcement plies to my flow channel is restricted to one 2mmx25mm strip of flow media , complete wet out on release of clamp is 16oz at 18 minutes (in a 72f shop) through "greenflow75" to wet out 3 layers of 2x2 carbon twill. I have a 1 hour 20 minute working time to gel at 1.5% catilyst
My last problem that I cannot resolve is that I cannot acheive full wet out on the face against the mold. On demolding the surface appears dry , the fabric is exposed on the surface and is not glossy and smooth like the mold surface is, or a wet lay up result with the same mold. The backside has the appearance of full wet out. . The bag swells very slightly near the inlet about half way through the infusion and I have tried clamping off early, or letting the resin run into the pot but the results are the same after 12 attempts using different layers of flow fabric and fiberglass cloth in the sandwich, and just using 3 layers of carbon, then (very open pore)perforated release ply, the layer of greenflow75, then the bag.
The parts seem structurally excellent with low Fiber/Volume Fraction but the carbon fiber contacting the surface is not acceptable .
Is there a way to adjust increase the fabric wet out ?
or is it impossible to get a gloss surface against a mold with this system ?
gel coat is not an option because the fabric cannot be adjusted against tacky gelcoat and post finish topcoat defeats the goal

Hi David,

I'm surprised you're using polyester resin for the process - it typically does not bond well with carbon fibre and will be the weak link of the resultant laminant in terms of HDT, environmental resistance and compressive/tensile strengths.

However, there are a couple of ways to get a good surface finish against the mould, but would need detailed description and preferably photos of your set-up in order to help.

I'd be happy to consult with your company to come to a solution, feel free to contact me at email address below.



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andy mackay


Composite fabrication and testing, plug and mould design & build, surfacing materials, gelcoats, resins (epoxy, polyester, BMI, urethane) GRP, FRP, carbon, aircraft and marine composites, infusion techniques, Light RTM methodology, troubleshooting materials and process engineering.


11 yrs experience with aeronautical, marine and bathroomware composites.

Royal New Zealand Air Force Advanced Composites Course BCA Victoria University, Wellington, 1995

Past/Present Clients
Aeronautical, marine and bathroom ware composite cmanufacturing.

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