PT or Exterior Grade

[cbavier]

What is the difference between Pressure treat Plywood and exterior grade? I know one is wet and the other is in the Glue but for a Pontoon will the exterior grade be just as good for a deck? Will it last just as long?

 

[ezmobee]

Re: PT or Exterior Grade

I wouldn't want the modern PT anywhere near anything aluminum.

 

[mr 88]

Re: PT or Exterior Grade

If you are not going to use marine grade which has no voids in the layers then use the exterior and coat it with Polyester Resin and you should be good for 10 to 20 years. As EZ stated keep that PT away from the tin.

 

[oops!]

Re: PT or Exterior Grade

there is about 1000 threads on pt vs marine vs ext grade in the restoration section....

it will also tell you about why EZ doesnt want pt by his alum boat....

go to the restoration section and hit search

 

[cbavier]

Re: PT or Exterior Grade

If you are not going to use marine grade which has no voids in the layers then use the exterior and coat it with Polyester Resin and you should be good for 10 to 20 years. As EZ stated keep that PT away from the tin.

Does the Marine grade require it be coated it with Polyester Resin? Also what is the best way to join the sheets together?

 

[1fishbone]

Re: PT or Exterior Grade

Does the Marine grade require it be coated it with Polyester Resin? Also what is the best way to join the sheets together?

No
Tongue and groove.

 

[NYBo]

Re: PT or Exterior Grade

Exterior grade plywood will rot and warp. Sealing it against water is a must if you want it to last. Fiberglass mat or cloth with resin will do the job, and greatly strengthen it to boot.

 

[ezmobee]

Re: PT or Exterior Grade

Poly resin has no strength by itself. If you're wanting to coat it with resin to seal it, use epoxy. If you want to fiberglass it, you can use poly or epoxy. Marine ply is typically NOT treated against rot. It's just a higher quality ply with fewer voids and better glue.

 

[metriccrescentwrench]

Re: PT or Exterior Grade

Ditto what ez said. Marine plywood is much stronger than regular exterior grade, and a must for transoms. For a pontoon deck you're ok with exterior grade plywood, but it must be waterproofed with resin -again, as EZ aluded to, epoxy is better than polyester. Epoxy has about 5 times less water absorption than polyester, so IMHO is worth the little bit of extra expense.

 

[cbavier]

Re: PT or Exterior Grade

So it's really cheaper and better to just go with the Marine plywood. Thanks everyone for your response. I can get Marine plywood at one local lumber yard. I only need a 1/2 sheet 24"x 8ft. They probably won't sell a half sheet but it's worth a try and even if they don't I can keep the extra 1/2 sheet for some other outside project. What about joining the new 24 " to the existing plywood? Will a stringer be necessary do you think? I'm just extending the front deck to make boarding easier and make a larger fishing platform.

 

[metriccrescentwrench]

Re: PT or Exterior Grade

Marine plywood is NOT waterproof, it too needs to be either coated with resin or fiberglassed or it will rot. For what you're proposing exterior plywood is a cheaper alternative, with a proper coating to waterproof it.

I doubt if anyone can answer your structural questions without at least seeing some photos. I'm guessing you're talking about adding a piece of plywood approximately 4' x 4' in front of your existing deck??? IMHO that would need some support under it.

 

[Woodonglass]

Re: PT or Exterior Grade

I would HIGHLY recommend you look into MDO Plywood. It's constructed with MORE plys than Exterior Plywood it uses the EXACT same glue as Marine grade ply and uses a resin impregnated final ply that is highly water resistant. It's what most Hiway dept. use to make hiway signs out of if they don't use aluminum. Most Quality Lumber yards carry it. NOT Lowes or HD. It is More costly than Ext grade but less than Marine grade. IMHO the best way to go. Also you WILL need to construct some support for your extension.

Check out the MDO here...

http://www.pacificwoodlaminates.com/img/PDFs/PlywoodGuide.pdf



I'm just sayin...