Exterior Grade Plywood

I'm going to build a small stitch and glue canoe that calls for 1/4" plywood. I'm planning on using AC exterior grade plywood, and using glass cloth and epoxy on the entire exterior, and just epoxy on the interior. I'm to paint the exterior and varnish the interior after epoxy. Is it okay to use the clean "A" side of the sheet on the inside rather than outside? I want the clean wood because it will be varnished, but I wasn't sure if there are any differences between the A and C sides besides cosmetic. Thanks for any advice.

 

With the cost of ply in Maine right now, I would suggest looking at okoume marine ply, check out Boulter plywood in Ma. The quality of marine is so far superior to ext. it would probably be cost effective unless you only want the canoe to last for a couple of years, even then you'd have to recoat every couple of years.
I know that 1/2 and 5/8 available in Maine is 4 ply and is junk, and I'm talking about in residential construction, not boat building.

 

We have had some builders use exterior on smaller boat - none with very good results. One had a side panels crack in half (he then discovered there was a void running clear through the panel. Most of the problems are checking related, but thats not the main reason to stay away. If you can be sure there are no voids (or very little ones) than it will just be a finish issue.

Okoume is expensive for a dingy, there are other alternatives. Aquatech 6566 has very tiny voids (if any at all) and 1/4" is 5 even plys - it great wood for the price (much less than half that of Okoume 1088). It will also finish VERY nice

Joel

 

Chapman,
I built a stitch and glue canoe similar to what you describe, a "pirogue". I used glass cloth only on the seams. If I had it to do over again, I would use glass cloth over the whole thing, inside and out. It doesn't increase the cost or labor by much and you can still finish it bright on the inside. The advantage is that it will improve the integrity of the epoxy envelope around the wood. Without glass reinforcement, the resin could crack and allow moisture in. Especially if you're using an inexpensive (and thus lower quality) plywood.
Dave

 

check out the Meranti marine plywood at Maine Coast Lumber. It's not that expensive - espicially the 6mm/1/4 inch stuff - and will finnish better than exterior A/C

http://www.mainecoastlumber.com/marineply.html

 

Go for it,
yes keep best side inside, for varnishing. Make doubly sure you have no holes in planking when you paint as I have just found with black bitemen paint running down my varnished inside.
Ive made it out of exterior pine shuttering ply bottom(3/8) and exterior ply 1/4 sides will see how it stands up to UK weather!
Lets see what the pro's make of that!
I only which to sail on local canal so am not too worried!
Yours James