I have a carbon fiber race canoe that was originally constructed using vinyl ester. The hull is being patched using epoxy and carbon and then refinished with and epoxy/ graphite mixture.  I have seen information the mentions a wash/ surface prep is required prior to using the epoxy.  I haven't been able to locate any information on what is required for the prep.  THank you in advance for any and all assistance.

Gary

Give the surface a good key with 120 grit paper and a thorough clean and it should be fine.  To be fair most resin surfaces keyed heavily and cleaned should enable epoxy resin to get a good grip. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thank you Warren - the initial CF/ epoxy patch that was placed peeled fairly easily as well as the refinishing seemed to peel after getting it back on the water.  As far as cleaning, is there a specific type of solvent to use for this?  Generally it's just an acetone wipe down. 

The mechanical key is almost more important than the cleaning. It needs to be well keyed. 

Generally what I do is wipe the part thoroughly with soap and water to remove any water borne contamination, then thoroughly rinse to get rid of any soap residue (alternatively just wipe down the panel with a damp cloth and then there's no need to rinse).

Then dry the panel, and clean again with a solvent to get rid of any wax/grease/chemical contamination. Acetone isn't ideal for this because it is too volatile and flashes off very quickly, which just redeposits the contamination on the surface again. Its better than nothing, but I prefer to use a slower flashing solvent like MEK (protect yourself from exposure to this) or even a panel and paint solvent like wax and grease remover. Wipe on with one cloth liberaly soaked in the solvent, then before the solvent flashes off wipe it off again with another clean, dry cloth.

Then do your abrasive key with 80 or 120 grit paper (the rougher the better,  but you dont want to damage the panel further by abrading too harshly). Then ideally just remove the dust by blowing off with compressed air, and you're good to go. If you haven't got compressed air you can do your solvent wipe again, but this actually makes it more likely that you introduce contamination to the freshly exposed virgin material. 

Very much appreciated - we were just talking about switching to MEK.  We have performed many epoxy based repairs on three other boats but hadn't dealt with a vinylester base previously.  Thanks again!

Vinyl ester is easier to bond to than epoxy, it has quite an active surface energy. But really I treat all panels the same, whether I'm bonding to polyester/vinyl ester/epoxy/phenolic/plastic, etc. Same prep-work, then an appropriate adhesive/resin. Plastics can be difficult, but everything else works provided the prep is right and the adhesive/resin is appropriate.