Light cloth vs 3 coats epoxy

[54bullwinkle]

Getting ready to start my ECO 18 build 

For non structural waterproofing can one epoxy coat with 4 oz cloth substitute for 3 coats of epoxy?
Thinking of using it on non structural applications ( under deck, frames, under gunnels, ) for waterproofing in addition to 10 oz cloth where needed.  

[Captain Tim]

Three thin coats of epoxy might be less epoxy than what you would need to wet out the cloth.

Three coats of epoxy would have a better chance of full coverage with no voids

[54bullwinkle]

Gotcha.  Thanks

[Alan Stewart]

I wouldn't bother if it's going to get 10oz over it later but I am a fan of putting down 4oz on something if i need to finish it quickly but you still usually need a "fill coat" on top of the glass if you want it smooth. If you put too much epoxy then the glass just floats and you still get the weave. I find the best is to do a heavy coat on the bare wood and put the 4oz glass down and let it soak up the epoxy and let that set up then a few hours later come back and coat that again as a fill coat. OR use peel ply over the 4oz then it's a 1 step and done. It is heavier than 3 coats though. If the parts are flat on the table though you can just do a heavy flood coat but it's hard to know how much there is and easy to use a LOT. Sand the ply smooth with 220 before you coat if you want to try to do a one step flood coat for best finish else you could still get some wood grain/fuzz rough texture on it. 

 

 

[54bullwinkle]

Thanks Alan

[Andy B]

Forgive the possible stupidity, but can someone explain some of these areas need epoxy?  I'm thinking under the gunwales, seats, even the deck.  It seems to me they get wet so little that primer and paint, or varnish, would be enough.  What is the deciding criteria for whether epoxy is needed or not?

[Alan Stewart]

Epoxy always needed on everything everywhere. That's the best method. The epoxy is a barrier to moisture. Moisture makes wood shrink and swell. Shrinking and swelling causes cracks. Cracks let in more moisture. Full epoxy encapsulation of all wood is the best most long lived way. Okoume plywood is not very rot resistant at all. If it's wet it will rot in a couple seasons. The Gougeon Brothers built the adagio Trimaran in 1969 and she's still going strong. All epoxy and plywood bonded and i'm sure every bit is coated in epoxy. 

[WindyBeard]

I would think plywood with even a light cloth on both sides would be a lot stiffer and stronger than plywood with only epoxy.  Would this let one go to a thinner plywood and save overall weight?

[Alan Stewart]

save weight maybe but at the cost of stiffness. Thickness = stiffness. 6mm ply is stiffer than 4mm ply with a layer of 4oz on either side and probably lighter too. 

[WindyBeard]

Makes sense, ok.  My experience is coming from my cedar strip kayak (my last build and only design) where no strength or stiffness came from the core material, really.   

[Dnjost]

I am into year 11 with my CS 17.  It lives outside on a mooring all summer, and under a snow tarp in the winter.  Water will eventually stand in the bilge if left unattended for a while.  I did have a little rot in the ply (starboard side of floor, bottom near center, just aft of the CB trunk) where the bilge water sat and the paint system failed.  Hindsight being 20/20, I would definitely apply a layer of 4 oz on any surface that may have standing water on it.  Do the Floor up 6" from the bilge on cockpit sides.  even the deck and seats could benefit from a light layer of cloth to keep the paint system intact. I hate painting.  

 

The repair took no more than a couple of hours over a couple of days and I am fortunate I got it early on.  Good as new now and raising hell off southern Cape Cod. 

 

On a side note,  I added a Yamaha 4hp with an external gas tank, and loving my expanded range.  Now, just need time to sail!  

Edited August 15 by Dnjost
missing information

[Jason Klett]

This thread got me thinking, would the 4oz help with overall durability? I am now considering using it in exposed cockpit areas that just call for epoxy coating for my Marissa build as well since I will be using the boat for fishing and know that can beat up finishes like paint and gelcoat (hooks, sinkers, fish spines, etc...). I know it will add a little weight but I think the tradeoff would be beneficial if it means less likelihood of penetrating that waterproof seal during use. If it won't make much of a difference I'll stick with just epoxy where it's not calling for fiberglass. 

[Alan Stewart]

Definitely makes good sense on high exposure areas like exposed outside corners, cockpit coaming edges, console edges. I did some of that on my sailboat like the corners of the seat tops. 

[Steve W]

Skeena is 7 years from launch and is holding up very well. I coated the entire top, including the comings with 4 oz cloth. It's super easy to work with and I would definately do it again. And of course it strengthens the joints.

 

I also added glass to the seat tops. Impacts from the sprits and general banging of my paddleboard paddle, dropped coffee cups, and other dumb stuff has confirmed the decision. I don't think it addds much weight. 

 

I backed into a mailbox by accident while the boat was on the trailer, which would have surely broke into the plywood of an un-glassed cabin. The glass helped spread the impact and while it got a good scuff and needs a touch up, away I went on my trip last fall when it happened.