Builders' Forum Archives
Posted by LeeG on Jan 26, 2007
3. if you want numbers you can find it but it'll take searching. Graphite makes the epoxy softer and slippery. If you want slippery it's just the thing. If you store the kayak upside down in hot southern sun it'll get hot enough to fry an egg.
If you want DURABILITY as in resistance to scraping impacts as opposed to ease in dragging over rough surfaces you need a more durable laminate. Which is primarily a function of thickness of the epoxied skin and it's constituent fabrics.
If you drag a graphite painted bottom over your roof rack or over a beach it'll slide VERY easily. If you come onto a beach IN your kayak and bump up against submerged rocks it'll slide past the rocks a bit more easily but if the impact is not glancing then the energy is dumped on the hull bottom whether it's covered in epoxy, paint or an aluminum canoe.
You can make test panels and judge for your self by scraping it with a sharp rock. My $.02 is that if you added another layer of 4oz glass you'd get more resistance to scraping impacts than a few mil thickness of slippery epoxy.
Another way to think of it is painting a sheet of 4mil plastic with graphite epoxy, paint another with plain epoxy, layup 4oz glass and epoxy on another sheet. Now test those three samples for resistance to scraping impacts. It's obvious that you'll break right through the thin coats of epoxy and the epoxied cloth will actually resist intrusion. That's what you're trying to prevent on the bottom of the hull, scrapes and impacts that can break the watersealing epoxy and expose the wood.
Ok, but you don't want to "add weight". The only way you can increase durability without increasing thickness and weight is to use a different material with higher abrasion resistance that doesn't soak up more resin. Which pretty much points to s-glass for the bottom or using a light fine weave glass instead of the two coats of graphite.
My $.02 is that if you wanted maximum durability for the least amount of money and excess weight put on a "football" section of 3.25oz 'tightweave' glass from RAKA. It's almost the same amount of glass as 4oz e-glass but with finer weave. You could probably put down one layer of this glass with one fill coat for nearly the same weight as a thick coat of graphite and actually have a layer of something that will resist the kind of damage that breaks wood before it scrapes along it.
In Response to: Graphite by Julian on Jan 23, 2007
- Re: Graphite by LeeG on Jan 26, 2007