Hello,
I need some help making a decision on what plywood to use on the deck of my weekender. I should say off the top that although I acknowledge that Marine Ply is probably the best choice, it's just not in my budget. (maybe for the next boat)
I found a great deal on 1/2" fir core, occume "skinned" exterior grade plywood for the bottom. Nice to work with and I haven't noticed any voids yet. Mind you the stuff they sent me was actually 3/4". I figured that was probably not a bad thing for the bottom and used it anyway.
So now I need 3 sheets of 3/8" plywood and my choices are:
A) Use the same plywood as I did on the bottom. They don't carry it in 3/8" so I would have to use 1/2". $34.99 (cdn)
B) They have what they call factory fir. Which seems to be good one side fir plywood. $27.99 (cdn)
C) Home Depot has Spruce sheeting for $12.99 (cdn)
D) For comparison's sake I can get fir marine ply for $58.99 (cdn)
I am concerned about the fir checking in the areas that won't be covered in fibreglass cloth. I will be coating it all in epoxy but understand that checking can still be a problem.
Please help. I have really enjoyed reading everything on this forum for quite a while now. I only recently (finally) registered.
Thanks in advance,
Steven Goodman
Welcome to the BYYB Steven!
While I'm no expert on wood selection... I would reccomend that you use the marine grade. Since, as you say, you only need 3 more sheets and it would cost only $72 Canadian total more than the other ply that you have already purchased, I think you'll be a lot happier 5 years from from now if you use the marine grade. The extra $72 is a drop in the bucket compared with your total build budget. That's my $.02 anyway...
Welcome aboard!!!
- Steve
Steven:
I've been having good luck with "select grade" plywood. It's standard rotary cut spruce/fir plywood with the surface veneers on one side filled with putty. Since the boat is going to be painted anyway - I didn't care about that. There are some internal voids but I'm willing to take the chance as the boat will be spending most of its time on the trailer covered up. The "select grade" was a fair price savings over "good 1 side" which is basically what the Stevensons recommend and a substantial price savings over marine grade. I do see that the prices are there on the "left coast" are a lot lower than here in Ontario marine grade - but then you've got all that cheap softwood lumber that the US doesn't want to buy ;-)
WITH THAT SAID - I do agree with Steven that marine grade will last longer and you will have less trouble with it. The surface veneer is also a big issue. Most fir plywood is rotary cut and will "check" or crack over time. Coating it with fiberglass is the "best" solution to that. The Okume may well resist that.
I hope that helps.
Hello Steven,
If it is 3/8" ply then there a lot of things to consider. But the primary consideration is the number of plys and the quality of the glue in addition to the primary face grade.
For example, 3/8" for general construction use has only 3 plys, with a thick center ply of more or less unknown quality or species. And voids. Generally not rated for exposure to elements. The outer plys are thin and unless graded A or B will not be good choices for painting.
Most all Marine quality plywoods have 5 plys, with three even thickness center plys and two face plys that were the same thickness before they were surface sanded. All marine plys have waterproof glues. Almost all of them have no voids and any voids are generally quite small and not really significant. If the surface plys are A and C as an example, use the C ply with plugs in it for the surface to be coated with glass, use the better grade ply for the paint.
Most domestic plywood is rotary cut from peeler logs so the grain will be wild. Nothing really wrong with that at all, but if you sand it you take away the softer grain and leave the harder annular growth rings. Result is uneven surface. So avoid sanding it if at all possible. Just knock of any surface defects, fill others and prime with a high build alkyd (oil based) primer. Then sand and if needed fill on the primer to make fair. Then prime again and sand, etc. until you end up with a surface that is essentially the way you want it to be. Then paint it with a good exterior grade latex paint in thin coats. Two coats should last a long time and won't show checking on the interior surfaces to any great extent. This would be the best grade of ply side to paint. Then glass the lesser quality side and finish the same way. The resin will fill the small spots with plugs in it and the glass will help to prevent any checking from occuring.
Occasionally, if you call some sign making companies and ask them where they get their MDO plywood for signs, they will refer you to their source. You will be able to get 5 ply 3/8" DF or Spruce Plywood with a resin impregnated paper surface on both sides ready to finish or glass. Either one. Not as expensive as the imported materials but then if you are painting and glassing it is going to give you what you want and then some. Little more expensive than the common grades but less than marine. Worth looking for.
They make highway signs out of this stuff with 24/7/365 exposure to the elements and paint both sides and edges of this stuff, it holds up extremely well. It is also easier to use.
The issue with using thicker grades of plywood than called for in some areas is that you end up with unequal forces/stresses coming into play in the structure. Out of the design criteria and it occasionally is weaker on most boats than what is called for. And you will probably find that with some searching around you can find what you need, but probably not at the nearest places to get it.
I, too, would recommend the marine ply, especially if you have already used it this far. If, however, you do need to use ACX or select plywood, Rule #1 is patience. There are really good sheets of ACX plywood out there. But you have to find them yourself. Look at all the edges. Reject any sheets that have even one gap between plys. There will be some gaps you can't see, so keep them the a minimum by rejecting the obvious ones. There will be 5 - 10 sheets like this in a unit of lumber, even at Home Depot, and boat builders are the only ones I know that are looking for them.
Good luck, and post some pictures of your progress.
Thanks for the insight and the extra push to keep looking for a better option. It turns out there is an independent plywood retailer right near where I work. I got there contact info from a local sign company. (good advice)
Now I can add 3/8" MDO at $22.00 per sheet to the list of choices.
Also, they sell something called Riverside Underlay that is made with fir plys and waterproof glue. The salesman told me many boat builders were substituting it for marine ply due to cost. It runs $28.50 per sheet. I'm going to take a look today.
Thanks for the help,
Steven Goodman