If not marine grade, then what??? The mind boggling choices when it comes to plywood.

[delay18]

Ok guys, my mind is spinning with the options for my transom repair on my 1980 SS 160. Basically Marine plywood is not an option for me. No one carries it and they will only order it if I buy a whole skid. So I called a bunch of places in the area, and they told me that they use pressure treated. I expressed my concern with aluminum boats and they said that as long as it is coated and sealed it'll be fine and they have been using it for years. I wont be in any saltwater. I'm not sure if that makes a difference or not.

So I know this has been brought up, but I am hoping for some opinions/facts that are recent. So should I listen to the shops and use treated? If I seal it / paint is it safe? If not PT and Not marine grade then what? I walked into Lowe's and Home Depot (basically my local choices) and there is quite a bit of difference between them. Do I just get plain 3/4 pine ply? Should I step up to Oak or something better for strength? I don't see anything specifically listed as "exterior" grade that isn't pressure treated?

I'm sorry if this sounds stupid. This is my first real adventure in this type of boat and I am not a wood expert lol.

Links would be super helpful.

Thanks!

 

[g0nef1sshn]

I used acx from local lumber yard. Sealed in multiple coats of spar urethane. I wouldnt think of putting pt anything in mine after reading of the damage it does to aluminum. Sealed or not.

 

[jbcurt00]

There are LOTS of topics posted @ SCs on iboats. None use PT, of any kind.

Plywood is discussed in every one, and there are LOTS that are not just recent, they're currently being posted to.

 

[jbcurt00]

See my reply in your topic about the boat..
http://forums.iboats.com/forum/owne...rer/s/starcraft-boats/10122780-newbie-from-ny
This is a continuation of that discussion

 

[Watermann]

No way I would use PT ply and there are more reasons than it's corrosive effect on aluminum. PT has many knots and voids making it weak, it's heavy and it will warp badly as it dries out.

Just get a sheet of exterior grade 3/4" ply and cherry pick it for quality it will be fine.

 

[classiccat]

Are you anywhere near Newburgh, NY? If so, check out Heights Lumber.

 

[Grandad]

Just get a sheet of exterior grade 3/4" ply and cherry pick it for quality it will be fine.

Delay18, I agree with Watermann. I see little logic to use pressure treated plywood and then seal it so well to protect the aluminum that the plywood's integrity should never be at risk anyway. I'd use exterior grade plywood which has been laminated using waterproof glue to prevent de-lamination if it should ever get wet and which it won't anyway, if you're sealing it so well.

Yes, marine grade may be marginally stronger, but .....
My personal opinion, which may cause some controversy here, is that the voids in exterior grade plywood don't affect the structural integrity sufficiently to need marine grade without voids. You can get plywood rated "good both sides" that has no bad side, so any voids are all internal and bridged by the outside skin or get "good 1 side" and put the 2 bad sides together which also bridges any hollows with solid wood. Remember the opposition to bending a structure is based very much on the exterior skin, not its center (eg structural tubing has much more strength than the same volume of material in a solid bar). OK, rant over.
- Grandad

 

[Ike-110722]

Try MDO plywood. It's used primarily outdoors and in damp areas. Its used for signs and even daymarks on waterways. The glue is waterproof. Both exterior faces are resin treated.

 

[jbcurt00]

Try MDO plywood. It's used primarily outdoors and in damp areas. Its used for signs and even daymarks on waterways. The glue is waterproof. Both exterior faces are resin treated.

MDO good 2 faces/sides has both faces resin treated. The MDO I used was only good 1 face and about 40% cheaper then the good 2 faces.

 

[USMotorHead]

Why does StarCraft use Pressure Treated wood? At least that's what they advertise in there brochures.

EDIT:
Never mind, I think I may know why:

As noted previously, by several, NO PT! Anywhere on an aluminum boat. No, I dont care that shops you arent using recommended PT. Perhaps they are getting commercially available PT. Thats NOT what you can buy at HD or Lowes and as of yet, anyone thats priced it online discovered shipping to be nearly as much as the price per sheet, so double the cost of MarinePly. But that is an entirely different type of PT that isnt available to 90% of us.

