Hi!

When molding carbon parts with high Vf (>50%) the fibres touching the mold are leaving a residue on my mold surface. I don't know why this is happening. I just bought easy lease release agent, but it also happened with wax (Partall). In fact I thought the Partall wax had aged so I bought Easy Lease thanks to this forum. But unfortunately no difference. The parts are demolding easy though with easy lease.

I have been using different curing processes: 24h room temp, 48h room temp, 24h 30 degrees C, 48h 30 degrees C. All with the same outcome: a residue on the mold. The molds are machined of PU toolingboard (Renshape) and polished to a mirror surface. Epoxies used are L + GL2 / S / L and EPH161 from R&G. When making a hand layup of one ply of carbon without compaction there is no printthrough and also no residue on the mold surface after demolding just like when using a gelcoat prior to the lay up.  So it looks like the problem is related to the compaction of the fibre or it maybe an epoxy problem.

My initial thoughts are it might well be a problem with the surface of the board in combination with the additional compression under vacuum.  This is assuming your cure cycles are fine for the resin system you have (not being familiar with your resin I cant be 100% sure but the times look realistic for curing for most epoxies). Most modeling boards are to an extent porous dependent on density. The higher the density, the more solid they are. It could be you are on the borderline with that PU board such that you get away fine under hand lay but the vacuum pressure is just enough to cause issues. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant