To sand or not to sand, that is the question….

I’m close to tabbing in stringers and bulkheads. The unfinished hull I purchased is a airex core with Kevlar / S-Glass hybrid fabric. In the interior, towards the bilge the fabric is well saturated with vinylester resin. However, as you move towards the shear (interior), there are sections where the face of the fabric is visible. Sanding in these places just creates a lot of Kevlar fuzz. I’m tabbing with epoxy and am under the assumption that all areas to be tabbed need to be well sanded. However, in these areas it seems I’m weakening the structure by sanding through this top layer of fabric. What do you guys think?

 

Gentle "manual" sanding/steel brushing/or steel pads http://www.govacuum.com/ladybug-steam-cleaner-stainless-steel-pads-6-pack.html maybe just to clean and scratch the surface

 

Unsaturated (dry) cloth represents the 'weak spot', NOT your sanding of same. There will never be a way to bond new resin to the resin that underlies the dry spots until the dry, unsaturated cloth is removed. Sanding on kevalr is just a PITA and there's no shortcut here. On small areas, you can use a twin or triple blade razor to remove the fuzz afterwards (this looks very silly but does work ) but I'm not sure if I'd give that a go for a large project such as yours. You should not leave the dry cloth, though; that's a manufacturing fault. Don't forget to add additional cloth and resin as needed to recover the strength lost by the omission of that last cloth layer, using sufficient overlap in all directions to the sound parts of the layup.

Jimbo

 

Thanks Jimbo, that's pretty much what I thought, including the additional layer to replace what has been sanded. However it is good to get confirmation from someone who knows this stuff. Fortunately, by the time I get all of the areas sanded for tabbing, it won't be that much more work to clean up the rest of it. You're right about the Kevlar being a PITA, but I think I'll skip the shaving as this is all interior and most of it will ultimately be hidden from view. I figure that if it leaves a bit of a bumpy surface I can live with it. Thanks for the input, these forums are really invaluable.

Best Regards,

Sea Jay

 

Ive found that sharp, new Zirconium abrasive discs (Like 3M Regalite or Norzon from Norton, Gator Grit at Home Depot) of medium grit (80-120) spun fast (10,000 rpm and up) on a right angle grinder cuts kevlar about as cleanly as you can cut it. Don't press hard, keep speeds up and change the disc as soon as it gets dull. Rougher grit works faster but leaves lots of fuzz.

Jimbo