 

[jbcurt00]

Some pontoons manufacturers do to. Its NOT the same as the PT available at the lumber yard, is kiln dried, and extremely hard to get. Shipping cost is almost the same as the plywood, so twice the cost of marine ply.

Being so hard to get retail, twice the cost of marine, and a different PT then what most find, its simply easier to say dont use PT

 

[Candutch]

Douglas fir acx or arauco acx I think are you best bets outside of marine ply. Arauco has limited knots and voids but I don't think it is as rot resistent as fir.

 

[Candutch]

Douglas fir acx or arauco acx I think are you best bets outside of marine ply. Arauco has limited knots and voids but I don't think it is as rot resistent as fir.

Cost wise that is, although I know nothing about MDO. It may cost less.

 

[North Beach]

Use whatever you decide but a couple items of clarification. Douglas Fir resists rot. And the adhesives used in exterior grade plywood are moisture resistant-not waterproof. Marine grade douglas fir plywood is made with waterproof adhesive. And voids DO weaken the structural integrity in plywood, I'm just not sure if there could be enough voids to do any harm in two half sheets of plywood. I guess you can tell I'm a big fan of marine grade plywood.

There are folks here who have used them all. They all feel that their approach was the best approach for their situation. None of them have seen the results of water and time in their builds, including me .At the end of the day, you need to use whatever you feel comfortable with.

 

[fishrdan]

Why does StarCraft use Pressure Treated wood? At least that's what they advertise in there brochures.

EDIT:
Never mind, I think I may know why:

Boat manufacturers use ACQ treated plywood which is not available to the public, it has an yellow/orange tint to it. The green CCA treated stuff available to the public is what everyone is talking about when they say not ti use treated wood in aluminum boats.

For plywood to use, I'd laminate up 1/2" 5-ply doug fir exterior, if it would yield the correct thickness. I would not use Arauco plywood as it will rot far quicker than douglas fir.

 

[USMotorHead]

Good info:

http://www.homedepot.com/c/discover_benefit_pressure_treated_wood_HT_BG_LC

 

[Watermann]

Boat manufacturers use ACQ treated plywood which is not available to the public, it has an yellow/orange tint to it. The green CCA treated stuff available to the public is what everyone is talking about when they say not ti use treated wood in aluminum boats.

For plywood to use, I'd laminate up 1/2" 5-ply doug fir exterior, if it would yield the correct thickness. I would not use Arauco plywood as it will rot far quicker than douglas fir.

2 layers of 3/4" is what I recommend and he'll only need 1 sheet of ply. If you have no option of using marine ply where you are then I stick with my advice in post #5.

 

[fishrdan]

2 layers of 3/4" is what I recommend and he'll only need 1 sheet of ply. If you have no option of using marine ply where you are then I stick with my advice in post #5.

That's fine, we all have recommendations, lots of different ways to do it. 1/2" 5-ply would be a better grade of plywood than normal 3/4" doug fir, closer in structure to marine plywood due to the thinner plys and more rigid. Probably the same cost as a sheet of 3/4 marine grade and have left-overs for something else.

Oh yeah, I had the treating mixed up, CCA = good stuff, green ACQ = bad stuff.

 

[Ike-110722]

I recommended MDO, but if I had my druthers I would use Marine even if I had to drive a long distance to get it. I recommended MDO because that is what the Coast Guard uses for their channel daymarks and signs on other aids to navigation. It is very durable stuff. I ran a USCG facility that serviced AtoN and made new signs for them. We used MDO and gave it a couple extra coats of paint as well before putting on the numbers and other decals. The stuff lasts a long time, in fact the decals wear out long before the wood does.

But if cost is the big factor exterior grade ply saturated with a thinned resin and then coated with two or three layers of resin will probably last the life of the boat. I have used it saturated with CPES (Clear Penetrating Epoxy Sealer) and then coated with resin. Five years later it's still solid even though it gets wet frequently. However, Warning! CPES is really toxic stuff and you need protective gear and a respirator to apply it. It is best left to professionals. You don't ever want to breath it or get it on your skin. It's really nasty stuff. But it will kill anything that gets in the wood.

You can do essentially the same thing with epoxy resin by thinning it so it soaks into the wood. It's not toxic but it doesn't kill bugs (or you for that matter) and you don't need a respirator and a space suit to use it.