Marine grade or Pressure Treated for floor replacement?

[Old Ironmaker]

A 3/4" 4X8 foot sheet of Marine grade plywood is going for $149.99 plus 13% tax up here. A 4X8 sheet of Pressure treated 3/4" Fir is $72.99 on sale this week. We will need 3 sheets. I say go with the PT for a new floor, buddy who is also rebuilding this boat with says Marine Grade. I would use a barrier of Ice and Snow Shield which is a water proof roofing material where ever the wood comes in contact with Aluminum. I have enough to do the entire bottom. My thinking is that an interior should stay as dry as possible, it will get wet if it rains or some wave splash happens on the water but you cover the boat when not in use with a good quality cover of Sunbrella or similar. My 94 StarCraft Superfisherman 190's floor is as solid as new, it never gets wet if I can help it.

I can't quantify how much more Marine grade will out perform PT. What is the advantage of Marine grade over PT and is Marine grade worth that price difference? Opinions please.

Thanks guys, Johnny D. (sitting here looking out at Lake Erie, a north breeze, pancake flat, rare, what a perfect time to take the boat out, soon, soon.)

 

[jbcurt00]

No PT in an aluminum boat. Everywhere the ply leaches the PT is at risk of corrosion, not just a point of contact.

Besides its wet and heavy.

If you dont want to pop for the 150 Marine. Get ACX fir plywood.

 

[ezmobee]

I would not use PT in an aluminum boat. I used regular exterior grade in mine sealed with epoxy. Marine grade is generally a superior product to exterior grade but not all marine grade is the same. "Marine" can mean more plys, cross laid plys, better glue, fewer voids, etc. You have to decide if it's worth it to you.

 

[jbcurt00]

Yep, if I could afford it, I'd only use BS 1088 certified Okoume marine grade, but its expensive....

 

[ondarvr]

"Marine grade" is a generic term, not a spec, but there are specs designated for wood designed for use in marine applications, just because it's a marine spec product doesn't mean it's rot resistant though. There are many different "marine" plywood's, most of the time in the US it means an OK grade of fir with a decent glue, but some product also comes from Asia. ​Pontoon boat shops sell treated ply that's better for aluminum, check the pricing on that stuff.

​Not sure what boat you have, but you may not need 3/4" unless that's what was there originally, more money, heavier, and no advantage if it's not required.

 

[82rude]

Short read that might help.http://www.joneakes.com/jons-fixit-database/2049-OVERVIEW-Living-with-Pressure-Treated-Wood

 

[roffey]

Old Ironmaker , sent you a PM. See if its what you are looking for

 

[Old Ironmaker]

Thanks all. Good info. I have sent you a reply roffey.

 

[roscoe]

http://www.araucoply.com/informacion2.asp?Submenu=1522&cat=1651&fin=1667&idioma=44

As close to "marine grade" as you can get, but at half the price. Sold in lots of big box centers like Menards, Homedepot, etc.

Have used it in 2 boats.
Sealed with SPAR varnish before installation.

 

[JASinIL2006]

That Arauco plywood is really good stuff, and way cheaper than marine plywood. I used it in my boat.

 

[fishrdan]

Arauco plywood is made from radiata pine, which is much more susceptible to rot than douglas fir....

 

[josh_booth]

I just asked my dealer the same thing last night. His answer was to buy regular plywood then treat it myself with a urethane.

 

[Old Ironmaker]

No PT in an aluminum boat. Everywhere the ply leaches the PT is at risk of corrosion, not just a point of contact.

Besides its wet and heavy.

If you dont want to pop for the 150 Marine. Get ACX fir plywood.

So if the plywood is sealed so it can't leach problem solved, yes, maybe, no? Did you mean to say Aluminum is at risk of corrosion?

We don't need 3/4 , it is overkill, we aren't tiling the floor. I truly believe in order to ensure there is not rotting of wood keep it dry. I don't think leaving a boat in a rain storm once will rot the plywood as long as you let it dry out well in the Sun.

 

[roscoe]

I just asked my dealer the same thing last night. His answer was to buy regular plywood then treat it myself with a urethane.

There are several ways to seal wood.
urethane would not be my choice.

You want something that will soak in and seal the pores. Spar varnish or epoxy resin such as West System are often used.

 

[jbcurt00]

No PT in an aluminum boat. Everywhere the ply leaches the PT, is at risk of corrosion, not just a point of contact.

missed a comma ^^^

Everywhere the chemicals used in the pressure treating process collects after leeching out of the plywood, the aluminum is at risk of corrosion.

Thats why holes are found in corners and seams as well as in the middle of a flat panel on the hull bottom. Not just where the PT plywoods is in contact w the aluminum.

If I wanted to use PT in an aluminum boat, I'd buy the kiln dried after treatment (KDAT) PT ply used by aluminum boat manufacturers, Starcraft included.

Finding that isnt easy, as no place anywhere near most of us is going to carry it. Same for the micropro stuff someone linked earlier and the BS 1088 ply I mentioned. If I have to pay to ship already expensive (by comparison to ACX Fir ply) 4X8 sheets of plywood, it becomes that much more expensive.

Even sealed, PT ply is heavy by comparison and is often still damp from the PT process. 2 huge negatives, IMO. I cant recall seeing readily available PT ply in anything but 3/4 either. So again shipping.

If you do seal PT in an attempt to prevent leeching, are 100% positive you'll leave absolutely no thin spots or voids in the sealing?

Every penetration into your sealed PT will need to be pre-drilled, including all the holes to mount the sheet onto the boats stringers if its the deck, plus seat pedestals etc. 100% of each hole will be 100% sealed?

Where are you drilling those thru holes into the sheet? While its lying in the boat or out of the boat on sawhorses? If its in the boat, all the wood shavings have to go somewhere when you thru drill. Are all those PT shavings sealed? And 100% removed from the boat?

Long way to lead me to the same statement:

No PT in an aluminum boat. IMO, not in a glasser either.

Besides, every buy a sheet of PT ply from your local lumber yard and not use it almost immediately? Most of that stuff tends to bend, twist or warp into a random potato chip shape if left to dry.....

So, again, buy marine or ACX Fir. Price MDO ply. That I can find locally in 1/2, 5/8 and 3/4 and is very nice ply, made for exterior exposure, and isnt as exlensive as marine, @40-70/sheet compared to about 100 for marine I cant often find and no one will order. 2 places will order MDO if they dont have it in stock. I only get good 1 side/face MDO. 2 good side/face is more $.

 

[pckeen]

Joining the chorus of voices saying absolutely don't use pressure treated. Anywhere it comes into contact with aluminum it'll corrode the aluminum. It'll corrode any fasteners you put into it (that's why deck screws are coated). Use regular exterior plywood if you are looking to save some money - it's inexpensive and will stand up well. Then coat the plywood with spar varnish or epoxy or paint to extend the life of the wood.

 

[fishrdan]

buy regular plywood then treat it myself with a urethane.

Yes treat it, but I wouldn't use urethane. Buddy of mine did that and it was cracked and flaking within a couple of years. WOG's recipe might work, sounds interesting, but I haven't tried it, boiled linseed oil, spar varnish and something or another. I would want the first coat or 2 very thin for max penetration.

There are 2 schools of thought on wood in boats, seal it so water doesn't get in (but if water does get in, it's trapped and will rot the wood), or leave it unsealed so it can dry out. I chose option 2 since I live in the desert and the wood will dry.

I used marine grade 3/4 ply in my boat as I didn't want spongy decks, then treated it with a borate solution: roach powder and laundry borax dissolved in boiling water. Something I dug up online - somewhere, a new process for treating wood. I wasn't 100% confident in the borate treatment, so I also treated the wood with Termin8. Cut all wood, drill all holes, then soaked in solution. I was doing this in the summer, in the desert, so it didn't take long for the plywood to dry after treatment, couple of days. I used the oil based Termin8, but if I did it again, I would use the water based -H20. The oil based Terminate stinks to high heaven, takes a long time to dry, and getting anything to stick to the residue, is, well, I wouldn't do it again.

