That 3 ply (5 ply) stuff from Home Depot ... I used it on a pirouge I built last year. I just got through sanding all the paint and primer off. Above the water line, but below the rail I found a few places where I apparently had not gotten sufficant saturation. It started to decay and weaken. After digging that out and filling it back with; 1st thin epoxy ( till almost cured ), then thickened epoxy ( like a paste ), sanded smoth, and hand rubbed a coat of epoxy all the way around like a thin film. Just finnished with the oil base primer, and 2 coats or oil base enamle, think I am going to put on one more coat before I apply a wax coat to that. There was no problem in any of the cloth ( 6oz. ) covered areas or any place that was covered sufficantly by epoxy. The inside was fine and it only has tape at the chines but it is all coated verrrrry well, and stained, and UV protected. My others I have made from this ply were clothed completely on the outside, ( bottom and sides, including under the gunnals)
They were painted inside and out and have have no problem with checking or delamination.
I don't like the how flimsy it is on the bottom between the frames.
( I expect to get blasted by someone for this one ) but when I cut my bottom frame I build in a 3/16 crown to frame #2 and 1/8 in #1 and #3. That realy gives it life.
And I still call it a flat bottom. Come on 3/16 over 2 feet. Thats not enough to call it any thing else.
Let me add I only do this for mine and with the luan on my pirogues. I would never sugest that you change your plans, or any kits to incorporate the use of cheap ply.
My Glouchester Dory recomends nothing less than 1/4 inch exterior ply and that is what I am using and I will not be altering from Mr. Bogler's design.
Same will go for the Selway Waterman and Pete, when I get to them.