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Offline Flyin6

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Plywood discussion
« on: September 09, 2019, 02:25:59 PM »
So I have been studying plywood grades and uses lately

There is a lot of good information out there

My particular interest at the moment is how to keep it weatherproof for an outdoor project

I thought I'd start with an exterior grade, dismissing Marine grade because of its cost. I estimate i will need 12-14 sheets in total.

The glue used in exterior grade is the same as used in Marine plywood, however the Marine stuff gets some African hardwood laminates on the inside, and more of them as well

Exterior gets 7 laminates in 3/4" size whereas Marine gets up to 11 layers

Cabinet grade is a good alternative having more layers and therefore strength than the grade C-D stuff we'd use as flooring, but to keep it moisture proof

I plan to coat it with polyester resin, then follow with a second layer of fiberglass mat then top with two coats of gelcoat. According to what I have read this is sufficient to create a water tank from any grade plywood

So what is everyone's experience with the stuff? And recommendations. My sizes will be 3/4" and 3/8"
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Offline JR

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Re: Plywood discussion
« Reply #1 on: September 09, 2019, 04:24:08 PM »
I used marine grade on the kids treehouse floor. Isn't it treated too? Held up well through the last rain but it still needs a coating.

For 11-2 sheets is the cost really that much more? Also he more layers, the better it resist warping and it stronger.
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Offline Flyin6

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Re: Plywood discussion
« Reply #2 on: September 09, 2019, 04:57:19 PM »
I used marine grade on the kids treehouse floor. Isn't it treated too? Held up well through the last rain but it still needs a coating.

For 11-2 sheets is the cost really that much more? Also he more layers, the better it resist warping and it stronger.
The cost is almost double per sheet, at least around here

Menards lists Marine grade at $59 a sheet, whereas CDX is in the $20's and PT 3/4" CDX is $32 a sheet. They also sell an interesting sheet which is 4 X 10 and grade B veneer, but that costs $63 a sheet and weighs nearly 100 lbs, so hard to manipulate.
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Offline Flyin6

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Re: Plywood discussion
« Reply #3 on: September 09, 2019, 04:59:04 PM »
There is a local sign company willing to give me all the furniture grade 3/4" I can take. It is the cut off remnants which average 4 X 4. It all has grade "A" veneers and I already have a supply stacking up.
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Offline Flyin6

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Re: Plywood discussion
« Reply #4 on: September 09, 2019, 04:59:51 PM »
Along with the plywood discussion, what is the best of the water proof wood glues?
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Offline Bigdave_185

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Re: Plywood discussion
« Reply #5 on: September 09, 2019, 06:53:52 PM »
What’s the purpose?


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Offline Flyin6

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Re: Plywood discussion
« Reply #6 on: September 12, 2019, 09:12:56 PM »
What’s the purpose?


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An upcoming project I am contemplating of something which will be exposed to the elements.
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Offline JR

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Re: Plywood discussion
« Reply #7 on: September 12, 2019, 09:20:24 PM »
How about the ZIP System ply that is made to seal homes? Not sure if it comes thicker?

https://www.huberwood.com/zipsystem/products/zip-system-wall
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Offline stlaser

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Re: Plywood discussion
« Reply #8 on: September 12, 2019, 10:49:21 PM »
What’s the purpose?


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An upcoming project I am contemplating of something which will be exposed to the elements.

Tac topper part two, suburban condo on the rise.....
Living in the remote north hoping Ken doesn’t bring H up here any time soon…..

Offline Flyin6

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Re: Plywood discussion
« Reply #9 on: September 19, 2019, 09:56:45 AM »
OK, getting ready to enter the plywood purchase phase

Was over at Menards looking at what they had

WHOA! Selection is off the hook. Much mo better-er than Slowes or HD.

So I was on to Baltic Birch plywood, 3/4" as the first choice, but 10 sheets at $69 per is some hefty weight. But with like 10 plies of all baltic birch and gude gluez, I's ah-likin it

Next up is a good selection of Marine grade 3/4" for $75 a sheet

Then there are various grades of interior cabinet grade stuff, birch, maple, and Oak veneers. The prices of that stuff is $53-$59 a sheet so I start to see a delta of $200 ish give-er-take.

Now I want to select the proper material, however, I do not want to overthink this because there is a cost component to all this that I will have to respect (Until my rich uncle dies in the poor house!). The whole project is likely to cost $6K-7K

So with the water proofing treatment and or sealing procedure I will use, I am not sure if it matters whether I use stainless boron steel or paper mache!

I'll use all waterproof glues. All edges will be treated with sealer and waterproofing paint like material. I'll prime it, then seal it on the exterior, then follow with two coats of raptor liner. The interior will get several coats of a spar varnish and seams will also be sealed with polyester resin.

So, given the water-proofing I plan to use, what I really need is a straight, structurally strong ply and nothing more.

Am I crazee? Well, let me be more specific, Am I crazee and over thinking the plywood selection?
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Offline JR

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Re: Plywood discussion
« Reply #10 on: September 19, 2019, 10:53:59 AM »
Since your sealing it, just get the most layer you can.

Here, HD has some 3/4 for $25 a sheet, good cabinet stuff. Must have been a special buy or something as that's cheap!
Retired LEO  Lifetime NRA+  Outcast in Calif

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