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Discussion Starter · #1 ·
I'm ready to redeck my sled bed trailer and am looking at plywood. What are the thoughts about using the green ground contact plywood for trailer decking vs. regular pressure treated exterior plywood?

At the hardware store I saw the green ground contact plywood and it had something that looked like a white mold between each sheet. Is anyone familiar with this?

I called a lumber yard and their marine plywood is about $150 - $200 per sheet, needing 3 sheets, that's a little pricey for me.

Thanks in advance,

-AH
 

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Think you might be mixing terms up Andy. There are three distinct general varieties in your question - (Green) pressure treated, Outdoor rated (CDX) and marine. To make things more confusing each general variety has sub-varieties that overlap the other categories. The green pressure treated stuff is treated with a copper compound to resist rot and has waterproof glue. Outdoor just has outdoor glue, and marine has outdoor glue but is required to have less voids and meet some other standards. For instance here are the sub-categories of pressure treated plywood

UC1Interior Dry
UC2Interior Damp
UC3AExterior Above Ground, Coated with Rapid Water Runoff
UC3BExterior Above Ground, Uncoated or Poor Water Runoff
UC4AGround Contact, General Use
UC4BGround Contact, Heavy Duty
UC4CGround Contact, Extreme Duty
UC5AMarine Use, Northern Waters (Salt or Brackish Water)
UC5BMarine Use, Central Waters (Salt or Brackish Water)
UC5CMarine Use, Southern Waters (Salt or Brackish Water)
UCFAInterior Above Ground Fire Protection
UCFBExterior Above Ground Fire Protection
In any case, pressure treated used to be treated with copper arsenic which was toxic. The new compounds are much less toxic but I wouldn't use them in a boat situation or say for a garden box where the chemical can leech out. They make a great deck for a trailer though. Regular CDX plywood will work but will rot out especially if you keep a cover (fake turf) and keep it outside, Marine ply is overkill and will still rot if it's not pressure treated
 

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Discussion Starter · #3 ·
Think you might be mixing terms up Andy. There are three distinct general varieties in your question - (Green) pressure treated, Outdoor rated (CDX) and marine. .......... Regular CDX plywood will work but will rot out especially if you keep a cover (fake turf) and keep it outside, Marine ply is overkill and will still rot if it's not pressure treated
Great summary of the issue, Jeff! Have you ever seen the green stuff with what looks like a white mold on it? Either that's some kind of manufacturing residue or mold has evolved some bad-ass mutation that can live on that stuff!
 

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Forgot to mention that the new pressure treating chemicals are pretty corrosive to steel and aluminum. If you use pressure treated wood you need to put down a barrier between the plywood and any metal it sits on. (I used butyl tape) and it's a good idea to use stainless fasteners.
 

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I've seen the mold and yes I think it is actually mold but I suppose it could be some kind of chemical leeching out. Either way it goes away and doesn't come back after it dries out.
 

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Andy,

I recently replaced the boards on my trailer and I found sheets of 1/2" MDO from S2 Signs (Custom Sign Company - Denver, CO | Save 5% or More on Written Quotes) in Wheat Ridge. I recall them being $105/sheet (4' x 8'). I think they can order 3/4" sheets if needed. Allison was great to work with and they even cut 6" off the sheets for me since my trailer is 7.5' wide. So far so good with using MDO this time (decision based on past comments on Mountain Buzz). Just another plywood sheet for your consideration.
 

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Discussion Starter · #7 ·
Forgot to mention that the new pressure treating chemicals are pretty corrosive to steel and aluminum. If you use pressure treated wood you need to put down a barrier between the plywood and any metal it sits on. (I used butyl tape) and it's a good idea to use stainless fasteners.
Thanks, Jeff.

That's a significant issue and I think I may just use exterior grade plywood for the job.

-AH
 
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Check out Acre board. It’s expensive but forever.
 

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I'd second the suggestion for MDO.
It's what they make lotsa hwy signs out of, so you know it lasts. Has a nice smooth surface.

The deck of my raft trailer is ~18 years old, and is just now getting close to needing replacement.

My trailer is outdoors more than in.
 

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If you are looking at the plywood at a big box store you need to look at the back of the sheet. It should say it is made with exterior glue. They often get the stuff in the wrong bins and you think you are getting exterior grade glued plywood but it turns out not to be. Personally I haven't found any pressure treated or otherwise treated plywood that's worth a crap. It is ugly, splintery, and doesn't take a finish. I have been using 3/4" plywood with one smooth face and exterior glue specification, then you have to dado the outside edges down to 1/2" to fit under the side rails. you then have a entirely flat surface on the bottom to fit to the metal frame, and a good thick 3/4" plywood surface. Personnally I then coat it with 2 coats Flex Seal, or some polyurethane, or some stain and polyurethane. The only drawback to the Polyurethane or Spar varnish is that you in about a year you have to lightly sand it and put another coat on. 3 Sheets of plywood should be about $150 total and 1 gallon of Flex seal is about $90.
 

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MDO or similarly branded signboard works great. I painted mine inn3 layers of floor paint, trailer lives outside in Wyoming and is holding up great.
 

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Exterior grade plywood will not last any length of time unless heavily preserved and kept indoors. One season left outside and I would suspect it is delaminating already. I use plywood on a daily basis, the only thing I would use for a trailer is marine.
 

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I Just did this very thing with 4'x8' - 3/4" marine grade plywood from blodorne lumber in Wyoming for $82 a sheet. I also sealed the marine grade plywood with several coats of Behr water seal.
 

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MDO board sealed with an alkaloid enamel deck and patio paint. My trailer is going on 10 years of outside storage.
As other's mention, this is what highway signs are made of. For the $ and time invested you might as well have it last.
 

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Think you might be mixing terms up Andy. There are three distinct general varieties in your question - (Green) pressure treated, Outdoor rated (CDX) and marine. To make things more confusing each general variety has sub-varieties that overlap the other categories. The green pressure treated stuff is treated with a copper compound to resist rot and has waterproof glue. Outdoor just has outdoor glue, and marine has outdoor glue but is required to have less voids and meet some other standards. For instance here are the sub-categories of pressure treated plywood

UC1Interior Dry
UC2Interior Damp
UC3AExterior Above Ground, Coated with Rapid Water Runoff
UC3BExterior Above Ground, Uncoated or Poor Water Runoff
UC4AGround Contact, General Use
UC4BGround Contact, Heavy Duty
UC4CGround Contact, Extreme Duty
UC5AMarine Use, Northern Waters (Salt or Brackish Water)
UC5BMarine Use, Central Waters (Salt or Brackish Water)
UC5CMarine Use, Southern Waters (Salt or Brackish Water)
UCFAInterior Above Ground Fire Protection
UCFBExterior Above Ground Fire Protection
In any case, pressure treated used to be treated with copper arsenic which was toxic. The new compounds are much less toxic but I wouldn't use them in a boat situation or say for a garden box where the chemical can leech out. They make a great deck for a trailer though. Regular CDX plywood will work but will rot out especially if you keep a cover (fake turf) and keep it outside, Marine ply is overkill and will still rot if it's not pressure treated
Just make sure you use the proper fasteners to attach the deck, stainless steel or coated (for pressure treated) screws or bolts
 
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