Marine plywood raft floor- ?'s - Mountain Buzz
 

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Old 6 Days Ago   #1
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FtC / Rancho del Rio, Colorado
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Marine plywood raft floor- ?'s

So I'm gonna try to use a sheet of 3/4 marine grade plywood for a floor board on my 16foot Hyside. With the cooler, water jugs, kitchen box and rocket boxes on it, I figured it'd be stronger than those plastic sheets....
But. Should I coat it with something??
My last floor was just cheapo plywood, and it only lasted a couple trips.
Is Marine plywood good enough on its own, or will it rot and de laminate too??
Should I coat it in urethane??
I assume things like Thompsons Water Sealent for decks would be bad for the rubber...
Maybe just linseed oil??

What do you guys think?? Anyone else using a Marine plywood floor??

Thanks for any input I can get!!

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Old 6 Days Ago   #2
 
Frisco, Colorado
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I painted mine with a couple of coats of deck/porch/patio paint from Lowe's, has held up great for a couple of seasons now.
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Old 6 Days Ago   #3
 
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Hampden, Massachusetts
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I have a plywood casting deck that I applied a few coats of polyurethane. Had no problems when I stored the deck in the garage. But when stored outside for two months, the polyurethane cracked, splintered and began peeling off (UV and rain damage). Your mileage may vary.

I like your linseed oil idea.
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Old 6 Days Ago   #4
 
Defiance, CO, Colorado
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Skip the marine plywood, cover with spar varnish or marine paint, probably need to re-coat every year or two
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Old 6 Days Ago   #5
 
Loveland, Colorado
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I painted mine with the epoxy one uses for bar tops. Made sure to get the edges good. I threw some light sand on it for traction. It's been in use for a couple year and seems and looks brand new to me.

https://www.homedepot.com/p/FAMOWOOD...0080/301826159
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Old 6 Days Ago   #6
 
Wondervu, CO, Colorado
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I have built several plywood floors and can share my experience...

1. Plywood comes in lots of grades. Marine grade is great, but you could get by with an exterior rated XCD or XAC
(X = exterior glue A,B,C,D = is the grade of surface finish, A grade is knot free, B grade has knots cut out and filled with 'footballs' D grade will have exposed knots and voids in the layers) 3/4" thick is good, I tried some at 5/8" and was too bouncy. Don't use pressure treated plywood, the treated wood won't help and the splinters are toxic.

Here in Colorado the marine grade is not commonly stocked. You will probably need to special order it. Not all marine grade is rated for exterior use.

2. Exterior deck/patio paint will out perform spar varnish or polyurethane varnish for all wet contact applications. Linseed oil will not work well underwater.

3. Seal the edges and voids before painting. The exposed grain at the edges, knots, and voids will suck water deep into the plywood. Seal these with 2 ton epoxy thinned with denatured alcohol (thin to the consistency of cream) I like to give one coat to all exposed edges, then a second coat over the whole board.
2 part wood filler or auto body filler is good for filling voids.

Note: epoxy alone has poor UV resistance. This can be corrected by over painting with deck/patio paint. Or by adding UV blocking pigment to the epoxy.

I have some deck boards made of 3/4" XAC plywood that are still going strong after 5 years.
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Old 5 Days Ago   #7
 
thornton, Colorado
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This!!!

Quote:
Originally Posted by kengore View Post
I have built several plywood floors and can share my experience...

1. Plywood comes in lots of grades. Marine grade is great, but you could get by with an exterior rated XCD or XAC
(X = exterior glue A,B,C,D = is the grade of surface finish, A grade is knot free, B grade has knots cut out and filled with 'footballs' D grade will have exposed knots and voids in the layers) 3/4" thick is good, I tried some at 5/8" and was too bouncy. Don't use pressure treated plywood, the treated wood won't help and the splinters are toxic.

Here in Colorado the marine grade is not commonly stocked. You will probably need to special order it. Not all marine grade is rated for exterior use.

2. Exterior deck/patio paint will out perform spar varnish or polyurethane varnish for all wet contact applications. Linseed oil will not work well underwater.

3. Seal the edges and voids before painting. The exposed grain at the edges, knots, and voids will suck water deep into the plywood. Seal these with 2 ton epoxy thinned with denatured alcohol (thin to the consistency of cream) I like to give one coat to all exposed edges, then a second coat over the whole board.
2 part wood filler or auto body filler is good for filling voids.

Note: epoxy alone has poor UV resistance. This can be corrected by over painting with deck/patio paint. Or by adding UV blocking pigment to the epoxy.

I have some deck boards made of 3/4" XAC plywood that are still going strong after 5 years.
Pretty much how I do it. I have had floors last 12+ years. Light sanding and retouching with deck paint every year, where needed.
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Old 5 Days Ago   #8
 
Salida, Colorado
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Quote:
Originally Posted by raymo View Post
Pretty much how I do it. I have had floors last 12+ years. Light sanding and retouching with deck paint every year, where needed.

Use this stuff, https://www.penofin.com/wood-stains/...n-stain-sealer


It's the bomb, recoat once every 5 years or so.. Marine plywood is overkill..
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Old 5 Days Ago   #9
 
NE, Oregon
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Just use MDO and skip all the sealing and maintaince..
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Old 5 Days Ago   #10
 
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Kalispell, Montana
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Quote:
Originally Posted by Willie 1.5 View Post
Just use MDO and skip all the sealing and maintaince..
Lots of people swear by MDO. I haven't, but have heard enough to do so next time.


I'd still want to seal the edges.
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