Is one type of plywood better than another?

[gunner1]

I'm ready to replace my transom and my question is this- I was in HD and saw they had not only maple plywood but also oak plywood along with the regular plywood. Would there be enough of an advantage to using the oak or maple to offset the $25 to $30 price difference?

[cheesegrits]

Use marine plywood. The hardwood ply at HD is not exterior grade, it does not use waterproof glue. The problem with the exterior ply at HD is it is full of voids or air pockets. If you try to bolt something through it, sure as anything you are going to hit one of these. Try to find okume marine ply it is the best! The best grade of ply gets a rating of BS1088 which is kind of like ISO9001.

[109jb]

As cheesegrits mentioned, the hardwood plywood is not exterior grade. I do however disagree that you need to use marine grade. Many boat manufacturers used regular old exterior grade plywood. My Sea Ray is a good example. The boat rotted out from severe abuse. When I pulled it apart I found CDX plywood was used almost exclusively in the structure of the boat. That includes the transom, stringers and deck. I say CDX because they all had non-filled knot holes. During my rebuild I am using a combination of CDX and ABX plywood.

I see that you are rebuilding a Starcraft. Being an aluminum boat you will want to stay away from pressure treated lumber as is can cause corrosion of the aluminum. I had a 16' Starcraft Supersport that I replaced the deck in and I think I used 5/8" CDX on that one and sealed the wood with spar varnish and then carpeted. It worked just fine for the remaining 9 years I owned it. If I were to do an aluminum boat today I would still not use marine grade, but I would probably still use 1/2" CDX and coat the wood with fiberglass on top and bottom. If coated with fiberglass top and bottom, the CDX will outperform bare marine grade in every way (strength, water resistance, durability) and still be cheaper.

[ondarvr]

As with most things in life, there is always something better if you want to spend more money. If you start researching marine ply you'll find many different products designed for different applications and for $30.00 more there will always be a better option. Its all up to you on how much you want to spend, but if you do spend more, go the marine ply route, not the HD product.

[j_martin]

Marine plywood is supposed to be free of internal voids, however the last that I bought (at a big price) did have voids. Any more I buy will be ACx from a lumber yard.

Any plywood needs to be sealed real well. I use a clear penetrating epoxy sealer, several applications. Any holes in it have to be sealed as well, with a marine sealant like 3M 4200, or 5200. Silicone doesn't last, or seal well enough.

hope it helps
John

[Floyd M]

Plywood rating system as I understand it is:

Marine grade (no voids and waterproof glue)

Exterior Grade (small, filled voids, waterproof glue)

Exposure I (larger filled voids, some small voids not filled, waterproof glue often of lesser quality than above)

Exposure II, III Voids, regular glue,.....issues

Most wood in HD or Lowes is Exposure I at best. Often the signs will say exterior, but that does not mean exterior grade, it means for exterior application. An example of this is ACX. Hope this helps.

Keith

[JaSla74]

Standard 3/4 inch BC exterior grade should do you fine. I would also suggest staying away from big box stores & get your plywood at a lumber yard.

[Numlaar]

Myself, I don't care for any of the plywoods at either HD or Lowes.. as mentioned the quality on them is mediocre at best...

Also, most home stores the plywood is 3 or 4 plys depending on the rating...

For my rebuild project i went a slightly different route...

I worked at a cabinet shop, and there they get shipped in from specialty vendors, stuff called "Verola"... its an 8-10 ply 3/4" cabinet grade plywood...

Because it's soo many plys, this stuff is indestructable, you can't bend it to save your life!

Now, being cabinet grade its "supposed" to use waterproof glue (kitchen/bath applications), so it seems to hold up really well.

As long as you seal whatever wood you choose, I think you will be fine...

I used this in my transom (two pieces laminated together with fiberglass then glassed over), and its way stronger than the original 2 pieces of CDX crap they used when the boat was built.

the other nice thing is, the way its made, there are no voids, and the surfaces are exceptionally smooth (its designed to simply be stained and its good to go, no sanding needed).

Cost on it 2 years ago was about 35 bucks a sheet and is far less expensive than marine grade, and far superior quality IMO.

You can check with a local cabinet shop and see if they will sell you some.

Hope that helps!

[Mr.Swee]

I agree with several post here. You can use marine grade that is always the best. AC Fir is exterior plywood that comes water, chemical resistant and is already dry and straight. If your boat is being left at the lake all the time, then go with marine grade. If the boat sees the water during the weekend and then goes home and gets covered, use AC fir.

Do not use the pressure treated plywood from a lumber store. That will warp once it dries possibly breaking the fiberglass and causing more problems. I hope this helps. Just my opinion.