FWIW, there is aluminum safe treated plywood, CCA treated, but it's very difficult to find, and expensive. It's what aluminum boat manufacturers use, IE: pontoon decking. "Easy to find" treated plywood is most likely the ACQ treated stuff that will eat your boat, DON'T use this as mentioned above. Green treated plywood is bad, yellow/orangish looking treated plywood is the good stuff.

I've had my rebuilt boat for 7 years or so and not a single sign of rot, but I'm lugging around an extra 200# due to using 3/4 plywood... If I did it again, I would toss around the idea of using either 1/2" douglas fir marine plywood or 1/2" 5-ply douglas fir to save on weight... I would still treat it with the borate solution followed up with Termin8-H2O, but that's me....

Also, just because it's "marine" plywood doesn't mean it's void free, the doug fir stuff I used was "virtually" void free. I hit a couple voids in my 3/4 marine plywood while screwing the decks down....

 

[Old Ironmaker]

Yes treat it, but I wouldn't use urethane. Buddy of mine did that and it was cracked and flaking within a couple of years. WOG's recipe might work, sounds interesting, but I haven't tried it, boiled linseed oil, spar varnish and something or another. I would want the first coat or 2 very thin for max penetration.

There are 2 schools of thought on wood in boats, seal it so water doesn't get in (but if water does get in, it's trapped and will rot the wood), or leave it unsealed so it can dry out. I chose option 2 since I live in the desert and the wood will dry.

I used marine grade 3/4 ply in my boat as I didn't want spongy decks, then treated it with a borate solution: roach powder and laundry borax dissolved in boiling water. Something I dug up online - somewhere, a new process for treating wood. I wasn't 100% confident in the borate treatment, so I also treated the wood with Termin8. Cut all wood, drill all holes, then soaked in solution. I was doing this in the summer, in the desert, so it didn't take long for the plywood to dry after treatment, couple of days. I used the oil based Termin8, but if I did it again, I would use the water based -H20. The oil based Terminate stinks to high heaven, takes a long time to dry, and getting anything to stick to the residue, is, well, I wouldn't do it again.

FWIW, there is aluminum safe treated plywood, CCA treated, but it's very difficult to find, and expensive. It's what aluminum boat manufacturers use, IE: pontoon decking. "Easy to find" treated plywood is most likely the ACQ treated stuff that will eat your boat, DON'T use this as mentioned above. Green treated plywood is bad, yellow/orangish looking treated plywood is the good stuff.

I've had my rebuilt boat for 7 years or so and not a single sign of rot, but I'm lugging around an extra 200# due to using 3/4 plywood... If I did it again, I would toss around the idea of using either 1/2" douglas fir marine plywood or 1/2" 5-ply douglas fir to save on weight... I would still treat it with the borate solution followed up with Termin8-H2O, but that's me....

Also, just because it's "marine" plywood doesn't mean it's void free, the doug fir stuff I used was "virtually" void free. I hit a couple voids in my 3/4 marine plywood while screwing the decks down....

Thank you Dan, great reply. The choice we are going with in the future is exterior grade Fir (Canadian made) covered in Spar Varnish and wrapped in Snow and Ice where fastened to Al. Snow and Ice basically melts into the screw and wood sealing it.

 

[daveydoodle]

Affirmative no PT, I just replaced a floor that had pieces of PT---you could see the corrosion after 2 seasons in Mi. Not only the contact but any standing water in bildge will rot the metal. Not to mention the inherent warping .

 

[daveydoodle]

I can attest to PT wood on aluminum- I fixed up an old alum. open bow that the previous owner tried to fix up too in bow seating area. In addition to all the warping , the alum. in bow keel low areas was not much thicker than alum. foil. Found when drilling out some leaky rivets. Stay away from PT. wood.